computer network - yll.edu.hk · web viewthere are several data type in programs. they include:...

ICT Chp 21,22,23,24 Problem-solving procedures and Algorithm

Problem-solving concepts

1. What is problem-solving?

Problem-solving is a process of analyzing the description of problem until we reach a solution. To

solve complex problems, we can divide the problem into smaller parts (i.e. modules) and solve them

one by one.

2. Problem-solving procedure

Before analyzing, we have to know exactly what the problem is. So, the first step is:

1. Problem Identification

After that, we should do

2. Problem Analysis

Then, make a draft framework

3. Algorithm Design

Then, try to solve the problem by

4. Developing a Solution

Now, we have a solution, but we are not sure it is workable or not, so, we should perform

5. Debugging and Testing

Finally, a solution is developed, but it is not the end, to make improvement become smooth, we should

remarks any

6. Documentation

Algorithm Design –

In the state of Algorithm Design, Pseudocode and Flowchart are two commonly used techniques

to do the algorithm.

` will have no standard format (syntax) and so a segment of Pseudocode will have no syntax

error but logical error only.

What is syntax error?

JavaScript is a programming language with standard format, so it may result syntax error. E.g.

X = 10;

Y = 20;

Y = 2X;

2X = Y 3;

Syntax error / logical error

How to fix?

document.output(“Who are you?”); Syntax error / logical error

How to fix?

1

i.e. Source program Compiler Object program

High level programming language is the programming language that human being can

understand, example include JavaScript, Java, C++, Pascal, etc.

But for computer, it can only recognize machine code like 10010101 represents delete file, or

11001010 represents create folder, etc. However, since each machine code may be different for

different OS (operating system), so, Low level programming language is not portable / compatible.

A compiler is a software program that it will translate a high level programming language into a

machine language. So, a compiler should usually be platform oriented (machine dependent).

And so, an executable file should be built according to the OS of the computer. So, an executable

file should not be portable but the high level programming language may be portable.

Conclusion:

1. Error

- a violation of the grammatical rule of a programming language

- can be checked by the

- eg: wrong spelling of some reserved word, using an unknown variable

2. Error

- it occurs when a program terminates abnormally

- eg: division by zero, out of memory

3. Error

- it is mainly caused by an incorrect

- it produces an result

- it be detected by the translator / compiler

- eg: the calculated average mark of a test is greater than 100

Pseudocode Sample 1:

SET total to zero

REPEAT

READ Temperature

IF Temperature > Freezing THEN

INCREMENT total

END IF

UNTIL Temperature < zero

Description of the program:

3

Print total

Pseudocode Sample 2:

Input a number N

X <- 1

WHILE (X < N) AND (N < 5)

X <- X + 2

END

Output X, N

State the output of the program with input as

(i) 4

(ii) 14

Remember, there is no specific syntax for Pseudocode and so it will have no syntax error.

Note that in writing program, logical comparison is very useful and important. Below show some

operations:

X = TRUE; Y = FALSE;

NOT X NOT(NOT Y) X and Y NOT X AND NOT Y (X OR NOT(X AND Y))

TRUE

FALSE

Flowchart is a way to represent the logic and actions of an algorithm graphically.

Flowchart Sample:

Developing a Solution –

It is a top-down approach that divides a complex solution into some manageable subprograms

(module).

To develop a solution, usually we would create a program based on algorithm in “algorithm

design” stage. That is, the output of this stage is a computer program. Below shows two simple

programs in JavaScript:

4

Exercise:

1. The purpose of adding comments to a program is

A. to evaluate the program. B. to increase functionality.

C. to increase the speed of the program. D. to assist program maintenance.

2. The purpose of using meaningful variable names in a program is

A. to make the program more readable.

B. to increase the program development time.

C. to help translating programs into machine codes.

D. to test the program more thoroughly.

Debugging and Testing

It is a checking process. Here, “Debugging” refers to the process of locating and fixing defects in a

program. “Testing” is to ensure a program works and is free of error.

To test a program, the program itself should have already compiled successfully. That is, it will not

contain any syntax error. So, basically, testing focuses mainly on finding out logical errors and run-

time error.

To discover logical error, we should test the program with relevant input data and check whether

it will give correct output data.

To discover run-time error, then, should we just test the program with relevant input data? Yes /

No

If No, then, what else should be used as the input data? Give an example to support your answer.

Documentation

It aims to describe in detail what a certain program is for and how it is designed, developed and

tested. Although documentation appears at the last stage of the problem-solving procedure, it

should be carried out throughout the whole process.

6

There are two main categories of written documentation for computer programs: user manuals

and program manuals.

Function of documentation:

It can help programmers maintain the program in the future.

Other programmers may have to maintain the program or make changes to it at a later time.

It helps programmers discover errors in the program.

Users can learn how to use the program through a user manual like

how to install

what functions are provided by the program

how to handle a particular task, etc.

Introduction to Algorithm Design

Flowchart symbolsBegin / End

Process

Input / Output

Decision

Pre-defined Process

Decision box: It has two common features. One is Branching and the other one is Looping.

Branching / IF / Conditional Statement Looping

7

START END

New <- New + 1

Input X, Y

Output X

Y = X ?

Yes

No

Find the remainder (R) of Y divided by X

Yes

Exercise 1: Arrange the following flowchart symbols to form a program that can determine whether an

inputted data is an odd number or an even number.

Exercise 2: Arrange the following flowchart symbols to form a program that can find the maximum

divisor of a number. (Examples: 27 = 3x9, so, 9 would be the maximum divisor.)

To achieve the goal, we should think how to find a maximum divisor by ourselves. That is, what is the

algorithm in our own brain to find the maximum divisor?

Take 27 be the example, the step to find the maximum divisor would be:

Step 1:, Divide 27 by 2, check the remainder.

Step 2: If remainder=0, then 2 would be a divisor.

Step 3: Divide 27 by 3, check the remainder.

Step 4: If remainder=0, then 3 would be a divisor.

Step 5: Do the steps above again and again until it reaches 26 (27 – 1) to find all the divisors.

Step 6: Output the maximum divisor.

To investigate the above steps, you will see it is in fact not 6 steps. It is like infinite steps it does 3 main

steps over and over again. These 3 main steps would be:

1: Runs a counter (like 2, 3 and so on) from 2 to 27 – 1.

2: Divide 27 by the counter and check the remainder.

3: Store the divisor when found one.

These 3 main core steps involve repeated operations, we called looping or

Iteration. The structure of a looping by flowchart is shown on the right:

8

START

END

Find the remainder (R) of X divided by 2

?Yes

No

Y = X ?

No

Y = X ?

Yes

No

Finish the following flowchart so that it

runs a counter from 2 to 27 – 1. It is what

we called a FOR-LOOP.

In JavaScript, it is

For ( ) {

…….}

Finish the following flowchart so that it can let users input a number, then it will output the maximum

divisor.

9

X=2

Yes

No

START

Find the remainder (R) of Y divided by X

END

Exercise 3: Create a flowchart so that it can find the H.C.F. of two inputted numbers.

10

START

Input X, Y

END

In JavaScript, we can find the H.C.F. in the following manner:

<script language= "JavaScript">function findHCF() {var data1 = parseInt(num1.value); //parseInt() is a JavaScript functionvar data2 = parseInt(num2.value); //to find the value of a text string

if (data1 < data2) { min = data1;}else {min = data2;}

HCF_found = false;for (i=2;i<=min;i++) {

R1 = data1 % i;R2 = data2 % i;if (R1 == 0 && R2 == 0) {

HCF = i;HCF_found = true;

}}

if (HCF_found) {alert (HCF) }

else { alert("No HCF found!");}}</script>

<body>First Number:<input type=text name=num1><br>Second Number:<input type=text name=num2><input type=button value=HCF onClick=findHCF()></body>

FOR– Loop

For (i=1;i<10;i++) {

Alert(i);

}

WHILE – Loop

11

Yes

No

Comment

i = 0;x = “Numbers include ”;while (i<5) { x = x + ", " + i; i++;}x = x + “ and “ + i + “.”document.write(x);

For the following two flowcharts, dry run them with the input 3 and 5 respectively.

(i) (ii)

X = 3 Output =

No. of iteration =

Output =

No. of iteration =

X = 5 Output = Output =

ProcessYes

No

Input X

S = 1N = 2

S = S + N

N = N + 1

N < X?

Output N

Input X

S = 1N = 2

S = S + NN = N + 1

N < X?

Output N

YES

YES

12

Yes

No

?

No. of iteration = No. of iteration =

Description of the flowchart:

REPEAT UNTIL Loop

With respect to the diagram on the right,

(i) how many iterations will it make?

(ii) what is the value of S at the end of the process?

(iii) what is the value of I at the end of the process?

(iv) how to modify the iterations so that it will find the

summation of all the multiplications of 3 between 0 and 100?

Common programming techniques:

1. Swapping data:

The following program codes is supposed to exchange the data between X and Y. What would be

the output and how to fix it?X = 3 ;Y = 5;X = Y;Y = X;

After the end of this program, X = and Y = .

The correct program code would be:

2. Summation from 1 to 100:

We can find the summation of 1 to 100 easily by a FOR-LOOP.

Process

No

Yes

?

13

I = 1S = 0

S = S + I

I > 10?

I = I + 3No

1

2

3

4

What is the different between a WHILE LOOP and a REPEAT UNTIL LOOP?

sum = 0;

for (i=1;i<100;i++) {

sum = sum + i;

}

The question is should it be

(i) for (i=1;i<100;i++) OR (ii) for (i=1;i<=100;i++) ?

What is the value of i in (i) and (ii) respectively?

3. Multiplication from 1 to 10.Investigate what is wrong in the codes below:

result = 0;

i = 1;

While (i<10) {

Result = result * i;

i = i + 1;

}

Modification :

4. To output the absolute value of an input X.

if (X > 0) {

Y = }

Else { Y = }

X = ;

5. Data type problem, suppose

var X = ‘a’;

var Y = 10;

var Z = ‘c’;

What would be the result of the following?

(i) Z = X + Z;

(ii) Y = Y – 5.78;

(iii) Z = X + Y;

Advance Techniques:

1. Array + Passing variables (http://www.yll.edu.hk/cs/resources/ict/htm/javascript/reOrder.htm)<script language= "JavaScript">function ReOrder(number) { //pass a number to this function.

var myArray = new Array(); //create a new arraylimit = number;

14

for (i=0;i<limit;i++) {counter = i + 1;statement = "Enter name " + counter + ":" ;response = window.prompt(statement,"");myArray[i] = response; //store the response into the array

}

document.write ("Original array is shown below:<br>");for (i=0;i<limit;i++) { document.write(myArray[i]+"<br>");}document.write ("The sorted array is shown below:<br>");myArray.sort();for (i=0;i<limit;i++) { document.write(myArray[i]+"<br>");}

}</script><body>Input different names and it will sort them to give you an ascending list.<br><input type=button value="3 numbers" onClick="ReOrder(3)"><input type=button value="5 numbers" onClick="ReOrder(5)"><input type=button value="7 numbers" onClick="ReOrder(7)"></body>

2. Modular Approach

A program may contain thousands lines of codes or more. So, smaller modules have to be adopted to

form a real life program. The process of splitting up a whole program into modules is called “Modular

approach”. Below shows a sample program that contains modules. Try to discover what the advantages

of using modular approach are. (http://www.yll.edu.hk/cs/resources/ict/htm/javascript/doFraction.htm)function findHCF(data1, data2) {

if (data1 < 0) { data1 = -data1}if (data2 < 0) { data2 = -data2}

if (data1 < data2) { min = data1;}else {min = data2;}

HCF_found = false;for (i=2;i<=min;i++) {

R1 = data1 % i;R2 = data2 % i;if (R1 == 0 && R2 == 0) {

HCF = i;HCF_found = true;

}}if (HCF_found == false) {

HCF = 1}return HCF;}

function findLCM(x,y) {value1 = parseInt(x.value);value2 = parseInt(y.value);

LCM = 1;

HCF = findHCF(value1, value2);if (HCF != 1) {

LCM = LCM * HCF;value1 = value1 / HCF;value2 = value2 / HCF;

} LCM = value1 * value2 * HCF;return LCM;

}

function showLCM(In1, In2) {lcm = findLCM(In1, In2);alert (lcm);

}function DoFraction(N1, D1, N2, D2, operation) {

LCM = findLCM(D1, D2);

Numerator1 = parseInt(N1.value);Numerator2 = parseInt(N2.value);Denominator1 = parseInt(D1.value);Denominator2 = parseInt(D2.value);

Denominator = LCM;if (operation == '+') {

Numerator = Numerator1*LCM/Denominator1 + Numerator2*LCM/Denominator2;

15

} else {Numerator = Numerator1*LCM/Denominator1 -

Numerator2*LCM/Denominator2;}

Fraction31.value = Numerator;Fraction32.value = Denominator;

HCF = findHCF(Numerator, Denominator);Fraction41.value = Numerator / HCF;Fraction42.value = Denominator / HCF;

}

<body>Calculator 1: Finding LCM<table width=700><tr height=100><td width=200>Number 1:<input type=text name="input1" size=5></td><td width=200>Number 2:<input type=text name="input2" size=5></td><td><input type="button" value="Find LCM" onClick="showLCM(input1,input2)"></td></table>

Calculator 2: Fraction summation<table width=500><tr height=100><td width=60><table><tr><td><input size=5 name="Fraction11"></td></tr><tr><td><hr></td></tr><tr><td><input size=5 name="Fraction12"></td></tr></table></td><td width=15>+</td><td><td width=60><table><tr><td><input size=5 name="Fraction21"></td></tr><tr><td><hr></td></tr><tr><td><input size=5 name="Fraction22"></td></tr></table></td><td><input type=Button onClick="DoFraction(Fraction11,Fraction12,Fraction21,Fraction22,'+')" value="Summation of fractions"></td></table>

<table><tr bgcolor="yellow"><td width=100>The result is:</td><td width=60><table><tr><td><input size=5 name="Fraction31"></td></tr><tr><td><hr></td></tr><tr><td><input size=5 name="Fraction32"></td></tr></table></td><td width=15> OR </td><td width=60><table><tr><td><input size=5 name="Fraction41"></td></tr><tr><td><hr></td></tr><tr><td><input size=5 name="Fraction42"></td></tr></table></td></tr></table></body>

16

From the above program code, we can discover that modular approach should be used:

1. when some standard procedures are frequently used.

2. because of easier debugging / understanding of the program

3. because of effective division of labour (i.e. each programmer can focus on particular task.)

4. for large scale project so that it can be divided into manageable size modules.

17

Exercise:

1. Which of the following statements consist of

syntax errors?

(1) x + 1 4

(2) x 5 + 8 * 2

(3) x "5" + 5

A. (1) only B. (3) only

C. (1) and (3) only D. (2) and (3) only

2. Which of the following will give a true result?

A. (x > x + 5) AND (1 > 2)

B. (3 > -7) OR (-7 > 3)

C. (5 >= 5) AND (4 >= 5)

D. (7+3 < 8) OR (-7 > -6)

3. Consider the following program:INPUT xIF x > 5 THEN

X 5END IF

The purpose of the program is to

A. allow 5 to be entered only.

B. allow numbers less than or equal to 5 to

be entered only.

C. ensure that the value of X is greater than

5.

D. ensure that the value of X is less than or

equal to 5.

4. How many times will the following WHILE-loop

iterate?i 6WHILE i <10 DO

…i i + 1

END WHILEA. 0 B. 4

C. 5 D. 6

5. How many times will the following REPEAT…

UNTIL-loop iterate?i 6REPEAT

…

i i + 1UNTIL i > 10

A. 0 B. 4

C. 5 D. 6

6. Which line of the following pseudocode

segment can be deleted without affecting the

result?

Line number Statement

10 C = 60

20 E = 70

30 M = 80

40 T = 95

50 M = M – T

60 INPUT C

70 C = C + E

80 OUTPUT (C + E)

90 OUTPUT M

A. Line 10 B. Line 20

C. Line 30 D. Line 40

7. An algorithm (算法) is

A. a program

B. a set of steps used to solve a problem

C. a description of how the problem has

been solved

D. a clear diagram showing the existing

problem

8. In a report card, the average mark of a student

is outputted as -20. What kind of error is it?

A. syntax error B. run-time error

C. logical error D. printing error

9. Which of the following is/are advantage(s) of

compiler over interpreter?

(1) Compiled programs run faster

(2) Source codes need not be present during

execution.

18

(3) Compiled programs are easier to develop.



10. Object programs are free of

(1) syntax errors (2) runtime errors

(3) logical errors


C. (1) and (2) only D. (1), (2) and (3)

11. Which of the following would lead to a logical

error?

(1) A “>” sign is mistyped as “<” in a

conditional statement

(2) The assignment statement x x + 1 is

mistyped as x x + 2

(3) The reserved (保留字) word “if” is

mistyped as “fi”.



12. Which of the following is/are high level

language(s)?

(1) JAVA (2) PASCAL

(3) machine language



13. Which of the following is machine

independent?

A. assembler

B. assembly language

C. machine language

D. C source programs

14. Consider the following program:

10 P 1

20 FOR i =6 to 8 DO

30 P P * i

What is the value of P just before the

execution finishes?

A. 21 B. 42

C. 48 D. 336

15. Debugging is to

A. find out any hidden errors

B. make corrections to the program so that it

is error free

C. kill any bugs or bacteria

D. kill a virus using an anti-virus software

16. Documentation

A. describe what has been done and how the

problem is solved

B. use a word processing software to

produce a document

C. write a letter to the clients telling them the

problem is solved

D. re-write the program t make it more

versatile.

17. If we are going to add up all the even numbers

from 1 to 100, which of the following

constructs is most likely to be adopted?

A. Looping B. Branching

C. Sequencing D. Sorting

18. What does a compiler do?

A. A compiler translates a program written in

a high-level language into machine-

executable instruction.

B. A compiler debugs errors found in a

program written in a high-level language.

C. A compiler translates high-level language

into an intermediate form, which is then

executes.

D. A compiler makes a program written in a

high-level language run on a computer.

19. Which of the following is the initial step in

19

problem solving?

A. Designing an Algorithm

B. Problem Analysis

C. Problem Identification

D. Documentation

20. Which of the following is/are advantage(s) of

breaking a problem into smaller tasks?

(1) Programs are easier to develop.

(2) Programs are easier to debug.

(3) Programs are faster.

A. (1) only B. (1) and (2) only

C. (2) and (3) only D. (1), (2) and (3)

21. An algorithm is

A. a computer program.

B. a set of ordered steps used to solve a

problem.

C. a definition of problem.

D. a graphical representation of the steps.

22. Pseudocodes may consist of

(1) assignment statements

(2) conditional statements

(3) variable type definition



23. Which of the following errors are usually

discovered the earliest in program

development?

A. syntax errors B. logical errors

C. runtime errors D. data errors

24. Which of the following errors are usually

discovered by using test data?

(1) syntax errors (2) logical errors

(3) runtime errors



25. Which of the following belong(s) to runtime

errors?

(1) division by zero (2) out of memory

(3) using a reserved word as variable name



26. Which of the following would lead to a logical

error?

(1) A ">" sign is mistyped as "<" in a

conditional statement.

(2) The assignment statement x <- x + 1 is

mistyped as x<- x+2.

(3) The reserved word "if' is mistyped as "fi".



27. If there is no testing, a computer program may

contain

(1) bugs. (2) viruses.

(3) worms.

A. (1) only B. (1) and (2) only


28. Debugging means

A. correcting mistakes in a program.

B. writing comments for a program.

C. removing small insects from a computer.

D. converting an algorithm into a program

flowchart.

Questions 29 to 31:

Consider the following algorithm:

step 1 input x

step 2 if x > 0 then

step 2.1 increase x by 1

else

step 2.2 decrease x by 1

20

29. Which of the following can replace Step 2.1?

A. x <- 1 B. x <- x - 1

C. x <- x + 1 D. x <- x + x

30. Step 2 represents

A. a for loop

B. a while loop

C. a conditional statement

D. an expression

31. If the input data is -5, what will be the value of

x?

A. -4 B. -5

C. -6 D. 5

32. Y = 5 * x - 5

Given that X is a number between 0 and 1

inclusively. What is the range of Y?

A. between 0 and 1 inclusively

B. between -5 and 0 inclusively

C. between 0 and 5 inclusively

D. between 5 and 10 inclusively

33. Given that P = 6. What is the value of P after

line 20?

10 P <- P + 1

20 P <- P - 2

A. 4 B. 5

C. 6 D. 7

34. Given that P = 3 and Q = 5. What are the

values of P and Q after line 20?

10 P <- P + Q

20 P <- P - QP Q

A. 8 0 B. -2 5C. 3 5 D. 3 0

35. Given that P = 3 and Q = 5. What are the

values of P and Q after line 20?

10 P <- P * Q

20 P <- P/QP Q

A. 15 1 B. 3 5C. 3 1 D. 5 3

36. Given that P = 1.

10 P <- P * Q

20 P <- P * Q

30 P <- P * Q

What would be the result stored in P after line

30?

A. the value of Q B. the square of P

C. the square of Q D. the cube of Q


10 INPUT X

20 IF X >= 0 THEN Y <- 1

30 IF X < 0 THEN Y <- -1

Which of the following statements is true?

A. Y is always a positive number.

B. Y is the absolute value of X.

C. The product of Y and X is always a

positive number.

D. The product of Y and X is always a

negative number.


10 INPUT P, Q

20 IF 2*P - Q > 0 THEN

30 OUTPUT P

40 ELSE

50 OUTPUT Q

60 ENDIF

If the input data are 5 and 10, the output will

be

A. P B. Q

C. 5 D. 10

21

39. The following program finds the reciprocal of

an input number:

100 INPUT X

200 OUTPUT 1/X

Which of the following lines should be added

to avoid division by zero error?

A. 50 IF X < 0 THEN GOTO 100

B. 150 IF X < 0 THEN GOTO 100

C. 150 IF X <= 0 THEN GOTO 100

D. 150 IF X = 0 THEN GOTO 100

40. Given that P = 1 and Q = 2. Which of the

following logical expressions is TRUE?

A. (P>1) AND (Q>2)

B. (P > 1) OR (Q > 2)

C. (P >= 1) AND (Q > 2)

D. (P >= 1) OR (Q > 2)

41. Given that p and q are boolean variables

storing TRUE and FALSE respectively. Which

of the following expressions is FALSE?

A. p OR q

B. (NOT p) AND q

C. p OR (NOT q)

D. (NOT p) OR (NOT q)

42. Which of the following logical expressions is

TRUE?

A. (NOT (6 > 3)) AND ((4 < 2 + 1) OR (2 + 3

> 1) )

B. NOT ((2 + 3 >= 5) OR (7 - 9 < 2) )

C. (NOT (7 - 3 < 3) ) AND (NOT (3-1 < -2))

D. (6 - 1 < 2) AND (NOT (1 > 2) OR (3 - 5 >

4) )

2006 CIT#28

43. Which of the following characteristics of high

level language can reflect the concept of

program modules?

A. Subprogram B. Comment

C. Condition D. Looping

2005 CIT#25

44. Which line in the following pseudo-code

segment can he deleted without affecting the

result?

Line number Content

10 A = 30

20 B = 40

30 C = 50

40 D = 60

50 C = C – D

60 Input A

70 A = A + B

80 Output (A + B)

90 Output C

A. Line 10 B. Line 20

C. Line 30 D. Line 40

45. Consider the following program flowchart:The value of X and Y just before the end of execution are

X YA. 3 5B. 3 2C. 2 5D. 2 3

22

START

X 3Y 5

X>Y?

Y Y - X X X - Y

END

no yes

46. Consider the following program flowchart:The purpose of the flowchart is toA. find the sign of an input number.B. find the product of two numbers.C. find the absolute value of an input number.D. reverse the sign of an input number.

47. Consider the following program flowchart:

The purpose of the flowchart is to make sure that the input number isA. greater than zero.B. less than zero.C. less than or equal to zero.D. not equal to zero

48. Consider the following program flowchart:

The output will be A. 2B. 3 C. 5 D. -22

49. Consider the following program flowchart:The values of S and N just before the end ofexecution are

S NA. 0 0B. 42 12

23

START

Input X

X > 0?

Y –1 Y 1

X Y * X

END

yesno

START

Input X

X > 0?

X = 0?

END

yes

yesno

noSTART

P 27Q 5

P >Q?

P P – Q

Output Q – P

END

Yes

No

START

S 0N 0

S < 50?

N N+2S S+N

END

YesNo

C. 50 12D. 56 14

2005 CIT#2750. Study the following flowchart.

If the input value is 0, what is the output value?A. 0B. 8C. 10D. 12

2006 CIT#3251. Study the following flowchart.

If six numbers, 1, 4, 3, 2, 8 and -1 are to be subsequentlyinput, what will be the final value of S?A. 5B. 13C. 15D. 18

200 7 CIT# 28 52. What is the purpose of the above flowchart?

A. Count the numbers between 1 and XB. Find (1+2+3+…+X).C. Find (1+2+3+…+X)/X.D. Count the number of input values before -1 is entered.

200 8 CIT# 30 53. Consider the following flowchart.

Which of the following values will never be displayed?A. -4 B. 0C. 6 D. 8

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Conventional Questions:

1. Determine the number of 1’s printed in each of the following programs:(a) (b) (c)

10 X 0 10 X 1 10 X 120 OUTPUT 1 20 OUTPUT 1 20 IF X < 5 THEN30 X X + 1 30 X X + 1 30 X X + 140 IF X <= 5 THEN 40 IF X < 5 THEN 40 OUTPUT 150 GOTO 20 50 GOTO 20 50 GOTO 2060 END IF 60 END IF 60 END IF

No. of 1’s = No. of 1’s = No. of 1’s =

2. Determine the output of the following programs:(a) (b) (c)

10 X 2 10 X 2 10 X 220 FOR i = 2 to 8 20 REPEAT 20 WHILE X < 2030 X X + 3 30 X X + 1 30 X X + 340 i = i +1 40 UNTIL X > 20 40 END WHILE50 OUTPUT X 50 OUTPUT X 50 OUTPUT X

Output = Output = Output =

3. The following program is designed to find the sum of 12 + 22 + 32 + … + 102 .

S 0__________________________

________________________________________________________

OUTPUT S

4. (a) The following program is for validation of two input, x and y.

_____________INPUT xINPUT y

____________________________

(b) Should the programmer use Repeat-Loop or While-Loop? Why?

25

Program Flowchart:

Program Flowchart:

5. The following program is for adding all positive number inputted by the user. When the user finished inputting and want to calculate the result, he/she can input –1 to terminate the program.SUM 0_________ ____________________ ______

INPUT xSUM = _______________________

______ _________________

6. Consider the following program segments:(a) (b) (c)

10 X 10 10 X 10 10 S 1020 S 100 20 S 100 20 S S / 230 IF X <2 THEN 30 IF 2*X < 15 THEN 30 IF S/2 > 2.5 THEN40 S S – 10 40 S S / 10 40 S S / 250 ELSE 50 ELSE 50 ELSE60 S S + 10 60 S S * 10 60 S S * 270 END IF 70 END IF 70 END IF

S = S = S =

7. The following is a program to accept two inputs from the user and will arrange them into ascending order. Fill in the following blanks in pseudocode to finish the program segment.

INPUT XINPUT Y_______________________________

_____________________________________________________________________

______________OUTPUT XOUTPUT Y

8. The following is a program to accept an input from the user and return the absolute value of the input to the user. Fill in the following blanks in pseudocode to finish the program segment.

INPUT X___________________________

_______________________

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Program Flowchart:

Program Flowchart:

Program Flowchart:

________________OUTPUT X

9. Consider the following program segment.10 S 020 X 030 X X + 140 S S + X50 IF X < 10 THEN60 GOTO 3070 END IF80 OUTPUT S

(a) What is the purpose of this program?(b) What is the output of this program?(c) If Line 50 is changed to “IF NOT(X >= 10) THEN”, will it have any difference on the

whole program segment? Explain.(d) Suppose we do not want to use the above Branching Statements to finish the above task

and would like to use Looping, fill in the following program segment to write the same program segment using WHILE-looping.S 0X 0_________________________________________________________________________________________________________________________________________________OUTPUT S

10. The following is a program segment written in pseudocode.x 4REPEAT

x x - 3UNTIL x < -20OUTPUT x

(a) What is the output of the program?(b) How many times will the statement inside the REPEAT…UNTIL loop run?(c) What is the characteristics of REPEAT…UNTIL loop compared to other looping method?

27

Program Flowchart:

Program Flowchart:

11. (a) Give an examples for each of the following errors(i) syntax error(ii) runtime error(iii) logical error

(b) Explain why a programmer should test a program with both(i) valid data, and(ii) invalid data

12. What are the outputs of the following flowchart?

X = ____________________________

Y = ____________________________

13. Consider the following programming flowchart:

State the output from the program if the inputs are:(a) 10, 20, 60, 10, 20

(b) 120, 130, -2, 200

28

2006 CIT#MC34 (Modified)14. The following algorithm is used to calculate the average mark of students with a sequence of

input mark until a negative value to end the input process. Study the following algorithm and answer the following questions.10 INITIALIZE the counter to zero20

30

40 DO WHILE

50 ACCUMULATE total60 INCREMENT the counter70 READ a mark from the input80 END DO LOOP90 CALCULATE the average by dividing total by the counter

a) Please fill in the blanks in the above algorithm to complete the program.b) State the situation that this algorithm design will create run-time error.

c) The above algorithm is done by using Pseudocode, other than this approach what else technique can be used to design an algorithm?

d) After the algorithm design stage finished, programmer can starting doing the developing a solution by writing a program. Below shows some program codes:

i = 0;…while (x >= 0) {

t = t + x;…

}ave = t / i;

Give two suggestions to the above program.

29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20C B D B C A B C C A C C D D B A A A C B

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40B C A D C C A A C C C B B C B D C D D D

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60B C A A B C B B D D A D D

1. (a) 6 (b) 4 (c) 4

2. (a) 23 (b) 21 (c) 20

3. S 0For i = 1 to 10 do

S S + i * iOUTPUT S

4. (a) RepeatINPUT XINPUT Y

Until (X > 0) AND (Y > 0)

(b) Repeat loop. Because the input procedure should be executed at least once. Statements inside a Repeat-Loop are executed at least once, which satisfy the condition.

5. SUM 0While x <> -1 do

INPUT xSUM = SUM + x

End while

6. (a) S = 110 (b) S = 1000 (c) S = 10

7. INPUT XINPUT YIf X > Y then

Z X

30

X YY Z

End IfOUTPUT XOUTPUT Y

8. INPUT XIf X < 0 then

X -1 * XEnd IfOUTPUT X

9. (a) 1 + 2 + 3 + … + 10 / Calculate the consecutive numbers from 1 to 10.(b) 55(c) No. Logically, NOT (X >= 10) is equivalent to X < 10.(d) S 0

X 0While X < 10 do

X X + 1S S + X

End whileOUTPUT S

10. (a) -23(b) 9(c) Statements inside repeat-loop are executed at least once.

11. (a) (i) 5 x(ii) division by zero / out of memory(iii) the average mark is greater than 100

(b) (i) to make sure that it would give expected result(ii) to make sure that it would trap (找出) the error

12. x = 5, y = 1

13. (a) 110(b) 148

14. Refer to the hidden text.

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computer network - yll.edu.hk · web viewthere are several data type in programs. they include:...

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