midterm exam review

Midterm ExamReview

Program Design (I)2021 Fall

Fu-Yin CherngDept. CSIE, National Chung Cheng University

Please Notice

● This is just a quick review of the previous lesson● This doesn’t mean that the questions of the midterm exam will be only from

the contents of these slides● The purpose of these slides is to let you know where are the important parts

in each chapter which related to the midterm exam

Ch 2. C Fundamentals

Variables and Types

● The locations to store data are called Variable ● Every variable must have a type, which specifics what kind of data it will store● Wide variety of types, e.g., int and float.

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data

variable

int: 1, 2, 10, 1000

float: 0.1, 0.01, 10.129

Assignment

● Now, we have declared variable for later use, how to store data in the variables?

● We give a value to a variable by assignment

● Don’t assignemt before declaration● Assign the correct type of data to

the variable○ mixing type might cause some problems

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int height, length, width, volume;float profit, loss;

height = 8;length = 12;width = 10;profit=2150.48;profit=2150.48f;//a better version

height = 8.1 //mixing type

Printing the Value of a Variable

● printf can be used to display the current value of a variable.● To write the message:

○ where h is the current value of the height variable● We use the following call

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Height: h

printf("Height: %d\n", height);

%d is a placeholder indicating where the value of height is to be filled in.

Reading Input

● scanf is the C library’s counterpart to printf.● scanf requires a format string to specify the appearance of the input data.

○ f for printf and scanf stands for ”formatted”○ printf and scanf required format string to specify the input/output data (the shape of data)

● The & symbol is usually (but not always) required when using scanf○ hard to explain the meaning of & now, so just remember to add it when using scanf

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printf("Height: %d Length: %d\n", height, length);

scanf("%d", &i);

tell the printf that that output data is two integar (%d)

reads an integer (%d); stores into i users will input data

Ch 3. Formatted I/O

The pintf Function

● A conversion specification is a placeholder representing a value to be filled in during printing.

○ %d is used for int values○ %f is used for float values

● The information after % character specifies how the value is converted to printed form

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int x = 1;

printf("%d", x);

//%d specifies that printf is to convert an int value to a string of decimal digits

Conversion Specifications

● A conversion specification can have the form ● m and p are integer constants and X is a letter.

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%m.pX or %-m.pX


● Both m and p are optional; ● if p is omitted, the period (.) that separates m and p is also dropped.

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%mX or %-mX

%m.pX or %-m.pX


● For example● Can you identify where is the X, m, and p for each case?

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%10.2f

%10f

%.2f


● For example● Can you identify where is the X, m, and p for each case?

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%10.2f: m is 10, p is 2, and X is f.

%10f: m is 10 and p (along with the period) is missing, X is f

%.2f: p is 2 and m is missing, X is f.

Conversion Specifications - minimum field width

● m: minimum field width● specifies the minimum number of characters to print.● If the value to be printed requires fewer than m characters, it’s right-justified

○ Putting a minus sign in front of m causes left justification.● If the value to be printed requires more than m characters, the field width

automatically expands to the necessary size.

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int i=123;

printf("%4d", i); //output: •123 (• represents the space character.)

printf("%-4d", i); //output: 123•

printf("%2d", i); //output: 123 (auto expand)

Conversion Specifications - precision

● p: precision● the meaning of p depends on the choice of X, the conversion specifier.● For d specifier (display an integer in decimal form)

○ p indicates the minimum number of digits to display (extra zeros are added to the beginning of the number if necessary).

○ If p is omitted, it is assumed to be 1 (%d = %.1d)

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● For f specifier (display floating-point numbers)○ p indicates how many digits should appear after the decimal point (default is 6). ○ If p is 0, no decimal point is displayed.

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● e specifier○ Display a floating-point number in expenetial formate (scientific notation)

● For e specifier○ p indicates how many digits should appear after the decimal point (default is 6). ○ If p is 0, no decimal point is displayed○ same as the meaning of p for f specifier

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Ch 4 Expression

Summary

● Operators○ arithmetic, assignment, relational, logial, and many others (in later chapters)

● Arithmetic Operators○ Operator Precedence and Associativity

● Assignment Operators○ Simple and Compound assignment

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Expression Evaluation

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Precedence Name Symbol Associativity

1 (high) increment (postfix) variable++ left

decrement (postfix) variable--

2 increment (prefix) ++variable right

decrement (prefix) --variable

unary plus +variable

unary minus -variable

3 multiplicative * / % left

4 additive + - left

5 (low) (compound) assignment = *= /= %= += -= right

Ch 5. Selection Statements

Relational Operators

● These operators produce 0 (false) or 1 (true) when used in expressions.● The relational operators can be used to compare integers and floating-point

numbers, with operands of mixed types allowed.

int i;

i = 1 < 2.5; // i is 1 (true)

i = 5.6 < 4; // i is 0(false)

Symbol Meaning

< less than

> greater than

<= less than or equal to

>= greater than or equal to

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Equality Operators

● How about we want to check if i is equal to j?● two equality operators● The equality operators are produce either 0 (false) or 1 (true) as their result.● The equality operators have lower precedence than the relational operators

Symbol Meaning

== equal to

!= not equal to

i < j == j < k;

(i < j) == (j < k);

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Logical Operators

Symbol Meaning Usage Result

! logical negation (unary) !TRUE!FALSE

FALSETRUE

&& logical and (binary); AND TRUE && TRUEFALSE && TRUEFALSE && FALSE

TRUEFALSEFALSE

|| logical or (binary); OR TRUE | | TRUEFALSE | | TRUEFALSE | | FALSE

TRUETRUEFALSE

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Logical Operators

● The logical operators also produce 0 (false) or 1 (true) as their result.● The logical operators treat any nonzero operand as a true value and any zero

operand as a false value.

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Logical Operators

● && and || first evaluate the left operand, then the right one● If the value of the expression can be determined from the left operand alone, the

right operand isn’t evaluated.● (i != 0) is evaluated first. If i isn’t equal to 0, then (j / i > 0) is evaluated.

○ if (j / i > 0) is false, this expression is false● If i is 0, the entire expression must be false, no need to evaluate (j / i > 0)

○ avoid the division by zero

(i != 0) && (j / i > 0)

//if left operand is true, then run right

left operand right operand

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The else Clause

● An if statement may have an else clause● The statement that follows the word else is executed if the expression has

the value 0 (False).

if (i > j)

max = i;

else

max = j;

if i is less than or equal to j, the value of i > j will be 0 so that the else is executed

if i is larger than j, the value of i > j will be 1 so that the statement inside if is executed

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Cascaded if Statements

● Although the second if statement is nested inside the first, C programmers don’t usually indent it. Instead, ...

if (n < 0)

printf("n is less than 0\n");

else if (n == 0)

printf("n is equal to 0\n");

else

printf("n is greater than 0\n");

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Conditional Expressions

● “if expr1 then expr2 else expr3”● The expression is evaluated in stages● expr1 is evaluated first; ● if its value isn’t zero (true), then expr2 is evaluated, and its value (expr2) is

the value of the entire conditional expression.● If the value of expr1 is zero (false), then the value of expr3 is the value of

the conditional expression

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expr1 ? expr2 : expr3

nonzero (true)

zero (false)

The switch Statement

● The switch statement ● switch statement will test the

value of grade variable ● If match 4, executed the

statements in case 4○ print “Excellent”○ break statement makes the

execution flow jump out of the switch statement

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switch (grade) {

case 4: printf("Excellent");

break;

case 3: printf("Good");

break;

case 2: printf("Average");

break;

case 1: printf("Poor");

break;

case 0: printf("Failing");

break;

default: printf("Illegal grade");

break;

}

...

if grade == 4

Ch 6. Loops

The while Statement

● The easiest way to set up a loop● below is the general form of the while statement● expression: controlling expression

○ expression to control if the loop will stop or continue● statement: loop body

○ If the expression is true the loop continues to execute

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while ( expression ) statement

The while Statement

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i = 1;

while (i < n) /* controlling expression; n will be given by users */i = i * 2; /* loop body */

statement value of i controlling expression action

i = 1; 1 i < n? Yes; continue.

i = i * 2; 2 i < n? Yes; continue.



i = i * 2; 16 i < n? No; exit from loop

n = 10

The for Statement

● Example

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for ( expr1 ; expr2 ; expr3 ) statement

for (i = 10; i > 0; i--)

printf("%d\n", i);

for Statement Idioms

● The for statement is usually the best choice for loops that “count up” (increment a variable) or “count down” (decrement a variable).

● A for statement that counts up or down a total of n times will usually have one of the following forms (idioms)

● Imitating these patterns is helpful to avoid some of the following errors

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Counting up from 0 to n–1 for (i = 0; i < n; i++)

Counting up from 1 to n for (i = 1; i <= n; i++)

Counting down from n–1 to 0 for (i = n - 1; i >= 0; i--)

Counting down from n to 1 for (i = n; i > 0; i--)

The break Statement

● The break statement can transfer control out of a switch, but it can also be used to jump out of a while, do, or for loop.

● A loop that checks whether a number n is prime can use a break statement to terminate the loop as soon as a divisor is found

● exit from break: n isn’t prime● exit from for: n is prime

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for (d = 2; d < n; d++){

if (n % d == 0)

break;

}

if (d < n){

printf("%d is divisible by %d\n", n, d);

} else{

printf("%d is prime\n", n);

}

exit the loop when find a divisor is found

The continue Statement

● Example of continue● read a series of numbers and

computes their sum● the loop terminates when 10

nonzero numbers have been read○ so 0 is not counted

● if 0 is read, skipping the rest loop body but remaining inside the loop○ so n will not be increased by 1 if

input is 0

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n = 0;

sum = 0;

while (n < 10) {

scanf("%d", &i);

if (i == 0){

continue;

}

sum += i;

n++;

/* continue jumps to here */

}

Ch 7. Basic Type

39https://justdocodings.blogspot.com/2018/03/c-data-types.html

long long intlong long int

Character Types

● Today’s most popular character set is ASCII○ American Standard Code for Information Interchange

● a 7-bit code capable of representing 128 (27) characters.● ASCII is often extended to a 256-character code known as Latin-1 that provides the

characters necessary for Western European and many African languages.

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7-bit code

Operations on Characters

● When a character (char) appears in a computation, C uses its integer value.● Consider the following examples, which assume the ASCII character set:

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char ch;

int i;

i = 'a'; /* i is now 97 */

ch = 65; /* assign value to char, ch is now 'A' */

ch = ch + 1; /* ch is now 'B' */

ch++; /* ch is now 'C' */

Reading & Writing Using getchar and putchar

● getchar is useful in loops that skip characters as well as loops that search for characters.

● A statement that uses getchar to skip an indefinite number of blank characters:● When the loop terminates, ch will contain the first nonblank character that getchar

encountered.

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char ch;

while ((ch = getchar()) == ' ');

putchar(ch);

The Usual Arithmetic Conversions

● Two general Strategies of usual arithmetic conversions

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The type of either operand is a floating type

Neither operand type is a floating type

long double

double

float

unsigned long int

long int

unsigned int

int int

Conversion During Assignment

● Assigning a floating-point number to an integer variable drops the fractional part of the number

● Assigning a value outside the range of the variable’s type to a variable is meaningless

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int i;

i = 842.97; /* i is now 842 */

i = -842.97; /* i is now -842 */

i = 1.0e20; /*** WRONG ***/

Casting

● Although C’s implicit conversions are convenient, we sometimes need a greater degree of control over type conversion.

● For this reason, C provides casts.● A cast expression has the form

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( type-name ) expression type-name specifies the type to which the expression should be converted.

Casting

● Cast expressions also let us force the compiler to perform conversions.● To avoid truncation during division, we need to cast one of the operands:● Casting dividend to float causes the compiler to convert divisor to float

also.

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float quotient;

int dividend = 3, divisor = 2;

quotient = dividend / divisor; // quotient is 1

quotient = (float) dividend / divisor; // quotient is 1.5

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