ECE 264Object-Oriented

Software Development

Instructor: Dr. Michael GeigerSpring 2009

Lecture 2: Basic C++ Programs

Lecture outline Announcements / reminders

Web page is now online:

http://www.cis.umassd.edu/~mgeiger/ece264/sp09.htm Additional lab notes/policies

If you have a laptop, please bring it 24 machines in lab, but 32 / 25 students in W / F sections

Remember: place a photo of yourself (photo.jpg) in your M:\drive

(Quick) Pretest review Basic C++ programs

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Pretest review Pretest intended to review the following

Control structures (if/else, switch, loops) Basic data types Array accesses C output

Pretest review: if/else statementsint x, y; 

.

.

. if (x < 5) {

y = x + 1;}else {

y = x – 2;} 

1. At the end of the if/else statement above, if x = 4, y is equal to: a. 1 b. 2 (1 person) c. 4 d. 5 (55 correct)

 2. Now, if x = 5, y is equal to: a. -2 b. 3 (55 correct) c. 5 d. 6 (1 person)

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Pretest review: loopsint x = 1;int i = 0;while (i <= 3) {

x = x * 2;i++;

} 

3. Fill in the blank: The body of the while loop executes ______ times. a. 2 b. 3 (7 people) c. 4 (49 correct) d. an infinite number of   4. The final value of x is: a. 2 (3 people) b. 3 (1 person) c. 8 (12 people) d. 16 (40 correct)  5. Which of the following is a for loop that can replace the while loop and produce the same result for x? a. for (i = 1; i < 4; i++) (14 people)b. for (i = 0; i < 3; i++) (4 people)c. for (x = 0; x <= 3; x++) (3 people)d. for (i = 3; i >= 0; i--) (35 correct)

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Pretest review: arrays, I/Oint A[5] = {0, 7, 13, 12, 5};for (i = 0; i < 5; i++) {

printf(“A[%d] + 3 = %d\n”, i, A[i] + 3);} 6. In the first iteration, the program will display the following text on the screen: 

a. A[%d] + 3 = %d\n (1 person)b. A[i] + 3 = A[i] + 3 (2 people)c. A[0] + 3 = 3 (53 correct)d. A[1] + 3 = 10

  7. The value of A[4] is: a. 4 (1 person) b. 5 (31 correct) c. 12 (19 people) d. non-

existent (5 people)

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Pretest review: switch statementsswitch (var) {case 0:case 1:

x = x + var;break;

case 2:x = x – var;

case 3:x = x * var;break;

default:x = var;

} Assume x always equals 5 at the start of the switch statement. What is the value of x at the end of the statement if: 8. var = 1? a. 1 (5 people) b. 4 (2 people) c. 5 (7 people) d. 6 (42 correct)  9. var = 2? a. 2 (8 people) b. 3 (39 people) c. 6 (7 correct) d. 7 (1 person)  10. var = 5? a. 0 (1 person) b. 5 (51 people) c. 10 (2 people) d. 25 (1 person)

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Basic C++ programs We’ll cover the following today

Basic structure of a C++ program Constants and variables Identifiers C++ operators Standard input and output

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Example program #1/* Simple C++ Program */

/* This program computes the *//* distance between two points. */#include <iostream> // Required for cout, endl.#include <cmath> // Required for sqrt()using namespace std;int main(){// Declare and initialize objects. double x1(1), y1(5), x2(4), y2(7), side1, side2, distance;// Compute sides of a right triangle. side1 = x2 - x1; side2 = y2 - y1; distance = sqrt(side1*side1 + side2*side2);// Print distance. cout << "The distance between the two points is " << distance << endl;// Exit program. return 0;}

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Comments Comments help people read code, but are

ignored by the compiler C++ (like C) has two types of comment

// Single line comments end at the end of a line /* Delimited comments start and end as shown

here and can span multiple lines. */ Good programming practice to

Start file with comment describing purpose Comment functionality of each section of code

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Preprocessor directives Provide instructions to the compiler that are

performed before the program is compiled. Begin with a # Example:

#include <iostream> The #include directive instructs the compiler to

include statements from the header file iostream.

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using Directive The using directive instructs the compiler to

use files defined within a specific namespace Namespaces allow us to declare different scopes

Example: using namespace std; std is the name of the Standard C++ namespace Including this line allows you to avoid specifying

namespace for every identifier in your headers Otherwise, cout would have to be std::cout, etc.

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Block of Code A block of code is defined by a set of curly braces {…}. Can contain comments and statements

Statements can end in semicolon (;) or be enclosed in braces (e.g. if) Example:

int main(){ //Block defines body of main function

double x1(1), x2(4), side1;side1 = x2 – x1;

cout << side1 << endl; return 0; // main()returns int value of 0} //end definition of main

Every C++ program must contain exactly one function named main()

C++ program solutions always begin execution in main()

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Constants and Variables Constants and variables represent memory

locations that we reference in our program solutions. Constants are objects storing specific data that can

not be modified. 10 is an integer constant 4.5 is a floating point constant "Side1" is a string constant 'a' is a character constant

Variables are memory locations that store values that can be modified. double x1(1.0), x2(4.5), side1;side1 = x2-x1;

x1, x2 and side1 are examples of variables that can be modified.

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Memory Snapshot

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#include<iostream>using namespace std;int main(){ double x1(1.0), x2(4.5), side1;

double x1

double x2

double side1

side1 = x2-x1;

double x1

double x2

double side1

cout << “side 1 has length: “ side1;

1.0

4.5

?

1.0

4.5

3.5

Output:side 1 has length: 3.5

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Common C++ Data Types

Keyword Example of a constantbool true

char '5'

int 25

double 25.0

string "hello" //#include<string>

C++ Identifiers Identifiers are used to name objects in C++. Rules for selecting valid identifiers:

Identifier must begin with a letter or underscore _ Identifiers consists of alphanumeric characters

and underscore character only An identifier can not be a reserved word Only the first 31 characters of an identifier are

used to distinguish it from other identifiers. C++ is case sensitive Good programming practice: choose

descriptive identifiers

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Declarations A declaration statement defines new identifiers and

allocates memory Can assign initial value in declaration Syntax: [modifier] data_type identifier_list; Examples:

double length(20.75), width(11.5), volume;int numberOfFeetInYard(3);const int MIN_SIZE = 0;

Text uses: identifier(initial_value) (C++ specific) Could just as easily use: identifier = initial_value

Good programming practices Grouping declarations together for similarly used variables or

using 1 per line allows you to comment them meaningfully Separate declarations from rest of program using whitespace

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Symbolic Constants A symbolic constant is defined in a

declaration statement using the modifier const.

A symbolic constant allocates memory for an object that can not be modified during program execution Attempt to modify constant syntax error

A symbolic constant must be initialized in the declaration statement

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Assignment Operator The assignment operator (=) is used in C++

to assign a value to a memory location. The assignment statement:x1 = 1.0; assigns the value 1.0 to the variable x1. Thus, the value 1.0 is stored in the memory

location associated with the identifier x1.

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Example 1 - initializationdouble sum = 0; sum

Example 2int x;x=5; x

Assignment Operators - Examples

0

5

a

Example 3char ch;ch = 'a'; ch

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Assignment Statements - continued

Example 4int x, y, z;x=y=0;z=2; x

y

z

How is the memory map affected by the following statement?y = z;

0

0

2

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Arithmetic Operators Addition + Subtraction - Multiplication * Division / Modulus %

Modulus returns remainder of division between two integers

Example5%2 returns a value of 1

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Integer Division Division between two integers results in an

integer. The result is truncated, not rounded Example:

The expression 5/3 evaluates to 1

The expression 3/6 evaluates to 0

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Priority of Operators1. Parentheses Inner most first

2. Unary operatorsRight to left (+ -)

3. Binary operators Left to right (* / %)

4. Binary operators Left to right (+ -)

Increment/decrement operators Increment Operator ++

post increment x++; pre increment ++x;

Decrement Operator - - post decrement x- -; pre decrement - -x;

For examples assume k=5 prior to executing the statement.

m= ++k; both m and k become 6 n = k- -; n becomes 5 and k becomes 4

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Abbreviated Assignment Operatorsoperator example equivalent statement += x+=2; x=x+2;

-= x-=2; x=x-2;

*= x*=y; x=x*y;

/= x/=y; x=x/y;

%= x%=y; x=x%y;

04/20/23Engineering Problem Solving with C++,

Etter,Ingber Second Edition 28

Precedence of Arithmetic and Assignment Operators

Precedence Operator Associativity 1 Parentheses: () Innermost first

2 Unary operators

+ - ++ -- (type)

Right to left

3 Binary operators * / %

Left ot right

4 Binary operators + -

Left ot right

5 Assignment operators = += -= *= /= %=

Right to left

Input/output streams C++ has three standard input/output streams

cin is the standard input (e.g., keyboard) cout is the standard output cerr is the standard error

Standard input Use the stream input operator >> to direct

keyboard input to variables

General Form: cin >> identifier >> identifier;

Input value must be compatible with identifier type

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Input/output streams (cont.) Standard output

Use the stream output operator << to direct data to cout

General Form:cout << expression << expression;

Note: An expression is a C++ constant, identifier, formula, or function call.

endl can be used to place an output character in the buffer and flush the buffer

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04/20/23Engineering Problem Solving with C++,

Etter,Ingber Second Edition 31

output1,24.5 cm_

//Example1: Determine the output#include <iostream>#include <string>using namespace std;int main(){

int i, j;double x;string units = " cm";cin >> i >> j;cin >> x;cout << "output \n";cout << i << ',' << j << endl << x << units << endl;return 0;

} //Input stream:1 2 4.5

04/20/23Engineering Problem Solving with C++,

Etter,Ingber Second Edition 32

//Example 2: Determine the output#include <iostream>using namespace std;int main(){

int i, j;double x, y;cin >> i >> j >> x >> y;cout << "First output " << endl;cout << i << ',' << j << ',' << x << ',' << y << endl;cin >> x >> y >> i >> j;cout << "Second output" << endl;cout << i << ',' << j << ',' << x << ',' << y << endl;return 0;

} //Input stream is:1 23.4 52 3 3.4 7

First output1,2,3.4,5Second output3,2,2,3_

04/20/23Engineering Problem Solving with C++,

Etter,Ingber Second Edition 33

Characters and input

>> discards leading whitespace get() method used to input whitespace characters Example:

int x;char ch;cin >> x >> ch;cin >> x;

cin.get(ch); x ch

x chInput stream:45 c39b

45 ‘c’

39 ‘\n ’

Final notes Next time

Functions in C++--pass by value, reference Potentially cover pointers as well

Acknowledgements: this lecture borrows heavily from lecture slides provided with the following texts: Etter & Ingber, Engineering Problem Solving with

C++, 2nd ed. Deitel & Deitel, C++ How to Program, 6th ed.

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