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Lecture 2: First Program1

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Topics of this lecture

Introduce first program Explore inputs and outputs of a program

Arithmetic using C++ Introduce the conditional statement

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General Notes About C++and This Book Book geared toward novice programmers

Stress programming clarity C and C++ are portable languages

Portability C and C++ programs can run on many different

computers Compatibility

Many features of current versions of C++ not compatible with older implementations

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Introduction to C++ Programming C++ language

Facilitates structured and disciplined approach to computer program design

Following several examples Illustrate many important features of C++ Each analyzed one statement at a time

Structured programming Object-oriented programming

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A Simple Program:Printing a Line of Text Comments

Document programs Improve program readability Ignored by compiler Single-line comment

Begin with //

Preprocessor directives Processed by preprocessor before compiling Begin with #

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Basics of a Typical C++ Environment Input/output

cin Standard input stream Normally keyboard

cout Standard output stream Normally computer screen

cerr Standard error stream Display error messages

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fig01_02.cpp(1 of 1)

fig01_02.cppoutput (1 of 1)

1 // Fig. 1.2: fig01_02.cpp

2 // A first program in C++.

3 #include <iostream>

4 5 // function main begins program execution

6 int main()

7 {8 std::cout << "Welcome to C++!\n";

9 10 return 0; // indicate that program ended successfully

11 12 } // end function main

Welcome to C++!

Single-line comments.

Preprocessor directive to include input/output stream header file <iostream>.

Function main appears exactly once in every C++ program.

Function main returns an integer value.Left brace { begins function body.

Corresponding right brace } ends function body.

Statements end with a semicolon ;.

Name cout belongs to namespace std.

Stream insertion operator.

Keyword return is one of several means to exit function; value 0 indicates program terminated successfully.

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A Simple Program:Printing a Line of Text Standard output stream object

std::cout “Connected” to screen <<

Stream insertion operator Value to right (right operand) inserted into output stream

Namespace std:: specifies using name that belongs to “namespace” std

std:: removed through use of using statements Escape characters

\ Indicates “special” character output

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A Simple Program:Printing a Line of Text

Escape Sequence Description

\n Newline. Position the screen cursor to the beginning of the next line.

\t Horizontal tab. Move the screen cursor to the next tab stop.

\r Carriage return. Position the screen cursor to the beginning of the current line; do not advance to the next line.

\a Alert. Sound the system bell.

\\ Backslash. Used to print a backslash character.

\" Double quote. Used to print a double quote character.

Make some modifications to First Program

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Another Simple Program:Adding Two Integers Variables

Location in memory where value can be stored Common data types

int - integer numbers char - characters double - floating point numbers

Declare variables with name and data type before useint integer1;

int integer2;

int sum; Can declare several variables of same type in one declaration

Comma-separated list

int integer1, integer2, sum;

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Another Simple Program:Adding Two Integers Variables

Variable names Valid identifier

Series of characters (letters, digits, underscores) Cannot begin with digit Case sensitive

Naming Conventions start with a lower case letter mix of lower and uppercase letters and numbers short but meaningful generally avoid single letter variables

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Another Simple Program:Adding Two Integers Input stream object

>> (stream extraction operator) Used with std::cin Waits for user to input value, then press Enter (Return) key Stores value in variable to right of operator

Converts value to variable data type

= (assignment operator) Assigns value to variable Binary operator (two operands) Example:

sum = variable1 + variable2;

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1 // Fig. 1.6: fig01_06.cpp

2 // Addition program.

3 #include <iostream> 4 // function main begins program execution

5 int main() {6 int integer1; // first number to be input by user

7 int integer2; // second number to be input by user

8 int sum; // variable in which sum will be stored

9 10 std::cout << "Enter first integer\n"; // prompt

11 std::cin >> integer1; // read an integer

12 13 std::cout << "Enter second integer\n"; // prompt

14 std::cin >> integer2; // read an integer

15 16 sum = integer1 + integer2; // assign result to sum 17 std::cout << "Sum is " << sum << std::endl; // print sum

18 19 return 0; // indicate that program ended successfully 20 } // end function main

Declare integer variables.

Use stream extraction operator with standard input stream to obtain user input.

Stream manipulator std::endl outputs a newline, then “flushes output buffer.”

Concatenating, chaining or cascading stream insertion operations.

Calculations can be performed in output statements: alternative for lines 16 and 17:

std::cout << "Sum is " << integer1 + integer2 << std::endl;

fig01_06.cpp(1 of 1)

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Microsoft Visual C++ numeric data types

Type Name Bytes Other Names Range of Values

int * signed, signed int System dependent

unsigned int * unsigned System dependent

__int8 1 char, signed char –128 to 127

__int16 2 short, short int, signed short int

–32,768 to 32,767

__int32 4 signed, signed int –2,147,483,648 to 2,147,483,647

__int64 8 none –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

char 1 signed char –128 to 127

unsigned char 1 none 0 to 255

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Type Name Bytes Other Names Range of Values

short 2 short int, signed short int

–32,768 to 32,767

unsigned short 2 unsigned short int 0 to 65,535

long 4 long int, signed long int

–2,147,483,648 to 2,147,483,647

unsigned long 4 unsigned long int 0 to 4,294,967,295

enum * none Same as int

float 4 none 3.4E +/- 38 (7 digits)

double 8 none 1.7E +/- 308 (15 digits)

long double 10 none 1.2E +/- 4932 (19 digits)

Microsoft Visual C++ numeric data types

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Memory Concepts

Variable names Correspond to actual locations in computer's

memory Every variable has name, type, size and value When new value placed into variable, overwrites

previous value Reading variables from memory nondestructive

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Memory Concepts

std::cin >> integer1; Assume user entered 45

std::cin >> integer2; Assume user entered 72

sum = integer1 + integer2;

integer1 45

integer1 45

integer2 72

integer1 45

integer2 72

sum 117

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Effect of Several Assignments What are the values of a and b after all

statements are executed?int a = 1;int b;b = a;a = 2;

a = 2, b = 1

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Arithmetic

Arithmetic calculations *

Multiplication /

Division Integer division truncates remainder

7 / 5 evaluates to 1

% Modulus operator returns remainder

7 % 5 evaluates to 2

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Arithmetic Rules of operator precedence

Operators in parentheses evaluated first Nested/embedded parentheses

Operators in innermost pair first

Multiplication, division, modulus applied next Operators applied from left to right

Addition, subtraction applied last Operators applied from left to right

Operator(s) Operation(s) Order of evaluation (precedence)

() Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.

*, /, or % Multiplication Division Modulus

Evaluated second. If there are several, they re evaluated left to right.

+ or - Addition Subtraction

Evaluated last. If there are several, they are evaluated left to right.

X = 7 + 4 / 2 * (3 * ( 4 – 3) + 5) % 2 + 3

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Decision Making: Equality and Relational Operators if structure

Make decision based on truth or falsity of condition If condition met, body executed Else, body not executed

Equality and relational operators Lower precedence than arithmetic operators Equality operators

Same level of precedence Relational operators

Same level of precedence Associate left to right

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Decision Making: Equality and Relational Operators

Standard algebraic equality operator or relational operator

C++ equality or relational operator

Example of C++ condition

Meaning of C++ condition

Relational operators

> > x > y x is greater than y

< < x < y x is less than y

>= x >= y x is greater than or equal to y

<= x <= y x is less than or equal to y

Equality operators

= == x == y x is equal to y

!= x != y x is not equal to y

Notice:

“==“

(not “=“)

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using statements

Eliminate the need to use the std:: prefix Allow us to write cout instead of std::cout To use the following functions without the std:: prefix, write the following at the top of the program

using std::cout; using std::cin; using std::endl;

Look at example program