Lecture 3 -- 1Computer Science I - Martin Hardwick

The Programming Process

Use an editor to create a program file (source file).

contains the text of the program

Use a compiler to convert the source file into a machine code file (object file).

convert from “English” to binary with machine operations

Use a linker to convert the object file into an executable file.

include other machine code that the program requires

In Visual C++ make sure you create an “empty” project or you will get linker errors

Run the executable file.

Iterate from any point as needed.

Editor

Program.cpp

Compiler

Program.objLibraries

Linker

Program.exe

Run theProgram

Done

success

errors

errors

errors

Lecture 3 -- 2Computer Science I - Martin Hardwick

The First C++ Program

// Hello World Program// Author: Martin Hardwick

#include <iostream>using namespace std;

int main (){

cout << “Hello World!” << endl;

return 0;

}

Anything following // is a comment intended to improve the readability of the program.

#include is used to tell the compiler and linker what library resources the program uses.

the <iostream> resource defines everything you need to display messages on the screen

The line “using namespace std;” says you want to use standard c++ names for things

This program contains one function named “main”.

Lecture 3 -- 3Computer Science I - Martin Hardwick

Defining A C++ Function

A C++ function has the following form:

The name of this function is “main”.

The word “int”, means that this functions returns an integer number. usually 0 to indicate that the program ran correctly. this is what the return statement does at the end of the

function

The braces define the beginning and the end of the function.

The first line of the function is called the function header.

int main ( ){ sequence of statements separated by semicolons . . . return 0;}

Lecture 3 -- 4Computer Science I - Martin Hardwick

Displaying Messages On The Screen

To display a message on the computer screen use the cout statement.

The << operator says to display whatever immediately follows it. the << operator applies only to the first thing following it to display two things, use the << operator twice, once

immediately before each

The word “endl” means to start a new line.

Text strings must always be surrounded by double quotes.

More examples:

cout << “This is a message to display” << endl;

cout << “Hello World!” << endl;

cout << “First part of long message” << “Second part of long message” << endl;

Lecture 3 -- 5Computer Science I - Martin Hardwick

C++ Variables

A computer does not remember numbers from one statement in your program to the next.

you must save any number that you will need later in a word of memory (called a variable in C++)

Each variable that a C++ program uses must be declared. specify a name for the variable specify the type of the variable

– valid types include: int -- one word integerdouble -- two

word floating-point (real)

The variable declarations in a C++ function are usually placed at the beginning of that function by convention.

Examplesdouble radius;int quantity;

Lecture 3 -- 6Computer Science I - Martin Hardwick

Assignment Statement

An assignment statement is used to put a value into a variable. The previous value is replaced

Syntax: <variable> = <expression>;

<variable> is any declared variable in the program <expression> is anything that produces a value of

the appropriate type (more on this later) the number produced by the <expression> is

assigned as the new value for the variable

Examples:

size = 10;width = length - 2;count = count + 1;

Lecture 3 -- 7Computer Science I - Martin Hardwick

The cin Object

Used to assign a value typed on the keyboard to a variable.

The >> operator says to assign the next value typed on the keyboard to the variable appearing immediately after the >> operator.

The user must type a value followed by the Enter Key.

An integer number is converted to a real number for assignment to a double variable.

cin >> x;cin >> y;cin >> z;

equivalent to: cin >> x >> y >> z;

If x, y and z are double variables and the user types:

10.2 -5.2 6

x is assigned 10.2y is assigned -5.2z is assigned 6.0

The user can also type:

10.2-5.2 6

Lecture 3 -- 8Computer Science I - Martin Hardwick

Names In C++

Variable names in C++ are called identifiers.

identifiers are used for many other things as well

Rules for constructing valid identifiers in C++:

can contain letters (upper and lower case), digits, and the underscore ( _ ) character

cannot start with a digit cannot be a reserved word can be at most 256

characters long are case sensitive Must not already be used

Reserved words in C++:

asm auto bool break case catch char class const const_cast continue default delete do double dynamic_cast delete else enum explicit extern false

floatfor friend goto if inline int long mutable namespace new operator private protected public register reinterpret_cast returnshortsigned sizeof

staticstatic_cast switchtemplate this throw true try typedeftypeidtypenameunionunsignedusingvirtualvoidvolatilewchar_twhileunionunsigned

Lecture 3 -- 9Computer Science I - Martin Hardwick

Putting it all together

Lets write a program to convert dollars to euros Find out current exchange rate Get amount in dollars Apply formula to convert from dollars to euros Display amount in euros

int main () {

}

Quiz 1 Monday after Labor Day (September 14)