C++ Programming Basics

Programming on Unix

Getting started with UNIX

• Multiuser system

– Each user gets a slice of the CPU’s time

– You must log on to tell the OS you are a legal user

– The CS department’s computer’s name is esus.

• Security

– Since each user has their own disk space, it is necessary to protect files from open access

– Permissions allow you to protect your files from other esus users.

Linux

• Linux is a free version of UNIX distributed by GNU (The Free Software Foundation).

• The source code was released, encouraging hundreds of programmers to add to it and make changes.

• The computers in 254 EPS dual boot; they can run either the Windows OS or Linux

• Be sure your machine is booted with Linux.

Before you start

• You must have an esus account

– Login name and password

– These are set up automatically for all CS students

• Changing your password

– passwd changes the password

• erase key (either backspace or delete)

• interrupt key (control-C)

• Remember, UXIX is case sensitive

Writing your programs on Linux

• First must decide on a text editor

– I will show you pico; other choices are emacs and vi

• After the program is written, it must be compiled

– We will use the g++ compiler in lab

– On your own computer, you may use any C++ compiler you want, but the source code must port to lab and the g++ compiler

– If you keep your code standard, there should not be too much problem with porting the code.

A Simple C++ Program

#include <iostream>
using namespace std;
int main( )
{
cout <<“First program for CS 210”<<endl;
return 0;
}

Note this about the program

• Functions

– The main( ) function is not inside a class like a Java program

• Functions are one of the fundamental building blocks of C++ (not always classes)

– Like Java,

• parentheses follow the function name

• the function has a return type

• the body of the function is surrounded by braces

• execution of the program will begin with main( )

• Whitespace is not important to the compiler

• Terminal output is done using the cout object and the << (the insertion operator)

• Similarly, terminal input uses cin and the >> (extraction operator)

• The preprocessor

– Both #include <iostream> and using namespace std; are directives to the compiler

– An #include directive substitutes an entire file for the #include line

Primitive types in C++

• Integer types

– short, int, long

• How many bits for each is implementation dependant

– Each can be modified by signed or unsigned

• They are signed by default

• Floating point types

– float, double

• Character type char

• Boolean type called bool in C++

Character and string constants

• Character constants are enclosed in single quotes

– Example char middleInitial = ‘M’;

• String constants are enclosed in double quotes

– Example string st = “this is a string”;

– To use strings, include the <string> header

Branching and loops

• If/else statement is identical to Java except:

– In C++ an integer is also a boolean; zero is false an any other integer is true

– The switch statement is also the same

• Loops are the same as in java

– Possibilities: for loop, while loop, and do loop

– I advise against using break and continue

Assigning values to variables

• The Java compiler will not let you fail to give variables an initial value

• The C++ compiler will not give an error message if a variable is not initialized

– This can lead to errors, since there is always something in every byte of RAM

– Many C++ compilers will give a warning

Simple Input/Output in C++

• Use cout << to send data to the screen

– A linefeed can be sent in two ways

• \n within a string: “type this\n second line”

• endl outside a string: cout << “string” <<endl;

• Use cin >> to read from the keyboard

– Use: cin >> variable_name;

• Both >> and << can be cascaded

– You can use more than one insertion or extraction operator in a statement

Manipulators

• Manipulators are used with the insertion operator << to modify the way output is displayed.

– endl is a manipulator

– The setw(n) manipulator

• This makes the field n characters wide

• You must include the iomanip header file to use setw(n)

– #include <iomanip>

• There is a table of the manipulators on page 572 of the Lafore book

Escape Sequences

• Escape sequences can also be used to format output.

An example is the \n

• Escape sequences always start with a backslash

• They can be used either as separate characters or embedded in a string constant

• There is a table of common escape sequences on page 44 of Lafore.