Programming for Programming for BeginnersBeginners

Martin Nelson

Elizabeth FitzGerald

Lecture 13: An Introduction to C++

Session 13 – aims and objectives

So far we’ve only talked about Java, but there are many other languages available...

Today, we will take a quick look at one alternative: C++.

We will see that C++ has many similarities to Java.

There are also many key differences.

Languages Available So far, we’ve only talked about Java, but there are

many other languages available...

Language choice depends on the task in hand!

Procedural Fortran COBOL (old versions) Pascal C Perl

Object-oriented COBOL (latest version) C++ C# Java Delphi Visual Basic Perl

Languages Available Fortran (acronym for formula translator) is one of the

oldest high-level languages. It is still commonly used for mathematical/scientific computation.

COBOL (Common business-oriented language) is another old high-level language. Some argue that it is now very out-dated. Was used for business applications running on large computers. Required very wordy coding!

Pascal – often used for teaching, but not much else. Very inflexible.

Perl (Practical Extraction & Report Language) is a programming language especially designed for processing text. Good for quick program development, task automation and some web applications.

C Procedural language Originally designed as a systems programming

language – e.g. Unix. Can be used for a variety of applications, from

business programs to engineering. Requires less memory than other languages. Lower-level, a lot closer to assembly language

than other high-level languages this can make it unsuitable for some applications –

especially those requiring rapid development.

C++

C, but incremented once! Includes object-orientation, but can still use

procedural syntax too. Popular for writing programs for graphical

applications, such as Windows or Mac applications Good general language to learn, especially if you

want a job as a programmer!

C# Hybrid of C and C++, written by Microsoft to

compete with Java. Object-oriented programming language used with

XML-based web services on the .NET platform. We’ll talk about XML next time... The .NET framework allows interaction between codes

written in different languages.

Designed for improving productivity in the development of web applications.

Many similarities to Java!

Differences between C and C++

C++ is object-oriented; C is not

C++ standardizes how objects are created and managed; C is a lot more variable in terms of style and design.

C++ applications are slower at runtime and slower to compile than C programs.

C++ programs tend to be larger than C.

C interacts with memory much more than C++ (pointers).

Compiling C++ Code on Granby Various C++ compilers are available. We will use g++

C++ files are usually given the extension .cpp

To compile the file test.cpp:

g++ test.cpp

By default, the compiler will create an executable called a.out. To run it, type

./a.out

Or, we can give the output a specific name (test):

g++ -o test test.cpp

./test

Compiling C++ Code on Granby Various C++ compilers are available. We will use g++

C++ files are usually given the extension .cpp

To compile the file test.cpp:

g++ test.cpp

By default, the compiler will create an executable called a.out. To run it, type

./a.out

Or, we can give the output a specific name (test):

g++ -o test test.cpp

./test

Input file name

Output file name

Hello World

Typical beginner’s program Used as first exposure to a new programming

language or environment Can be written in loads of different languages:

http://www2.latech.edu/~acm/HelloWorld.html

(lists 204 examples of different Hello World programs!)

Hello World in Java

class Hello{ public static void main (String[] args); {

System.out.print("Hello World"); }

}

Hello World in C

#include <stdio.h>

main() { printf ("Hello World!\n"); }

Just as in Java, every C program has a method called main, which is run when the program starts.

The printf method is used to write some text on the screen.

Header file providingthe printf method

Hello World in C++

#include <iostream>

using namespace std;

int main() { cout << “Hello World!\n"; return 0; } In C++, cout represents the standard output

stream (the screen. The operator << can be read as “send to”.

Provides cout

Don’t worry aboutthis yet!

In C++, main must return an int.

User Input in C++

Just as cout is the standard output stream (the screen), we have cin to represent the standard input (the keyboard).

The operator >> means “read from”.

User Input in C++#include <iostream>

#include <string>

using namespace std;

int main()

{

string name;

cout <<“Tell me your name!” << endl;

cin >> name;

cout << “Hello “ << name << endl;

return 0;

}

Provides cout & cin

Provides the string class

Declare a string

Newline

Flow Control in C++ For loop:

for( int i=1; i<100; i++)

{

cout << i << endl;

}

While loop:

int i=100;

while(i>0)

{

cout << i << endl;

i--;

}

Flow Control in C++ If statement:

int score;

cout << “Enter your exam mark” << endl;

cin >> score;

if(score<40)

{

cout << “You failed!” << endl;

}

else

{

cout << “You passed!” << endl;

}

Arrays in C++double nums[3];

nums[0] = 1;

nums[1] = 12;

nums[2] = 428;

double total = nums[0]+nums[1]+nums[2];

cout << “Total is “ << total << endl;

Beware: C++ will let you refer to nums[3] in the above, but that data will rarely make sense and is likely to make your code malfunction.

Can also have arrays of arrays! e.g. nums[4][5]

Declare an array

Assign values

Methods in C++

Easiest way (for now) is to define methods above main.

Can also define methods below main, or in separate files, but this is harder. We’ll ignore these options for now.

Just like Java, methods have a return type and (optionally) a list of arguments.

Methods in C++#include <iostream>

using namespace std;

// Method to add two numbers together

double add(double a, double b)

{

return a+b;

}

int main()

{

cout << add(1,3) << endl;

return 0;

}

Want to know more about C++?if(answer==no)

{

Stop listening for a minute!

}

else

{

Sign up for the forthcoming C++ course!

}

C++ Programming

Ten Sessions: 12th April – 17th May 2011

Tutor: Dr. Robert Oates (rxo@cs.nott.ac.uk)

More info: www.nottingham.ac.uk/csc

Exercises

Choice of exercises for today:

Either have a go at some new exercises, which introduce some familiar concepts in C++.

Or, continue with your Java Address Book.

Coming up in Session 14

An introduction to scripting languages HTML

CSS

XML/XSLT

php

javascript