Programming for Beginners Lecture 13: An Introduction to C++ Martin Nelson Elizabeth FitzGerald
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! Object-oriented • COBOL (latest version) • C++ • C# • Java • Delphi • Visual Basic • Perl Procedural • Fortran • COBOL (old versions) • Pascal • C • 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 providing the 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 about this 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++ Provides cout & cin #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 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
