Programming for Beginners

2. First Programs

Taste of Things to Come: Iteration

The last program of this introductory chapter will show you how to do repetitions in C++. As we have already discussed, statements in a program are executed in sequence. However, there are special statements that can change the order of execution. One such statement is the iteration statement.

The main iteration statement in C++ is called for. At first sight, the for statement may appear slightly intimidating since it is a bit more complicated to write than the statements we have seen thus far. Nevertheless, let us take a look at it:

Note that the for statement is not ended by a semicolon symbol.

int main()
{
    cout << "I sing" << endl;
    for (double i=1;i<=3;i++)
        {
        cout << "Sail sail" << endl;
        cout << "my little boat" << endl;
        }  
    cout << "While I catch my fish" << endl;  
} 

As you can see, the word for is followed by a pair of parentheses (i.e. round brackets) enclosing a rather arcane looking piece of code. For the time being, we will leave the magic of this incantation undisturbed and bring your attention only to the number 3 that signifies how many repetitions there are. This for statement thus demands that three iterations (i.e. repetitions) be performed.

A sequence of statements inside a pair of braces (i.e. curly brackets) is called a statement block. A for statement controls the statement block by repeating it as many times as has been specified. This statement block will be repeated (i.e. iterated) three times. In each iteration, the statements in a statement block will be executed in the usual order, one by one.

This is what the program outputs:

STDOUT:

I sing
Sail sail 
my little boat
Sail sail 
my little boat
Sail sail 
my little boat
While I catch my fish