For Loops

The for statement is a looping structure designed specifically to simplify the implementation of count-controlled loops (That is, a count-controlled while loop can be replaced by a for loop.). The loop-control variable, the beginning value, the ending value, and the incrementation are explicitly part of the for loop heading itself.

The syntax template for a for statement is

   
for (Init_Statement; Boolean_Expression; Update_Expression)
{
   // Statements
}
   

Each part inside the () parentheses of the for loop can be any line of code, but usually they are used like this:

• The Init_Statement usually initializes a loop control variable. It can also declare the variable. If it does, the variable's scope ends with the loop.
• The Boolean_Expression is equivalent to a while condition.
• The Update_Expression usually increments or decrements the loop control variable.

The following for loop reads 10 marks and sums them up.

 
int  sum = 0;
for (int counter = 1; counter <= 10; counter++)
{
       	cout << "Please enter a mark: ";
	cin >> mark;
	sum = sum + mark;
}

The following for loop also reads 10 marks and sums them up.

 
int  sum = 0;
for (int counter = 10; counter > 0; counter--)
{
       	cout << "Please enter a mark: ";
	cin >> mark;
	sum = sum + mark;
}

Of course, all for loops can be written as count-controlled while loops. For example, we can change the previous program segment to the following equivalent piece of code.

 
int  sum = 0;
int counter = 1; 
while(counter <= 10)
{
       	cout << "Please enter a mark: ";
	cin >> mark;
	sum = sum + mark;
	counter++;
}