for statement in C++

The for statement or for loop is useful while executing a statement multiple number of times.

The for loop is the most commonly used statement in C++. This loop consists of three expression:

• The first expression is used to initialize the index value
• The second expression is used to check whether or not the loop is to be continued again
• The third expression is used to change the index value for further iteration

The general form of for statement is:

for(expression 1; expression 2; expression 3)
statement;

In other words,

for(initial condition; test condition; incrementer or decrementer)
{
statement1;
statement2;
.....
.....
}

Where,

• expression 1 is the initialization of the expression or the condition called an index
• expression 2 is the condition checked. As long as the given expression is true the loop statement will be repeated
• expression 3 is the incrementer or decrementer to change the index value of the for loop variable

Typically, expression 1 is an assignment expression, expression 2 is a logical expression and expression 3 is a unary expression or an assignment expression.

When the for statement is executed, expression 2 is evaluated and tested at the begening of each pass through the loop and expression 3 is evaluated at the end of each pass.

Program to compute a sum of consecutive integers, i.e., the program to compute the sum 1 + 2 + 3 + .. + n, for an integer input n.

#include
{
int n;
cout << "Enter a positive integer: "; cin >> n;
long sum = 0;

for(int i=1; i<=n; i++)
{
sum = sum + i;
}

cout << "Sum of first " << n << " integers is " << sum;
}