The syntax is
for (expr1; expr2; expr3) statementAny or all of the three expressions can be omitted, but the semi-colons must remain. If expr2 is not present, it is assumed to be true.
What happens in general is as follows:
expr1;
while (expr2)
{
statement
expr3;
}
and so expr2 must initially be true for the statement to be executed.
In practice, the commonest use has expr1 initializing a loop counter; expr2 checking if the loop has finised; expr3 updating the loop counter, as follows.
Example
int x, total; total= 0; /* Loop ten times */ for (x= 1; x<=10; x= x + 1) total= total + x;