The for statement

A for statement provides the following benefits:

Evaluate an expression before the first iteration of the statement (initialization)
Specify an expression to determine whether or not the statement should be processed (the condition)
Evaluate an expression after each iteration of the statement (often used to increment for each iteration)
Repeatedly process the statement if the controlling part does not evaluate to false (or 0 in C).

for statement syntax

expression1 is the initialization expression. It is evaluated only before the statement is processed for the first time. You can use this expression to initialize a variable. You can also use this expression to declare a variable, provided that the variable is not declared as static (it must be automatic and may also be declared as register). If you declare a variable in this expression, or anywhere else in statement, that variable goes out of scope at the end of the for loop. If you do not want to evaluate an expression prior to the first iteration of the statement, you can omit this expression.

expression2 is the conditional expression. It is evaluated before each iteration of the statement. C only begins expression2 must be of arithmetic or pointer type. C only ends C++ only begins expression2 must be convertible to type bool. C++ only ends

If expression2 evaluates to C only begins 0 C only ends or C++ only begins false C++ only ends , the statement is not processed and control moves to the next statement following the for statement. If expression2 does not evaluate to false, the statement is processed. If you omit expression2, it is as if the expression had been replaced by true, and the for statement is not terminated by failure of this condition.

expression3 is evaluated after each iteration of the statement. This expression is often used for incrementing, decrementing, or assigning to a variable. This expression is optional.

A break, return, or goto statement can cause a for statement to end, even when the second expression does not evaluate to false. If you omit expression2, you must use a break, return, or goto statement to end the for statement.

Examples of for statements

The following for statement prints the value of count 20 times. The for statement initially sets the value of count to 1. After each iteration of the statement, count is incremented.

int count;
for (count = 1; count <= 20; count++)
   printf("count = %d\n", count);

The following sequence of statements accomplishes the same task. Note the use of the while statement instead of the for statement.

int count = 1;
while (count <= 20)
{
   printf("count = %d\n", count);
   count++;
}

The following for statement does not contain an initialization expression:

for (; index > 10; --index)
{
   list[index] = var1 + var2;
   printf("list[%d] = %d\n", index,
   list[index]);
}

The following for statement will continue running until scanf receives the letter e:

for (;;)
{
   scanf("%c", &letter);
   if (letter == '\n')
      continue;
   if (letter == 'e')
      break;
   printf("You entered the letter %c\n", letter);
}

The following for statement contains multiple initializations and increments. The comma operator makes this construction possible. The first comma in the for expression is a punctuator for a declaration. It declares and initializes two integers, i and j. The second comma, a comma operator, allows both i and j to be incremented at each step through the loop.

for (int i = 0,
j = 50; i < 10; ++i, j += 50)
{
   cout << "i = " << i << "and j = " << j
   << endl;
}

The following example shows a nested for statement. It prints the values of an array having the dimensions [5][3].

for (row = 0; row < 5; row++)
   for (column = 0; column < 3; column++)
      printf("%d\n",
      table[row][column]);

The outer statement is processed as long as the value of row is less than 5. Each time the outer for statement is executed, the inner for statement sets the initial value of column to zero and the statement of the inner for statement is executed 3 times. The inner statement is executed as long as the value of column is less than 3.