C Language | Flow Control | for Statement

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The for statement places loop initialization, a condition, and an update expression in one construct.

Counter-Controlled Loops

The syntax is:

for (initialization; condition; update) statement

It corresponds to:

initialization;
while (condition) {
  statement;
  update;
}

All three expressions may be omitted. With no condition, the loop is infinite: for (;;) { ... }.

#include <stdio.h>

int main(void) {
  int iMax, iCount;
  printf("Enter the number of repetitions. >");
  for (scanf("%d", &iMax), iCount = 0; iCount < iMax; iCount++)
    printf("iteration %d\n", iCount);
  return 0;
}

The comma between arguments in scanf() is a separator. The comma between scanf(...) and iCount = 0 is the comma operator, which evaluates expressions from left to right. It can be useful in a for expression, but excessive use reduces readability.

Loops can be nested.

for (iOp1 = 1; iOp1 < 10; iOp1++) {
  for (iOp2 = 1; iOp2 < 10; iOp2++)
    printf("%2d ", iOp1 * iOp2);
  printf("\n");
}

This prints a multiplication table.