Answer SL19

This looks like a scoping problem. (Experienced programmers develop an instinct for such things.)

#include <stdio.h>

int j;

int fact( int n)
{
  int value = 1;
  for ( j=1; j<=n; j++ ) value *= j;
  return value;
}

int main ( void )
{
  for ( j=1; j<7; j++ )
    printf("factorial of %d is %d\n", j, fact(j) );

  return 0 ;
}

Comments: The global variable j is used as a loop control variable in two loops that are sometimes both active. This can only lead to problems.

The first time main's loop executes, j is set to 1. But then, just before fact's loop exits, the same j is set to 2. So the program writes out:

factorial of 2 is 1

The problem can be fixed by declaring a local variable for each loop. The problem in this example is obvious (I hope). But this is a frequent mistake in student programs. In a longer program, this problem is harder to find.