Using while 


/*factorial.c - Copyright (c) 1998 Matthew Belmonte.*/

#include <stdio.h>

int main(void)
  {
  int n;
  long factorial;
  printf("Compute the factorial of what number? ");
  scanf("%d", &n);
  factorial = 1L;
  while(n > 0)
    {
    factorial *= n--;
    }
  printf("The factorial is %ld\n", factorial);
  return 0;
  }
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