#include <stdio.h>

#include <string.h>

#include <stdlib.h>

long factorial(int n)

{

  if(n == 1)

    return 1;

  else

    return n*factorial(n-1);

}

int main(int argc,char *argv[])

{

  int n = 0;

  if(argc != 2)

  {

    printf("input error,exit!!\n");

    return -1;

  }

  n = atoi(argv[1]);

  printf("%d! = %ld\n",n,factorial(n));

  return 0;

}

  #include <stdio.h> 
  #include <stdlib.h> 
  #include <string.h> 
    
  #define MAX 3000 
    
  //存儲(chǔ)每次階乘運(yùn)算的結(jié)果 
  int str[MAX]; 
    
  void calculateFactorial(int n); 
    
  int main() 
  { 
    int n; 
    
    while (scanf("%d", &n) != EOF) { 
      if(n == 0) { 
        printf("1\n"); 
      } else { 
        calculateFactorial(n); 
      } 
    } 
    
    return 0; 
  } 
    
  void calculateFactorial(int n) 
  { 
    int i, j, temp, c, len; 
    
    memset(str, 0, sizeof(str)); 
    str[1] = 1; 
    
    for (i = 2, len = 1; i <= n; i ++) { //循環(huán)與2,3,..n相乘 
      for (j = 1, c = 0; j <= len; j ++) { //str數(shù)組代表一個(gè)數(shù)，模擬與i相乘 
        temp = str[j] * i + c; 
        str[j] = temp % 10; 
        c = temp / 10; 
      } 
      while(c > 0) 
      { 
        str[j ++] = c % 10; 
        c /= 10; 
      } 
      len = j - 1; 
    } 
    
    for (i = len; i >= 1; i --) { 
      printf("%d", str[i]); 
    } 
    printf("\n"); 
  }