可变参数模拟实现printf

#include<stdio.h>
#include<stdarg.h>
#include<assert.h>
void myprintf(const char *s1, ...)
{
  assert(s1 != NULL);
  va_list arg;
  char c;
  char ch;
  char *str;
  int temp;
  va_start(arg, s1);
  while (c=*s1++)
  {
    switch (c)
    {
    case'%' :
      break;
    case 'c':
      ch = va_arg(arg,int);
      putchar(ch);
      break;
    case 's':
      str = va_arg(arg, char *);
      fputs(str, stdout);
      break;
    case 'd':
      temp = va_arg(arg, int);
      printf("%d",temp);
      break;
    default:
      putchar(c);
    }  
  }
  va_end(arg);
}
int main()
{
  char *s = "aaaaaa";
  char c = 'b';
  int i = 1997;
  myprintf("%s\n %c \n%d", s, c, i);
  system("pause");
}