C语言for循环实例省略表达式

/* for_none.c */
#include <stdio.h>
int main(void)
{
    int ans, n;

    ans = 2;
    for (n = 3; ans <= 25; )
        ans = ans * n;
    printf("n = %d; ans = %d.\n", n, ans);
    return 0;
}