23 时间：24小时制转12小时制

#include <stdio.h>   //错误，答案；范围错了，比如输入12:00只会得到12:00am但是需要的是pm
main()
{
    int shi,fen;
    scanf("%d:%d",&shi,&fen);
    if(shi>12)
        printf("%02d:%02d p.m.",shi-12,fen);
    else
        printf("%02d:%02d a.m.",shi,fen);
    return 0;

}

#include <stdio.h>
#include <stdlib.h>
  
int main()
{
    int xs,fz,swxw=1;
    scanf("%d:%d",&xs,&fz);
    if(xs == 0)
        {xs = 12;swxw = 1;}
    else if(xs > 12)
        {xs -= 12;swxw = 0;}
    else if(xs < 12)
        swxw = 1;
    else if(xs == 12)
        swxw = 0;
  
    if(xs < 10)
        printf("0%d:",xs);
    else
        printf("%d:",xs);
    if(fz < 10)
        printf("0%d ",fz);
    else
        printf("%d ",fz);
    if(swxw == 0)
        printf("p.m.\n");
    else
        printf("a.m.\n");
    return 0;
}