#include "stdio.h"

struct time
{
    int hour;
    int minutes;
    int seconds;
};

int main( void )
{
    struct time timeupdate ( struct time now );
    struct currenttime，nexttime;
   
    printf ("enter the time ( hh: mm: ss )");
    scanf ("%i:%i:%i", &currenttime.hour, &currenttime.minutes, &currenttime.seconds );
   
    nexttime = timeupdate (currenttime);
    printf ("updated time is %.2i:%.2i:%.2i\n",nexttime.hour, nexttime.minutes, nexttime.seconds);
   
    return 0;
}

struct time timeupdate ( struct time now )
{
    
    ++now.seconds;
    if ( seconds == 60 ) {
        now.seconds = 0;
        ++now.minutes;
    
    if ( minutes == 60) {
        now.minutes = 0;
        ++now.hour;
        
        if ( now.hour == 24 ) {
            now.hour = 0;
        }
    }
    return now;
}

＝ ＝难道你自己不会调试么？自己动手吧，否则永远学不会东西的。

改过了：
#include <stdio.h>

struct time
{
    int hour;
    int minutes;
    int seconds;
}time;

struct time timeupdate ( struct time nows )
{
   
    ++nows.seconds;
    if ( nows.seconds == 60 )
    {
          nows.seconds = 0;
          ++nows.minutes;
    }
   
    if ( nows.minutes == 60)
    {
        nows.minutes = 0;
        ++nows.hour;
        }
        if ( nows.hour == 24 )
    {
            nows.hour = 0;
        }
    return nows;
}

int main()
{
    //struct time timeupdate ( struct time now );
    struct time currenttime;
    struct time nexttime;
    printf ("enter the time ( hh: mm: ss )\n");
    scanf ("%i:%i:%i", &currenttime.hour, &currenttime.minutes, &currenttime.seconds );
    nexttime = timeupdate (currenttime);
    printf ("updated time is %.2i:%.2i:%.2i\n",nexttime.hour, nexttime.minutes, nexttime.seconds);
    return 0;
}

  那些括号阿，小算法阿以后自己多注意点就行了。

同学太感谢你了~~我也不知道怎么回事，看了三遍就是看不出区别，太初心了