#include<stdio.h>
#define SEC_PER_MIN 60


int main(void)


{        
        int sec,min,left;
        
        
        printf("Convert secconds to minutes and seconds!\n");
        printf("Enter the number of seconds (< = 0 to quit):\n");
        scanf("%d",&sec);
             while(sec > 0 )
                  {
                     
                     
                  min   = sec / SEC_PER_MIN;
                  left  = sec % SEC_PER_MIN;
                  printf("%d seconds is %d minutes, %d  seconds.\n",sec,min,left);
                  printf("Enter next value (<=0 to quit ):\n");
                  
                  scanf("%d",sec);
                  
                  
                  }
              printf("Done!\n");



}

你还是仔细比较下你两次scanf语句吧，这个问题应该自己能排解的，不必问。

好好比较看看

恩  2楼说的挺好的  都告诉你错那了 仔细看看

呃  明白了  晕

原来是这样的