#include<stdio.h>
#define SEC 60
int main(void)
{
    int sec,min,left;

    printf("Convert seconds to minute an seconds!\n");
    printf("Enter the number of seconds(<=0 to quit);\n");
    scanf("%d",&sec);
    while(sec>0)
    {
        min=sec/SEC;
        left=sec%SEC;
        printf("%d seconds is %d minutes, %d seconds.\n",sec,min,left);
        scanf("%d",&sec);
    }
    printf("Done!\n");
    return 0;
}
求大神解释啊！主要就是不明白下面这里是如何实现的  
printf("Enter the number of seconds(<=0 to quit);\n");
    scanf("%d",&sec);
谢谢了