C语言入门问题

#include <stdio.h>
int main(void)
{
    char in[] = "1,2,3,15,30";  //输入的字符串，忽略输入过程
    char *p=in;
    int a,n,sum=0;
    while (*p)
    {
        if (sscanf(p,"%d%n",&a,&n) == 1)
        {
            sum += a;
            printf("%d ",a);
            p += n;
        }
        else
            ++p;
    }
    printf("\nsum=%d\n",sum);
    return 0;
}