从键盘上读入一个整数，判断是几位数，并求各位之和。

#include <stdio.h>
#include <math.h>
int main(){
long a;
int digit = 0, sum = 0, buffer;
printf("Please key in the integer:\n");
scanf("%ld", &a);
do{
buffer = abs(a % 10);
a = a / 10;
sum += buffer;
digit++;
}while (a != 0);
printf("The integer you key in has %d digits.\n", digit);
printf("The sum of all the digits is %d.\n", sum);
}

Borland C下编译通过。此程序的缺点在于long型数据的储存长度，也就是超过了它的储存限制将会出错，解决办法是用一个array来储存，但比较麻烦。有问题请再问我