程序代码：

#include <stdio.h>
#include <string.h>
#define N 1000 + 10

int main() {
    int a[N] = {0}, b[N] = {0}, i, j, len, len1, len2, n, t;
    char s1[N], s2[N];
    scanf("%d", &n);
    for(t = 1; t <= n; t++) {
        if(t > 1) printf("\n");
        scanf("%s%s", s1, s2);
        len1 = strlen(s1);
        len2 = strlen(s2);
        for(i = len1 - 1, j = 0; i >= 0; i--) a[j++] = s1[i] - '0';
        for(i = len2 - 1, j = 0; i >= 0; i--) b[j++] = s2[i] - '0';
        len = len1 > len2 ? len1 : len2;
        for(i = 0; i < len; i++) {
            a[i] += b[i];
            if(a[i] >= 10) {
                a[i] %= 10;
                a[i+1]++;
            }
        }
        printf("Case %d:\n", t);
        if(a[len]) printf("%d", a[len]);
        printf("%s + %s = ", s1, s2);
        for(i = len - 1; i >= 0; i--) printf("%d", a[i]); printf("\n");
    }
    return 0;
}