题解 | #Integer Inquiry#

#include <string.h>
#include <algorithm>
#include <iostream>
#define MAX_DIGITS 1000
using namespace std;

void add(char a[], char b[], char c[]) {
    int alen = strlen(a), blen = strlen(b);
    c[max(alen, blen)] = '\0'; 
    int carry = 0, sum = 0;
    int i, j;

    for (i=alen-1, j=blen-1; i>= 0 || j>=0; i--, j--) {

        int adigit = (i >= 0 ? a[i] - '0' : 0); //converting char 'i' to int i
        int bdigit = (j >= 0 ? b[j] - '0' : 0);
        sum = adigit + bdigit + carry;
        carry = sum / 10;
        c[max(i, j)] = sum % 10 + '0';
    }

    if(carry == 1){ //最高位进位
        for(int k=strlen(c)+1;k>=1;k--)
            c[k]=c[k-1];
        c[0]='1';
    }
}

int main(void) {
    char a[MAX_DIGITS], b[MAX_DIGITS], c[MAX_DIGITS];
    scanf("%s", a);
    scanf("%s", b);
    add(a, b, c);
    while(scanf("%s", a)!=EOF){
        memcpy(b,c,sizeof(c));
        add(a, b, c);
    }
    printf("%s", c);
    return 0;
}