大数加法

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

void reverse_str(char *pBegin, char *pEnd){
    while(pBegin < pEnd){
        char t = *pBegin;
        *pBegin = *pEnd;
        *pEnd = t;
        ++pBegin;
        --pEnd;
    }   
}

bool add(const char *pA, const char *pB, char *pSum, int maxSumLen){
    if(pA == NULL || pB == NULL || pSum == NULL || maxSumLen <= 0){ 
        return false;
    }   
    int lenA = strlen(pA);
    int lenB = strlen(pB);
    int k = 0;
    pSum[k] = 0;
    for(int i = lenA - 1, j = lenB - 1; (k <= maxSumLen - 2 && (i >= 0 || j >= 0)); i--, j--, k++){
        int a = i >= 0 ? pA[i] - '0' : 0;
        int b = j >= 0 ? pB[j] - '0' : 0;
        pSum[k] += a + b;
        pSum[k + 1] = pSum[k] >= 10 ? pSum[k] / 10 : 0;
        pSum[k] = pSum[k] % 10 + '0';
    }   
    pSum[k] = '\0';
    reverse_str(pSum, pSum + k - 1); 
    return true;
}

int main(){
    char strA[] = "123499999";
    char strB[] = "223999999";
    char strSum[10];
    add(strA, strB, strSum, 10);
    printf("strA:%s, strB:%s, strSum:%s\n", strA, strB, strSum);
    printf("result:%d\n", atoi(strSum)  == (atoi(strA) + atoi(strB))%1000000000);
    return 0;
}