高精度减法，下面代码的memset函数有什么作用？为什么删掉输出就会乱码？

Question

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int main()
{
    int a[256], b[256], c[256], lena, lenb, lenc, i;
    char n[256], n1[256], n2[256];
    memset(a, 0, sizeof(a));
    memset(b, 0, sizeof(b));
    memset(c, 0, sizeof(c));
    printf("Input minuend:");
    gets_s(n1);
    printf("Input subtrahend:");
    gets_s(n2);
    if (strlen(n1) < strlen(n2) || strlen(n1) == strlen(n2) && strcmp(n1, n2) < 0)
    {
        strcpy_s(n, n1);
        strcpy_s(n1, n2);
        strcpy_s(n2, n);
        cout << "-";
    }
    lena = strlen(n1);
    lenb = strlen(n2);
    for (int i = 0; i <= lena - 1; i++)
        a[lena - 1] = int(n1[i] - '0');
    for (int i = 0; i <= lenb - 1; i++)
        b[lenb - 1] = int(n2[i] - '0');
    i = 1;
    while (i <= lena || i <= lenb)
    {
        if (a[i] < b[i]) {
            a[i] += 10;
            a[i + 1]--;
        }
        c[i] = a[i] - b[i];
        i++;
    }
    lenc = i;
    while ((c[lenc]) == 0 && lenc > 1)
        lenc--;
    for (i = lenc; i >= 1; i--)
        cout << c[i];
    cout << endl;
    system("pause");
    return 0;
}

Answer 1

作用是将abc三个数组的每个元素都设置为0
否则没有赋值的地方都是随机的值，自然计算出来就不对了。