字符串解法

#include<bits/stdc++.h>
using namespace std;
void sub(string s1, string s2) {

int i = s1.size(), j = s2.size(), x = 0;
if (i < j || (i == j && s1 < s2)) {
    swap(s1, s2);
    swap(i, j);
    cout << "-";
}
string s = "";
while (i >= 1 || j >= 1) {
    int n1 = (i >= 1) ? s1[i-1] - '0' : 0;
    int n2 = (j >= 1) ? s2[j-1] - '0' : 0;
    int sum = n1 - n2 - x;
    if (sum < 0) {
        x = 1;
        sum += 10;
    }
    else x = 0;
    s = char(sum + '0') + s;
    i--, j--;
}
while (s[0] == '0' && s.size() > 1) s.erase(0, 1);
cout << s;

}
int main() {

string s1, s2;
cin >> s1 >> s2;
sub(s1, s2);
return 0;

}