Number to String

    1#include <bits/stdc++.h>
    2 
    3using namespace std;
    4 
    5int main(){
    6    ios::sync_with_stdio(0);
    7    cin.tie(0);
    8    string s;
    9    cin >> s;
    10    if (s.size() == 1 || s.find_first_not_of('0', 1) == -1) {
    11        cout << 0 << '\n';
    12        return 0;
    13    }
    14    int first = s[0] - '0' + 1;
    15    string want = to_string(first);
    16    for(int i = 0; i < s.length() - 1; i++){
    17        want.append("0");
    18    }
    19    int x = want.length(), y = s.length();
    20    vector<int> a(x), b(x, 0);
    21    for(int i = 0; i < x; i++){
    22        a[i] = want[x - 1 - i] - '0';
    23    }
    24    for(int i = 0; i < y; i++){
    25        b[i] = s[y - 1 - i] - '0';
    26    }
    27    for(int i = 0; i < x; i++){
    28        a[i] -= b[i];
    29        if (a[i] < 0) {
    30            a[i] += 10;
    31            a[i + 1]--;
    32        }
    33    }
    34    int pos = x - 1;
    35    //remove leading 0
    36    while(pos > 0 && a[pos] == 0){
    37        pos--;
    38    }
    39    string ans;
    40    while(pos >= 0){
    41        char temp = (char) (a[pos] + '0');
    42        ans.push_back(temp);
    43        pos--;
    44    }
    45    cout << ans << '\n';
    46}