[백준 1373] 2진수 8진수 (Math) (C/C++)

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <math.h>
using namespace std;
 
string num;
string ans;
 
int main(void)
{
//    freopen("B1373_input.txt", "r", stdin);
    
    cin >> num;
    
    if(num.size() % 3 == 1)
    {
        num = "00" + num;
    }
    else if(num.size() % 3 == 2)
    {
        num = "0" + num;
    }
    
    for(int i = 0; i < num.size(); i += 3)
    {
        if(num.substr(i, 3) == "000")
        {
            ans += "0";
        }
        else if(num.substr(i, 3) == "001")
        {
            ans += "1";
        }
        else if(num.substr(i, 3) == "010")
        {
            ans += "2";
        }
        else if(num.substr(i, 3) == "011")
        {
            ans += "3";
        }
        else if(num.substr(i, 3) == "100")
        {
            ans += "4";
        }
        else if(num.substr(i, 3) == "101")
        {
            ans += "5";
        }
        else if(num.substr(i, 3) == "110")
        {
            ans += "6";
        }
        else if(num.substr(i, 3) == "111")
        {
            ans += "7";
        }
    }
    
    cout << ans;
    
    return 0;
}