[백준 1212] 8진수 2진수 (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("B1212_input.txt", "r", stdin);
    
    cin >> num;
    
    for(int i = 0; i < num.size(); i++)
    {
        if(num[i] == '0')
        {
            if(i == 0)
            {
                ans += "0";
            }
            else
            {
                ans += "000";    
            }
        }
        else if(num[i] == '1')
        {
            if(i == 0)
            {
                ans += "1";
            }
            else
            {
                ans += "001";    
            }
        }
        else if(num[i] == '2')
        {
            if(i == 0)
            {
                ans += "10";
            }
            else
            {
                ans += "010";    
            }
        }
        else if(num[i] == '3')
        {
            if(i == 0)
            {
                ans += "11";
            }
            else
            {
                ans += "011";    
            }
        }
        else if(num[i] == '4')
        {
            ans += "100";
        }
        else if(num[i] == '5')
        {
            ans += "101";
        }
        else if(num[i] == '6')
        {
            ans += "110";
        }
        else if(num[i] == '7')
        {
            ans += "111";
        }
    }
    
    cout << ans;
    
    return 0;
}