Bin string

#include <iostream>
#include <string>
#include <bitset>
#include <cmath>
#include <vector>

using namespace std;

const int BIT_LEN = 4;

string conStrBin(string s){
    string dest;
    for(int i = 0; i < s.size(); i++){
        dest += bitset<8>(s[i]).to_string();
    }
    return dest;
}

int bintoDec(string binstr, int istart){
    int tmp = 0;
    int iend = istart + BIT_LEN;

    for(int i = istart; i < iend; i++){
        int vi = binstr[i] - 48;
        int exponent = i - istart;
        int val = vi * pow(2, (BIT_LEN - 1) - exponent );
        tmp += val;
    }

    return tmp;
}

int main(int argc, char** argv){

    string input_string;
    cout<<"WORD : ";
    cin>>input_string;

    string bin_string = conStrBin(input_string);
    cout<< "BIN : " << bin_string << endl;

    int v_result_size = bin_string.size() / BIT_LEN;
    vector<int> v_result(v_result_size);

    for(int i = 0; i < v_result_size; i++){
      v_result[i] = bintoDec(bin_string, i * BIT_LEN);
    }

    cout<<endl;

    for(int i=0; i < v_result_size; i++){
        cout<< "-" << v_result[i] << "-";
    }
}