Concatenate C-strings

#include <iostream>

using namespace std;

void concatStrings(char target[], const char source[]){

int targetIndex = 0;

while(target[targetIndex]){ /// while it's not the "\0" continue the loop,
                            /// otherwise break

    targetIndex++;

}

int sourceIndex = 0;

while(source[sourceIndex]){

    target[targetIndex] = source[sourceIndex];
    targetIndex++;
    sourceIndex++;

}

    target[targetIndex] = '\0';

    cout << "Size of target : " << targetIndex << endl;
    cout << "Size of source : " << sourceIndex << endl;

}


int main(){

    char string1[256];
    cin.getline(string1,128);

    char string2[128];
    cin.getline(string2, 128);

    concatStrings(string1, "-");
    concatStrings(string1,string2);

    cout << "\n" << string1 << endl;

    return 0;
}