Implementation of the analogue of strcat () in c ++

Question

C++ / C#

Hello. I am a beginner in c ++ programming, and in the training literature I met the task of writing my own analogue of the strcat () function. I accepted the challenge and this is what happened:

#include <iostream>
#include <cstdio>
#include "stdafx.h"
#include "conio.h"

using namespace std;

void add(char *some, char *some2);
int main(){
  setlocale(0, "");
  char some[80] = "Слово";
  char some2[80] = "Второе";
  add(some, some2);
  cout << some << "\n";
  system("pause");
  return 0;
}
void add(char *some, char *some2){
  int first_length = strlen(some);
  for (int i = 0; i < strlen(some2); i++){
    *(some + first_length + i) = *(some2 + i);
  }
}

I would like to know:
1) How normal is my solution in terms of performance
2) How can I make it shorter and faster
3) And in general, the mistakes I made.
Thanks in advance for your replies.

Answer 1

Huge minus - what will happen if the length of some is 79 characters? Where will some2 be copied to?
The second huge minus - what will be the length of the string in the above example after concatenation?
You didn't write a trailing 0 to the resulting string.
The big minus is the recomputation of pointers and the length of some2 in each iteration of the loop. The initial values ​​must be calculated before the loop, only increment / decrement should be done in the loop.
A small minus - it makes no sense to count the length of some2. It is enough just to go to the symbol with code 0.