How to make a c++ program and will use the command line input and ls in that directory?

  c++, command-line, shell

My system is Ubuntu 20.04. Suppose I am in project directory and this directory contains these folders/files: test, hello.txt. I wrote the following program:-

#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;
int main(int argc, char* argv[]){
    const char* command = "ls" + argv[1];
    return 0;

And then I will test as first argument of the program while running it. I expected it will print all files and folders in test folder. But it gave me an error.
Can someone tell me, what is the error and how to fix it?

Source: Windows Questions C++