How to execute a C++ program while including variables from the function within the terminal

BDO 0
Viewed 36

I wrote a simple program to calculate the hypotenuse length of a triangle. My question is, how can I give variables "side1" and "side2" values while executing the main function from the terminal? Code below:

#include <iostream>
#include <cmath>

int main(int side1, int side2) {

    int c2 = (pow(side1, 2)) + (pow(side2, 2));
    
    std::cout << sqrt(c2) << std::endl;

    return 0;
}

The function compiles without error, so normally I would execute the function from terminal using "./main.exe", but is there a way to pass values to variables side1 & side2 while executing? (ex: ./main.exe "5" "5"). I don't want to go the std::cin route because I already know how to do that. For the same reason, I don't want to assign values to the variables within the function (ex: int side1 {5};).

I don't know if this is possible to do or not, but sites like Leetcode have their functions set up this way, and I have no clue how they input values for test cases.

c++
4 Answers

The signature of the main function can be

int main(int argc, char *argv[])

so you get an argument count and a "string" array. Note that argv[0] is the executable name, so side1 would be argv[1] and side2 is argv[2].

Thomas Weller0

As noted previously, your function signature for main is incorrect. The correct signature when you want to access command line arguments is:

int main(int argc, char **argv)

argc is the count of arguments, the first being the name of the executable. argv is an array of those arguments. We can:

  • Check that the right number of arguments have been passed in, and print an error if not.
  • Use std::atoi to convert those inputs into ints, at which point we can use them as we please.
#include <iostream>
#include <cstdlib>

int main(int argc, char **argv) {
  if (argc != 3) {
    std::cerr << "Usage: "<< argv[0] 
              << " val1 val2" << std::endl;
    return 1;
  }

  auto v1 = std::atoi(argv[1]);
  auto v2 = std::atoi(argv[2]);

  std::cout << v1 << ", " << v2 << std::endl;

  return 0;
}
userRb2210

You need to get the command line argument strings and convert them to integers. Alas, this does increase the complexity of your program a little if you want to catch errors.

#include <cmath>
#include <iostream>
#include <string>

int help()
{
  std::cerr << 
    "usage:\n"
    "  a.exe SIDE1 SIDE2\n\n"
    "Where SIDE1 and SIDE2 are integers.\n";
  return 1;
}

int main( int argc, char ** argv )
{
  int side1, side2;
  if (argc != 3) return help();
  try {
    side1 = std::stoi( argv[1] );
    side2 = std::stoi( argv[2] );
  }
  catch (...)
  {
    return help();
  }

  int c2 = side1*side1 + side2*side2;
  std::cout << std::sqrt( c2 ) << "\n";
}

You could leave a lot of that error checking out and just let the program crash without explanation, but IMHO it is always worth adding a usage clause to your program to help users (including yourself two months from now) figure out how to run the program.

Dúthomhas0
usernsZN0
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