Styjun

Just wondering if anyone can give me some advice regarding where I'm going wrong here. My program works OK if I run it as is, but as soon as I swap the commented line with the one below it, I get errors. My goal is to be able to use the commented line because I want to create a program which let's me pass a pointer to a function as an argument to another function, but so far I'm having no luck.

#include <iostream>
using namespace std;

double arith_op(double left, double right, double (*f)(double, double));
double addition(double left, double right);
double subtraction(double left, double right);
double multiplication(double left, double right);

int main()

  double left, right;
  int choice;
  double (*f[3])(double, double) = addition, subtraction, multiplication ;
  
  cout << "Enter 1 for addition, 2 for subtraction, 3 for multiplication "
       << "(-1 to end): " << endl;
  cin >> choice;

  while (choice != -1) 

    cout << "Enter a floating-point number: " << endl;
    cin >> left;

    cout << "Enter another floating-point number: " << endl;
    cin >> right;

    // double* result = arith_op(left, right, f[choice - 1](left, right));
     double result = f[choice - 1](left, right);

    if (choice == 1) 
      cout << left << " + " << right << " = " << result;
    
    else if (choice == 2) 
      cout << left << " - " << right << " = " << result;    
    
    else 
      cout << left << " * " << right << " = " << result;    
    
    cout << endl;

    cout << "Enter 1 for addition, 2 for subtraction, 3 for multiplication "
     << "(-1 to end): " << endl;
    cin >> choice;
  


double arith_op(double left, double right, double (*f)(double, double))

  return (*f)(left, right);


double addition(double left, double right)

  return left + right;

double subtraction(double left, double right)

  return left - right;


double multiplication(double left, double right)

  return left * right;

I should add that my end goal is to package the function arith_op and the other functions in a seperate file, then use them by including their prototypes with 'extern'. This may be an odd way to approach the problem - it's for an assignment, and they're always odd.

Thank you :)

Wade

Your problem is in the 3rd argument here

arith_op(left, right, f[choice - 1](left, right));

f[i](left, right) is calling the function to give a double, rather than passing the function pointer to arith_op. Simply remove the parameter list

arith_op(left, right, f[choice - 1]);

smacks head I feel stupid now. It works. Brilliant, thank you!

Sadly my program still doesn't actually get me full marks, but that's because we have to submit it using an automated online marking system. So if your format is not precisely correct, you'll lose marks even if the program actually works fine.

Post script - I also successfully moved my functions to a seperate file, as per the assignment instructions. It's telling me I didn't name my functions correctly, but the program works, which is what matters.