What does the C++ compiler error "looks like a function definition, but there is no parameter list;" mean?

Question

#include <iostream>
#include <fstream>

using namespace std;

int main
{
    int num1, num2;
    ifstream infile;
    ostream outfile;

    infile.open("input.dat");
    outfile.open("output.dat");

    infile >> num 1 >> num 2;

    outfile << "Sum = " << num1 + num2 << endl;

    infile.close()
    outfile.close()
    return 0;
}

This is what I did and when I compile it, I got this error that said

error C2470: 'main' : looks like a function definition, but there is no
parameter list; skipping apparent body

Please don't hate me :( I am new at this computer science....

Answer 1

I don't hate you. ♥

Functions have parameters, such as:

void foo(/* parameters here */);

If your function takes none you don't omit the list, but leave it empty or put void:

int main()
// or:
int main(void)

Which you use is up to you. I prefer explicitly stating void.

---

Note, there are other variants you'll encounter. This is the second most common variant:

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

It gives you a count of the arguments and what they were. Such as:

myExe andAOne andATwo andIDontHateYou

You would be able to access those arguments. There can be more, but that should cover it for now. Don't worry about that stuff till later. <3

---

Concerning your code:

int main(void) // no parameters
{
    int num1, num2;
    ifstream infile;
    ostream outfile;

    infile.open("input.dat");
    outfile.open("output.dat");

    infile >> num1 >> num2; // no spaces in you variable names

    outfile << "Sum = " << num1 + num2 << endl;

    infile.close(); // missing semicolon
    outfile.close(); // missing semicolon

    return 0; // fun fact: optional. In C++, return 0 in main is implicit
}

That should get you started.

---

The rest of this may not make sense, and that's okay. I'm merely including it for completeness. If it doesn't make sense, ignore it for now:

int main(void)
{
    ifstream infile("input.dat"); // use the constructor to open it
    ostream outfile("output.dat");

    int num1, num2; // don't declare variables until you need them
    infile >> num1 >> num2;

    outfile << "Sum = " << num1 + num2 << endl;

    // closing is done automatically in the destructor of the fstream
}

Answer 2

You forgot the parentheses which are required for a function definition. Change that to:

int main()
{
    ...
}

Answer 3

You're missing parentheses after main.

Also, semicolons:

infile.close();
outfile.close();