usin swap, need to turn positive number into negative

[Ausha]

Hi again! now i need to turn positive number into negative using swap. program should look something like this, i have to use prototype, just the issue is, to determine '-'. right now this is not working properly.

  #include<iostream>

using namespace std;

void swap(int a, int b)
{
a=b;
b=(-a);
}
int main()
{
    int c, b;
    
cin>>c;

    swap(c,b);
    cout<<c<<endl;
    system ("pause");
    return 0;
}

[machinafour]

There is no assignment of c or b in your code.

Why does swap need 2 parameters?

How about this?

#include<iostream>
using namespace std;

int swap(int a)	
{	
	return 0 - a;
}
	
int main()
{
        int a;
	
	cout << "Enter a positive number: ";    
	cin >> a;

    a = swap(a);	
    cout << a << endl;
    system ("pause");
	return 0;
}

[Ausha]

swap can only work with 2 parameters, thats the essence of this function I guess, maybe im wrong, but Your code is not working either.

[machinafour]

It's working fine for me! What error messages are you getting for my code?

[Ausha]

oh it is working, i must have copypasted something wrong :)

[Ausha]

can You please explain? why is this working only when this line is like this a = swap(a);? and if you remove a= than it gives you same positive number back?

[machinafour]

Because swap returns an integer (the negative version of the parameter).

a = swap(a); assigns the value returned by swap to the variable a.

swap(a) alone will pass a to swap() but nothing will be returned, the a within swap() is a different local variable to the a in main(), the a in swap() is modified but not the a in main().

Maybe it's clearer if we call the swap() parameter x instead?

#include<iostream>
using namespace std;

int swap(int x)	
{	
	return 0 - x;
}
	
int main()
{
        int a;
	
	cout << "Enter a positive number: ";    
	cin >> a;

    a = swap(a);	
    cout << a << endl;
    system ("pause");
	return 0;
}

[Ausha]

You've been a great help! Thank you a lot!