Variables in main()

[valthyx]

int main()
int x = 5;
int add(int a, int b)
{
    return a+b+x;
}

I got an error, saying that the "x" in the add function is not declared. It is legal in C, but not in C++. May i know why? Also, how could I used the "x" of main() in add()?

[manasij7479]

err...Where is main() 's body?
Do you really think this code is legal in C?

Also, how could I used the "x" of main() in add()?

Pass it by reference.

[valthyx]

Sorry, i was typing an example without realising that i didnt put the braces for the main().

int main()
{
    int x = 5;
    int add(int a, int b)
    {
        return a+b+x;
    }
}

By the way, can i have a simple example based on this example

[grumpy]

C is not pascal. One consequence is that functions cannot be implemented inside the bodies of other functions.

[valthyx]

Why in C, there is no problem calling a variable from main() in add(), where add() is inside main()? Why is it illegal is C++?

[manasij7479]

The closest you can come to that is..

#include<iostream>
int main()
{
    int x = 5;
    int add(int,int,int&);
    std::cout<<add(2,4,x)<<std::endl;
    std::cout<<x; //To show that x really changes
    
    
}
int add(int a, int b, int& x)
{
    x-=4;
    return a+b+x;
}

[Elysia]

Why in C, there is no problem calling a variable from main() in add(), where add() is inside main()? Why is it illegal is C++?

This is not legal C, either. A function cannot be encapsulated in another function.

[grumpy]

Why in C, there is no problem calling a variable from main() in add(), where add() is inside main()? Why is it illegal is C++?

Your code is invalid because add() is implemented in the body of main(). That is illegal in both C and C++.

If you have something that is apparently working when compiled as C, and not when compiled as C++, then it is different from the code you have posted here.

[msh]

If this code is legal for you, then your C compiler is brain-dead. Put it out of our misery and get a new one.

[valthyx]

Thanks for the reply, I got it.

[Salem]

GCC allows nested functions.
Using and Porting the GNU Compiler Collection (GCC): C Extensions

Why it does is another matter entirely.