What's wrong with that function?

Question

It says that it's not declared. I don't understand why.
https://code.sololearn.com/cKwIG3HuR7kJ/?ref=app

Answer 1

It reads from top to bottom, by the time it gets to
u (x, y, z, p);

It hasn't seen the declaration yet so it has no idea what it is and gives you an error.

You can implement the function before main or use a protoype
the prototype lets the compiler know that a function exists somewhere.

Simply copy the function declaration and copy it above main and follow it with ; instead of {}

//Note the argument variable names are optional so
//int u (int, int, int, int);

int u (int a, int b, int c, int d);

int main()
{
//...
}

int u (int a, int b, int c, int d)
{
//...
}

Answer 2

Thanks guys! But I just found that my function is faulty. I have to fix it.

Answer 3

Put the function before the main function.