error: 'ballPosition' undeclared (first use in this function)

Question

I'm getting this problem where I get this error message;

error: 'ballPosition' undeclared (first use in this function)

This is my code

#include"raylib.h"

int main()
{
    const int screenWidth = 800;
    const int screenHeight = 450;

    InitWindow(screenWidth,screenHeight, "ArcadeGame");
    
    while(!WindowShouldClose())
    {
        ballPosition = GetMousePosition();
        BeginDrawing();
            DrawCircleV(ballPosition, 35, DARKBLUE);
             ClearBackground(RAYWHITE);
             
        EndDrawing();
    }
    
    CloseWindow();
    
    return 0;
}

I tried to look at some examples but it still wont work.

You need to declare `ballPosition`. You need to write the type of `ballPosition` before the first use of it, just like you did with `screenWidth`. What type does `GetMousePosition()` return? — 12431234123412341234123, Apr 14 '23 at 09:04
That's very basic C knowledge and it's explained on the first pages of virtually all C text books. — Jabberwocky, Apr 14 '23 at 09:24
@VladfromMoscow It's unclear if you have only been exposed to dynamically typed languages like Python or Javascript. — August Karlstrom, Apr 14 '23 at 10:26
If you truly don't understand why you get the error message, or what *declarations* and *definitions* are, then you need to take quite a few steps back, and start with a true beginners book or tutorial, which will teach you the very basics of C. — Some programmer dude, Apr 17 '23 at 06:38

score 1 · Answer 1 · answered Apr 14 '23 at 09:12

In C, every variable needs a defined type. When you declare or define a new variable, you have to give a type (there are some exceptions where int is used without a type given but that isn't relevant for now). You didn't specify a type for ballPosition, so the compiler doesn't know the type and and complains.

When you look at the source code of raylib.h, you see that GetMousePosition() returns a Vector2-type value, Vector2 is a struct and typedef defined in raylib.h. Therefore it makes sense to Vector2 as type for ballPosition. You can do that by writing the type Vector2 before ballPosition is used the first time in a scope;

August Karlstrom · Answer 2 · 2023-05-29T13:40:43.103

The C programming language is a so called statically typed language with explicitly typed variable declarations. This means that every variable has a fixed type which must be specified in a variable declaration. In this case we can see at line 1129 in https://github.com/raysan5/raylib/blob/master/src/raylib.h that the function GetMousePosition is declared as

RLAPI Vector2 GetMousePosition(void);  // Get mouse position XY

so it returns a value of type Vector2. Therefor you need to declare the variable ballPosition with this type:

#include"raylib.h"

int main(void)
{
    const int screenWidth = 800;
    const int screenHeight = 450;
    Vector2 ballPosition;

    InitWindow(screenWidth, screenHeight, "ArcadeGame");
    while (! WindowShouldClose()) {
        ballPosition = GetMousePosition();
        BeginDrawing();
        DrawCircleV(ballPosition, 35, DARKBLUE);
        ClearBackground(RAYWHITE);
        EndDrawing();
    }
    CloseWindow();
    return 0;
}

error: 'ballPosition' undeclared (first use in this function)

2 Answers2