Question

I am doing a homework assignment that involves writing a program to draw shapes with ASCII characters and move them across the screen. In this example, I am trying to write a method to move a circle that has already been drawn. I know my drawCircle method works, however when I try to call the drawCircle method in my moveCircle method it does not print anything out.

void CircleType::drawCircle() const{
    for (int i = 0; i < NUMBER_OF_ROWS; i++) {
        for(int j = 0; j < NUMBER_OF_COLUMNS; j++) {
            int p = abs (x - j);
            int q = abs (y - i);
            int distance =  pow(p, 2) + pow(q, 2);
            int realDistance = pow(radius, 2);
            if (abs(realDistance - distance) <= 3){ // I tested out several values here, but 3 was the integer value that consistently produced a good looking circle
                drawSpace[i][j] = symbol;
            }
        }
    }
    displayShape();
    return;
}




bool CircleType::moveCircle(int p, int q){
    if (p - radius < 0 || p + radius > NUMBER_OF_COLUMNS){
        cout << "That will move the circle off the screen"<< endl;
        return false;
    }
    else if (q - radius < 0 || q + radius > NUMBER_OF_ROWS){
        cout << "That will move the circle off the screen"<< endl;
        return false;
    }
    else{
        x = p;
        y = q;
        for (int m = 0; m < NUMBER_OF_ROWS; m++){
            for(int n = 0; n < NUMBER_OF_COLUMNS; n++){
                if (drawSpace[m][n] == symbol)
                    drawSpace[m][n] = ' ';
            }
        }
        void drawCircle();
        return true;
    }

}

drawSpace is a 2D char array that holds the ASCII characters for the shape, and displayShape is a function that prints out that 2D array. As I said above, the drawCircle function works, however the moveCircle method does not. Am I calling the drawCircle method wrong when I try to use it in moveCircle.

Answer 1

void drawCircle();

That is not a function call; it is a function prototype declaration. To call the function, simply use

drawCircle();

A function prototype simply tells the compiler that a function with a certain signature exists. This allows you do do something like this (though this is not at all common to do in this way).

int main() {
    void Foo();
    Foo();
}

void Foo { /* whatever */ }

If the prototype were omitted the compiler would throw an error as Foo was not declared before its use. In a similar (and more common) vein you could also do this (called a forward declaration).

void Foo();

int main() {
    Foo();
}

void Foo { /* whatever */ }

Or just declare it first, but you don’t usually want a ton of functions before main.

void Foo { /* whatever */ }

int main() {
    Foo();
}