Compile Error: Function does not take 1 arguments

Question

void displayCost();
double computeArea();
double roundCost();

int main()
{
    return 0;
}

void displayCost(string name, int size)
{
    double area = computeArea(size);

    cout << "Since a " << size << "-inch pizza covers" << area << "square inches, "
         << name << ", then a 12 cents per square inch, the cost will be" << 12*area
         << " - which rounds to" << roundCost();
}

double computeArea(int size)
{
    double radius = size/2;
    double area = pi*radius*radius;
    return area;
}

double roundCost(double price)
{
    double roundedCost = ceil(price*100)/100;
    return roundedCost;
}

It happens on the line at double area = computeArea(size); . I don't understand why it says I'm not passing an argument in when I clearly am.

Answer 1

double computeArea();
double area = computeArea(size);
double computeArea(int size) {

One of these things is not like the others, .. .

You need to fix your prototype (the first one) to match the actual function:

double computeArea(int);

And, of course, ditto for the other prototypes as well.

Answer 2

You are messing up your forward declarations, they also have to reflect the type of parameters of your function.

void displayCost(string, int);
double computeArea(int);
double roundCost(double);

Answer 3

C++ differs from C in that a forward declaration of a function must specify the number and types of arguments. Whereas in C

double computeArea();

means that there is some function called computeArea that returns double , in C++ it is the same as

double computeArea(void);

That is, it specifies that computeArea takes no arguments.

Presumably the difference is because C++ allows functions to be overloaded, whereas C doesn't.

Answer 4

You've declared computeArea to take exactly zero arguments in the prototype (above main). The fact that you've then defined it to take a double down below is beside the point. Inside main, you're calling it with an argument, which, according to the prototype, is wrong.