ahh need massive help with this C++ program dealing with calculation of volume/area

Write a program that calculates area/volume of various shapes.
1st call function w/ prototype: void showMenu(int &); which displays menu

this is what the output should be:
Attachment 12599

this is what i have so far... yeah, fairly lost

// This program is designed to allow the user to calculate the area and volume of various shapes.

#include <iostream>
#include <iomanip>

using namespace std;

void showMenu (int &);
double area (double length, double width);
double area (double radius);
double volume (double length, double width, double height);
double volume (double radius);

int main()
{
int selection;

double length;
double width;
double height;
double radius;

cout << fixed << showpoint << setprecision(2);

cout << "1. Calculate the area of a rectangle" << endl;
cout << "2. Calculate the area of a circle" << endl;
cout << "3. Calculate the volume of a box" << endl;
cout << "4. Calculate the volume of a sphere" << endl;
cout << "5. Quit" << endl;
cin >> "Please select 1-5: " >> selection;
cout << endl;

What is exacly your doubt?

kinda dunno where to go from here; i'll try to make more advances in the program and find my doubts

I'll start by pointing out this obvious error:

Code:

---

cin >> "Please select 1-5: " >> selection;

---

This cannot happen. Cin is supposed to 'read' the user's input. Cout is what the console prints so I'd change it to this.

Code:

---

cout<<"Please select 1-5";
cin>>selection;

---

As for the following code:

Code:

---

void showMenu (int &);

---

That's a function prototype.
When you define a function after your main code, then you must have a prototype before the main code so it can know it has been defined later on.
It should have the following structure:

Code:

---

void showMenu(int &)  //<--- Prototype

int main()
{
      showMenu(int &)
      (.........);
}

void showMenu(int &)  //<-- Your function defined
{
    (.....);
}

---

OR

Code:

---

void showMenu(int &)  //<-- The function has been defined before main so prototype is not required
{
    (.......);
}

int main()
{
    showMenu(int &);
    (...........);
}

---

If I was you I'd make a function for each option. One to compute a rectangle area, another for a circle area etc and then call each one of them depending on the user input (1-5).

Btw, the function call is wrong.
Instead of

showMenu(int &);

do

showMenu(your_favorite_int_variable_here);