C++ :: Calculating Area And Perimeter

I am having trouble with my C++ program. My program asks the user to enter any number greater than 0 and less than 20, and if the user enters any number(s) outside the acceptable range, the output should display:

input outside of exceptable range > 0 and < 20
length: 1 width: 1 area: 1 perimeter: 1

But in my program, this output displays no matter what the user types (even if the numbers are in the acceptable range, when it should be displaying the length and width the user enters and also displaying the calculated perimeter and area whenever the user enters number(s) in the acceptable range. Here is my code:

#include <iostream>
using namespace std;

float class_rectangle_area();
float class_rectangle_perimeter();
float class_rectangle_length();
float class_rectangle_width();

[Code] .....