Re-entered value not returning to function

[connorc]

Hi I'm VERY new to C++ and am struggling to figure out what's wrong with my code. I'm doing a project to calculate the air density of a material which contain sphereical bubbles and cylindrical shapes pores. When I run the program and enter a negative value, I am prompted to enter a new value (as it should). However, when the calculations are performed, it uses the original negative value. So my code is only useful if I enter everything correctly.

Also if the number of pores or bubbles are zero, it should not ask me the radius of the bubbles or the radius/height of the pores. I'm not sure how to change it correctly.

Thanks for the help.

#include<iostream>
#include<iomanip>
#include<cstdlib>
#include<math.h>

float height, width, length;
float s_radius;
int bubbles;
int pores;
float c_radius, c_height;
float per;

//Namespace Declaration
using namespace std;


//Functions Prototypes
float check_inputs_of_Parallelepiped(float height, float width, float length);
float check_inputs_sphere(int bubbles, float s_radius);
void check_inputs_pores(int pores);
void check_inputs_cylinder(float c_radius, float c_height);
float Volume_of_sphere(float s_radius);
float Volume_of_cylinder(float c_radius, float c_height);
float percentage(float width, float length, float height, float c_height, float c_radius, float s_radius, int bubbles, int pores);

//Starting of main function

int main()

{

	//Asking for user inputs

	cout << "Enter the height, length, and width of the sample in centimeters: ";
	cin >> height >> width >> length;

	//call to function

	check_inputs_of_Parallelepiped(height, width, length);

	cout << endl;

	cout << "How many spherical bubbles are present?: ";
	cin >> bubbles;

	//call to function

	check_inputs_sphere(bubbles, s_radius);

	cout << "What is the radius of the spherical bubbles in centimeters?: ";
	cin >> s_radius;

	//call to function

	check_inputs_sphere(bubbles, s_radius);

	cout << endl;

	cout << "How many cylindrical pores are present? ";
	cin >> pores;

	//call to functions

	check_inputs_pores(pores);

	cout << "What are the radius and height of the cylindrical pores in centimeters? ";
	cin >> c_radius >> c_height;

	//call to functions

	check_inputs_cylinder(c_radius, c_height);

	cout << endl;

	//call to function

	per = percentage(width, length, height, c_height, c_radius, s_radius, bubbles, pores);

	//Display the percent air present in the meterial

	cout << "The material contains " << fixed << setprecision(3) << per << "% " << "air" << endl;

	cout << endl;

	return 0;

}

//function defination

float check_inputs_of_Parallelepiped(float height, float width, float length)
{

	float Volume;

	do

	{

		if (height<0)

		{

			cout << "The height of the sample must be greater then zero.\n";

			cout << "Please re-enter the height of the sample: ";

			cin >> height;

		}
	} while (height<0);


	do
	{
		if (length<0)

		{

			cout << "The length of the sample must be greater then zero.\n";

			cout << "Please re-enter the length of the sample: ";

			cin >> length;

		}
	} while (length<0);


	do

	{

		if (width<0)

		{

			cout << "The width of the sample must be greater then zero.\n";

			cout << "Please re-enter the width of the sample: ";

			cin >> width;

		}
	} while (width<0);

	//calculate volume

	Volume = width * height * length;

	return Volume;

}

//function defination

float check_inputs_sphere(int bubbles, float s_radius)

{
	do
	{
		if (bubbles<0)
		{
			cout << "The number of spherical bubbles must be greater than or equal to zero.\n";
			cout << "Please re-enter the number of spherical bubbles: ";
			cin >> bubbles;
		}
	} while (bubbles<0);


	do
	{
		if (s_radius<0)
		{
			cout << "The radius of the bubbles must be greater than or equal to zero.\n";
			cout << "Please re-enter the radius of the bubbles: ";
			cin >> s_radius;
		}
	} while (s_radius<0);

	return s_radius;

}

void check_inputs_pores(int pores)
{
	do
	{
		if (pores<0)
		{
			cout << "The number of cylindrical pores must be greater than or equal to zero.\n";
			cout << "Please re-enter number of cylindrical pores: ";
			cin >> pores;
		}
	} while (pores<0);
	
}


//function defination

void check_inputs_cylinder(float c_radius, float c_height)
{
	do
	{
		if (c_radius<0)
		{
			cout << "The radius of cylindrical pores must be greater than zero.\n";
			cout << "Please re-enter the radius of the cylindrical pores.";
			cin >> c_radius;
		}

	} while (c_radius<0);


	do
	{
		if (c_height<0)
		{
			cout << "The height of cylindrical pores must be greater than zero.\n";
			cout << "Please re-enter the height of the cylindrical pores.";
			cin >> c_height;
		}

	} while (c_height<0);

}

//function defination

float percentage(float width, float length, float height, float c_height, float c_radius, float s_radius, int bubbles, int pores)

{

	float VoS, VoC, per;

	VoS = Volume_of_sphere(s_radius);
	VoC = Volume_of_cylinder(c_radius, c_height);
	per = (VoS*bubbles + VoC*pores) * 100 / (height*width*length);

	return per;

}

//function defination

float Volume_of_sphere(float s_radius)

{

	float PI = 3.14159;
	float Volume;

	//calculating volume of sphere

	Volume = (4 * PI * pow(s_radius, 3)) / 3;

	return Volume;

}

float Volume_of_cylinder(float c_radius, float c_height)

{

	float PI = 3.14159;
	float Volume;

	//calculating Volume of Cylinder

	Volume = PI * pow(c_radius, 2) * c_height;

	return Volume;

}
 

[coder777]

The problem with the check_inputs_... functions is that you pass by value. I.e. you pass a copy of the value. Changing that copy will not affect the original value.

So pass the values by reference:

float check_inputs_of_Parallelepiped(float &height, float &width, float &length) // Note the reference operator &

If you want to check for invalid input (like "abc") which raises an error you need to use ignore like so:

http://en.cppreference.com/w/cpp/io/basic_istream/ignore

See the Example