Why is my code showing a number like 3.09028e-41 and 1.01933e-038?-CodePudding

I'm currently working on a C program that can compute for thermal expansion of certain materials. Every time I enter the values, it keeps showing numbers like 1.01933e-038 and 3.09028e-41. Here's the code:

#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
using namespace std;


   string material_name;
   float temperature_change, length_of_material, displacement_in_meters, coefficient;

void theFormula(float temperature_change, float length_of_material, float coefficient) {
    displacement_in_meters = temperature_change * length_of_material * coefficient;

}
int main()
{
   char Continue;
   string material_name;
   float coefficient_steel = 1.20*pow(10,-5);
   float coefficient_concrete = 14.5*pow(10,-6);
   float coefficient_glass = 8.50*pow(10,-6);
   float coefficient_aluminum = 1.20*pow(10,-5);
   float coefficient_copper = 1.70*pow(10,-5);
   float coefficient_pyrex = 4.0*pow(10,-6);
   float temperature_change, length_of_material, displacement_in_meters, coefficient;

   do {

       cout << "What is the name of the material?" << "\n";
       cin >> material_name;
       transform(material_name.begin(), material_name.end(), material_name.begin(), ::toupper);
       cout << "What is the length of the " << material_name << "?" << "\n";
       cin >> length_of_material;
       cout << "What is the temperature change (in degrees celsius)?" << "\n";
       cin >> temperature_change;

       if (material_name == "STEEL") {
          theFormula(temperature_change, length_of_material, coefficient_steel);
          cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
       }
       else if (material_name == "PYREX") {
          theFormula(temperature_change, length_of_material, coefficient_pyrex);
          cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
       }
       else if (material_name == "COPPER") {
          theFormula(temperature_change, length_of_material, coefficient_copper);
          cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
       }
       else if (material_name == "CONCRETE") {
          theFormula(temperature_change, length_of_material, coefficient_concrete);
          cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
       }
       else if (material_name == "ALUMINUM") {
          theFormula(temperature_change, length_of_material, coefficient_aluminum);
          cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
       }
       else if (material_name == "GLASS") {
          theFormula(temperature_change, length_of_material, coefficient_glass);
          cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
       }
      else {
          cout << "The available options are: STEEL, PYREX, CONCRETE, GLASS, COPPER, and ALUMINUM.";
      }


  cout << "Type Y to continue, if not, type BYE." << "\n";
   cin >> Continue;
   }
   while (Continue == 'Y' || Continue == 'y');
   system("pause");
   return 0;
 }

I keep getting the same numbers no matter the values I put in. I checked the formula and the values for the coefficients, I can't seem to find what is wrong.

Edit:

Here is the edited version. I'm not just getting values of 0 instead of something like 0.0573048.

#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
using namespace std;

double theFormula(float temperature_change, float length_of_material, float coefficient) {
    return temperature_change * length_of_material * coefficient;
    }
int main()
{
   char Continue;
   string material_name;
   float temperature_change, length_of_material, displacement_in_meters, coefficient;
   displacement_in_meters = theFormula(temperature_change, length_of_material, coefficient);
   do {

       cout << "What is the name of the material?" << "\n";
       cin >> material_name;
       transform(material_name.begin(), material_name.end(), material_name.begin(), ::toupper);
       cout << "What is the length of the " << material_name << "?" << "\n";
       cin >> length_of_material;
       cout << "What is the temperature change (in degrees celsius)?" << "\n";
       cin >> temperature_change;

       if (material_name == "STEEL") {
          theFormula(temperature_change, length_of_material, 1.20E-5);
       }
       else if (material_name == "PYREX") {
          theFormula(temperature_change, length_of_material, 4.0E-6);
       }
       else if (material_name == "COPPER") {
          theFormula(temperature_change, length_of_material, 1.70E-5);
       }
       else if (material_name == "CONCRETE") {
          theFormula(temperature_change, length_of_material, 14.5E-6);
       }
       else if (material_name == "ALUMINUM") {
          theFormula(temperature_change, length_of_material, 2.31E-5);
       }
       else if (material_name == "GLASS") {
          theFormula(temperature_change, length_of_material, 8.50E-6);
       }
      else {
          cout << "The available options are: STEEL, PYREX, CONCRETE, GLASS, COPPER, and ALUMINUM.";
      }
  cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";
  cout << "Type Y to continue, if not, type BYE." << "\n";
   cin >> Continue;
   }
   while (Continue == 'Y' || Continue == 'y');
   system("pause");
   return 0;
 }

It's giving me a warning that the coefficient is uninitialized.

CodePudding user response：

You are declaring multiple variables with identical names. You assign to one variable but then use the other. That's why they have a garbage values.

One way to avoid this problem is not to use any global variables. Here's a quick example

// no global variables here


// theFormula returns a float
float theFormula(float temperature_change, float length_of_material, float coefficient) {
    // return the value, don't assign to a global variable
    return temperature_change * length_of_material * coefficient;
}

int main()
{

    ...

    // assign the returned value to a local variable
    displacement_in_meters = theFormula(temperature_change, length_of_material, coefficient_steel);
    // use the local variable
    cout << material_name << " will have a displacement of " << displacement_in_meters << "\n";

That a function can return a value seems to be something that newbies have trouble grasping, which then can lead to inappropriate use of global variables as in your case.