When the while loop starts the code stops calculating and outputting numbers - while-loop

Question

my code works the first time and when the loop start it stops calculating the numbers!
I want the program to ask the user to choose a material every time it finishes calculating the numbers. I used while (1!=2) { }
#include <iostream>
#include <stdio.h>
#include <math.h>
using namespace std;
float stress, strain, area;
double diameter;
long int F = 9900;
const float pi = 3.141593f;
int i = 0;
int main() {
char meterial;
cout << "This programm calculates the stress and strain of a rod under loads from 10000N to 20000N\n\n";
while (1!=2)
{
cout << "Choose the meterial of the rod\n\n";
cout << "S For STEEL\nA For ALUMINUM\nC For COPPER\nT For TITANIUM\n\n";
cin >> meterial;
switch (meterial)
{
case 's':
cout << "\nEnter the diameter of the rod in mm: ";
cin >> diameter;
area = (pi * diameter * diameter) / 4;
while (i <= 50)
{
stress = F / area;
strain = 200 / stress;
F = F + 100;
cout << "Load = " << F << " Stress = " << stress << " N/mm^2" << " Strain = " << strain << "\n";
i++;
}
break;
case 'a':
cout << "Enter the diameter of the rod in mm: ";
cin >> diameter;
area = (pi * diameter * diameter) / 4;
while (i <= 50)
{
stress = F / area;
strain = 69 / stress;
F = F + 100;
cout << "Load = " << F << " Stress = " << stress << " N/mm^2" << " Strain = " << strain << "\n";
i++;
}
break;
case 'c':
cout << "Enter the diameter of the rod in mm: ";
cin >> diameter;
area = (pi * diameter * diameter) / 4;
while (i <= 50)
{
stress = F / area;
strain = 117 / stress;
F = F + 100;
cout << "Load = " << F << " Stress = " << stress << " N/mm^2" << " Strain = " << strain << "\n";
i++;
}
break;
case 't':
cout << "Enter the diameter of the rod in mm: ";
cin >> diameter;
area = (pi * diameter * diameter) / 4;
while (i <= 50)
{
stress = F / area;
strain = 110.3 / stress;
F = F + 100;
cout << "Load = " << F << " Stress = " << stress << " N/mm^2" << " Strain = " << strain << "\n";
i++;
}
break;
default:
cout << "You entered a wrong character";
}
}
}
http://i.stack.imgur.com/do3qc.png

Answer 1

I don't see that you're resetting the value of i before the next call.
But you really should have that while loop (while (i <= 50)) in a function or method somewhere unless you have studied those yet.

Answer 2

The variable i is never re-initialized to zero. If you replace each
while (i <= 50)
statement in the cases for your switch statement with something like:
for (int i = 0; i <= 50; ++i)
and remove the i++; lines in each corresponding block, e.g.
case 's':
cout << "\nEnter the diameter of the rod in mm: ";
cin >> diameter;
area = (pi * diameter * diameter) / 4;
for (int i = 0; i <= 50; ++i) // while (i <= 50) <-- change
{
stress = F / area;
strain = 200 / stress;
F = F + 100;
cout << "Load = " << F << " Stress = " << stress << " N/mm^2" << " Strain = " << strain << "\n";
// i++; <-- remove
}
your code should do what you expect. You might consider replacing the while (1!=2) test with something like while(1) or for(;;), but only because those are more common idioms (your test will always evaluate to true so it's still just fine).
On Edit: one more thing - you never re-initialize F, but you modify it in your calculation. Each time you run through your switch statement, you're starting with a different initial value for F.