Problem Setting a char to exit program

bostero22 · #1 01-Nov-2008, 16:29

Hello, i want this program to exit when the user enters Q or q ... but for some reason when i enter Q or q the program goes into an infinite loop... can someone help me?

CPP / C++ / C Code:


#include <cstdlib>
#include <iostream>


using namespace std;

void terminator();

int main(int argc, char *argv[])
{
    
    double temperature;
    char Q, q;
    
    
    
    cout << "This program will ask the user for a certain temperature and it will \n";
    cout << "let the user know if either water, mercury, oxygen, or ethyl alcohol\n";
    cout << "would freeze or boil at that temperature\n";
    cout <<"Enter exit to finish the program\n\n\n";
    
        
    while (temperature != 'Q' || temperature != 'q')
          {
               cout << "Please, Enter a temperature: \n";
               cin >> temperature;
               
               if (temperature <= -362 )
               cout << "At this temperature: water, mercury, oxygen, and ethyl alcohol will freeze\n";
                    
               if (temperature <= -173 && temperature >= -306){
               cout << "At this temperature: water, mercury, and ethyl alcohol will freeze\n";
               cout << "Oxygen will boil.\n";}
               
               if (temperature <= -306 && temperature > -362)
               cout << "At this temperature: water, mercury, and ethyl alcohol will freeze\n";
               
               if (temperature <= -38 && temperature > -173){
               cout << "At this temperature: water and mercury will freeze\n";
               cout << "Oxygen will boil.\n";}
               
               if (temperature <= 32 && temperature > -38){
               cout << "At this temperature: water will freeze\n";
               cout << "Oxygen will boil.\n";}
               
               if (temperature > 32 && temperature < 172)
               cout << "At this temperature: oxygen will boil\n";
                
               if (temperature >= 172 && temperature < 212)
               cout << "At this temperature: oxygen and ethyl alcohol will boil\n";
                
               if (temperature >= 212 && temperature < 676)
               cout << "At this temperature: oxygen, ethyl alcohol, and water will boil\n";
                
               if (temperature >= 676)
               cout << "At this temperature: oxygen, ethyl alcohol, water, and mercury will boil\n";
                           
               
          }
          
          terminator();
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

void terminator()
     {
                  cout << "Have a nice day!" << endl;
                  
     }

ocicat · #2 01-Nov-2008, 17:03

Quote:

Originally Posted by bostero22

CPP / C++ / C Code:

    double temperature;
    char Q, q;
         
    while (temperature != 'Q' || temperature != 'q')
          {

It is a bad idea to test for a condition without either initializing or assigning the value which is being tested. You are banking on the fact temperature is not 'Q' or 'q'.
Secondly, temperature is defined as a double. What do you expect will happen if a char is assigned?

Lastly, given that you are doing a number of computations before wanting to break out of the loop, this is situation in which a do-while loop is warranted:

CPP / C++ / C Code:

#include <iostream>

using namespace std;

int
main() {
    char c;

    do {
        int i;

        cout << "input integer value: ";
        cin >> i;
        cout << i << " was received.  Continue?";
        cin >> c;
    } while (tolower(c) != 'q');

    return 0;
}

Lastly, when questions like this come up (& they come up for everybody...), take the time to reduce the problem down to the smallest case which still duplicates the same problem. If the fix isn't evident, you will have a clearer understanding of what still needs to be resolved.

bostero22 · #3 01-Nov-2008, 17:25

thanks I got it to work right

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Problem Setting a char to exit program

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Re: Problem Setting a char to exit program