Looping/Repetition help

I've been trying to figure this out for the past couple days, but it seems to be defeating me. I'm just at the very beginning of learning C Programming and this is one of my assignments. I'm just having trouble with the looping part. In the assignment hand out it said to not use any relational operator (==, !=, >, >=, <, <=) in the condition test for the loop. I can't seem to do it any other way. Even when I do use it, it doesn't seem to stop right away. I put my "while" below where it displays the code numbers so it won't keep repeating every time.

I didn't want to post my actual code, so I just shortened it and changed some stuff.

this is the output I get (more or less). It doesn't want to stop when I put a 0 in at Enter amount or zero to stop. It always ask to enter the code as well.

1 - Code 1
2 - Code 2

Enter amount or zero to stop: x
Enter code: x
xx dollars = x


Enter amount or zero to stop: x
Enter code: x
xx dollars = x


Enter amount or zero to stop: 0
Enter code: 0
00 dollars = 0

Code:

#include <stdio.h>


const float num_1 = 1.234;
const float num_2 = 0.123;


int main()

{
        
// Declare Variables
        
        int code;
        float dollars,total;
        
            
// Input

        printf("\n");
        printf("1 - Code 1 (num_1)");
        printf("\n");
        printf("2 - code 2 (num_2)");
        printf("\n");
        printf("\n");
while (amount != 0) {   
        printf("Enter amount or a zero to stop: ");
        scanf("%f", &dollars);
        printf("Enter code: ");
        scanf("%d", &code);

// Calculations  
                
         if (code>0 && code<3)
        {
                if (code == 1)
                {
                total = amount * num_1;
                }
                else if (code == 2)
                {
                total = amount * num_2;
                }
                
        } // End if-else
                
// Print output

        switch (code)
        {
                case 1:
                        printf("%.2f dollars = %.2lf", USD, total);
                        break;
                case 2:
                        printf("%.2f USD = %.2lf ", USD, total);
                        break;
                
                default:
                        printf("Code %d is invalid.", code);
        } // End Switch
                
} // End While

return 0;
                
}

you could use while(myVariable) this evaluates to while true, so if you get a zero the loop will break, i think minus numbers would be an issue though

Okay, the my variable thing worked, but it is still asking to enter a code after I put in a 0 for the amount. I know it has to do something with putting a printf somewhere else right? I just can't seem to figure out where and still have the program run smoothly.

You could try to reorder the program, I guess that's what you mean by "putting a printf somewhere else". You'd have to have reading the 0 to stop the last thing in the loop.


A simpler way is to just test for 0 and break out of the loop:

Code:

while (amount != 0) {   
        printf("Enter amount or a zero to stop: ");
        scanf("%f", &dollars);
        if (!dollars) //equiv to if dollars != 0.0
              break;             
        printf("Enter code: ");
        scanf("%d", &code);

// Calculations  
                
         if (code>0 && code<3)
        {
                if (code == 1)
                {
                total = amount * num_1;
                }
                else if (code == 2)
                {
                total = amount * num_2;
                }
                
        } // End if-else
                
// Print output

        switch (code)
        {
                case 1:
                        printf("%.2f dollars = %.2lf", USD, total);
                        break;
                case 2:
                        printf("%.2f USD = %.2lf ", USD, total);
                        break;
                
                default:
                        printf("Code %d is invalid.", code);
        } // End Switch
                
} // End While
// execution will resume here after break 
return 0;
                
}

Your code snippet doesn't set the amount variable anywhere -- maybe missed because you didn't post your full code, but thought I'd point it out.

Yes, I've noticed that I did leave amount out in the code I posted. But in my actual full code everything works like it should now! thank you so much!