How to terminate in loop? Help

[Zijing Ky]

  float i, R, I; // counter, resistance, input//
        float V; // voltage//


        printf("Enter the current: ");
        scanf("%f",&I);






        while ( R != -1) {


                 
                printf("Enter the resistance: " );
                scanf("%f",&R);
                V= R * I;
                printf("Voltage is %f\n", V);
        }


        return 0;

The question is to write a program that will input resistance R, current I for serval resistors, and will calculate and display the voltage for each resistor. The loop will terminate if your enter -1 as the resistance value. (Note that your program should output nothing when -1 is entered as the resistance value)
I want it to do nothing when I enter -1 for resistance but for this one it calculates the voltage. So what should i do?

[camel-man]

You could simply put

 if(R!=-1){
              V= R * I;
              printf("Voltage is %f\n", V);
              }

[Zijing Ky]

But that gives me infinite loop of 00000

[camel-man]

post your new code. You might have put that statement in the wrong place.

[Zijing Ky]

Wait you dont need to use loop for this?

[camel-man]

You tell me... Its your assignment, what are you trying to achieve?

[Zijing Ky]

OH i editted the starter post.

[Matticus]

When you begin the loop, R has no value (is not initialized) so it's likely that the loop will never execute.

Also, if the user enters -1 within the loop, the voltage is still calculated and printed before execution returns to the "while()" evaluation, so the rules of your assignment are not satisfied. "(Note that your program should output nothing when -1 is entered as the resistance value)"

[camel-man]

while( R != -1) 
                           {
                            printf("Enter the resistance: " );
                            scanf("%f",&R);
                           if(R!=-1){
                                      V= R * I;
                                      printf("Voltage is %f\n", V);
                                       }
                         }

How does this give you an infinite loop?

[Zijing Ky]

while( R != -1) 
                           {
                            printf("Enter the resistance: " );
                            scanf("%f",&R);
                           if(R!=-1){
                                      V= R * I;
                                      printf("Voltage is %f\n", V);
                                       }
                         }

How does this give you an infinite loop?

oh 'cause I didn't add it in, i just replaced it.. Silly me.

[Matticus]

declare and initialize variables

prompt for resistance
while (resistance is not -1)
    calculate and print voltage
    prompt for resistance

[Zijing Ky]

Ok it works! Thanks!!

[Matticus]

Take this as a lesson in structuring your logic to neatly accomplish your goals. Figure it out step by step, on paper beforehand if need be.