Thread: Ohm's Law Calculator Help (ALMOST COMPLETE)

Hello,

I have a lab assignment in an introductory programming class at the college course. The assignment is to create an ohm's law calculator.


The program should prompt the user for 4 different inputs, Resistance (in ohms), Potential difference (in Volts), Current (in Amps) and Power (in watts). The user must input at least two inputs. Valid inputs include any real number except for -1. If a -1 is inputted, your program should recognize that the variable containing the -1 is the variable that you are solving for. The following possibilities must be dealt with:

1. If less than two inputs are entered:

• Prompt the user “NOT ENOUGH DATA"

2. If two inputs are entered:

• Then calculate the other two values

3. If three inputs are entered:

• Verify that the three inputs are valid (i.e. if I, V & R are input, validate that I*R = V within 2%). If valid, then calculate the fourth variable. If not valid prompt the user “INVALID DATA” and end the program.
  
  

4. If Four inputs are entered:

• Verify that all four inputs are valid within 2%. If valid, prompt the user “VALID DATA” if not valid, prompt the user “INVALID DATA”.

I have written all of the program and it all works EXCEPT; I am having trouble getting the calculator to work if 4 inputs are entered. I feel that I have made a minor error but I am having trouble locating it. My code is attached. Help please!


Jason

Code:

#include <stdio.h>
#include <math.h>


int main (void)
{


float voltage , current , resistance, power, b, voltagecheck = 0, currentcheck = 0, resistancecheck = 0, powercheck = 0;


printf("OHMS LAW CALCULATOR \n");
printf("Enter voltage in volts \n");
scanf("%f", &voltage);


printf("Enter current in amps \n");
scanf("%f", &current);


printf("Enter resistance in ohms \n");
scanf("%f", &resistance);


printf("Enter power in watts \n");
scanf("%f", &power);






if ((voltage == -1) && (current == -1) && (resistance == -1))
    {
    printf("NOT ENOUGH DATA");
    goto ENDING;
    }
    else if ((voltage == -1) && (current == -1) && (power == -1))
    {
    printf("NOT ENOUGHT DATA");
    goto ENDING;
    }
    else if ((current == -1) && (resistance == -1) && (power == -1))
    {
    printf("NOT ENOUGHT DATA");
    goto ENDING;
    }
    else if ((voltage == -1) && (resistance == -1) && (power == -1))
    {
    printf("NOT ENOUGHT DATA");
    goto ENDING;
    }


if ((voltage == -1) && (power == -1))
    {
    voltage = current * resistance;


    power = pow(current, 2) * resistance;


    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if ((voltage == -1) && (current == -1))
    {
    voltage = sqrt(power * resistance);
    current = sqrt(power / resistance);
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if ((voltage == -1) && ( resistance == -1))
    {
    voltage= power / current;
    resistance = voltage / current;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if ((current == -1) && (resistance == -1))
    {
    current= power / voltage;
    resistance= voltage / current;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if ((current == -1) && (power == -1))
    {
    current= voltage / resistance;
    power= voltage * current;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if ((resistance == -1) && (power == -1))
    {
    resistance= voltage / current;
    power= voltage * current;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }




if ( voltage == -1)
    {
    voltage = current * resistance;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if (current == -1)
    {
    current= voltage / resistance;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if (resistance == -1)
    {
    resistance= voltage / current;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }
    else if (power == -1)
    {
    power = voltage * current;
    printf("voltage: %f. \n current: %f. \n resistance: %f. \n power: %f. \n" ,voltage, current, resistance, power);
    goto ENDING;
    }


if ((voltage != -1) && (current != -1) && (resistance != -1) && (power != -1))
{
    voltagecheck = (current * resistance);
    scanf("%f", &voltagecheck);


    currentcheck = (voltage / resistance);
    scanf("%f", &currentcheck);


    resistancecheck = (voltage / current);
    scanf("%f", &resistancecheck);


    powercheck = (voltage * current);
    scanf("%f", &powercheck);
 
}
    if ((voltagecheck < (voltage - (voltage * 0.02))) && (voltagecheck > (voltage + (voltage * 0.02))) && 
        (currentcheck < (current - (current * 0.02))) && (currentcheck > (current + (current * 0.02))) &&
        (resistancecheck < (resistance - (resistance * 0.02))) && (resistancecheck > (resistance + (resistance * 0.02))) &&
        (powercheck < (power - (power * 0.02))) && (powercheck > (power + (power * 0.02))))
    {
        printf("vofltagecheck: %f. \n currentcheck: %f. \n resistancecheck: %f. \n powercheck: %f. \n" ,voltagecheck, currentcheck, resistancecheck, powercheck);
        printf("VALID DATA");
    }
    
    else
    {
    printf("INVALID DATA");
    goto ENDING;
    }




ENDING:
scanf("%f",&b);
}

I'm using goto to get to the end of the program so that it doesn't print unnecessary information, if I understand your question correctly.

There are many better ways of structuring this program than using goto.

Also this looks very complicated even discounting the horrible goto statements.

Code:

   if ((voltage == -1) && (current == -1) && (resistance == -1))
   {
      printf("NOT ENOUGH DATA");
      goto ENDING;
   }
   else if ((voltage == -1) && (current == -1) && (power == -1))
   {
      printf("NOT ENOUGHT DATA");
      goto ENDING;
   }
   else if ((current == -1) && (resistance == -1) && (power == -1))
   {
      printf("NOT ENOUGHT DATA");
      goto ENDING;
   }
   else if ((voltage == -1) && (resistance == -1) && (power == -1))
   {
      printf("NOT ENOUGHT DATA");
      goto ENDING;
   }

Think about using a loop instead of the goto. After all you probably want to re-enter the data if you get improper input.

Jim

also you only NEED two inputs of data, ohms law and the power law will give you the other 2

My professor suggested i use goto, so I don't know what to tell you (this is an introductory course). Also, I know how Ohm's law works... it's ridiculous that I have to create a program that will handle 1-4 inputs but that is what the assignment calls for.

Yes I'm sure he said that. goto was not in my original program until he suggested I put it there to get rid of the duplicate print statements I was getting. Using a loop does make sense though. Assuming I implement one of the loop functions that still doesn't solve my problem with that I stated in my original post. Something has to be wrong with my final if statement. I understand using goto is sloppy but for the time being it is working.

Here is an example of your data entry that removes the goto:

Code:

   int repeat;
   do
   {
      repeat = 1;
      printf("OHMS LAW CALCULATOR \n");
      printf("Enter voltage in volts \n");
      scanf("%f", &voltage);

      printf("Enter current in amps \n");
      scanf("%f", &current);

      printf("Enter resistance in ohms \n");
      scanf("%f", &resistance);

      printf("Enter power in watts \n");
      scanf("%f", &power);

      if ((voltage == -1) && (current == -1) && (resistance == -1))
      {
         printf("NOT ENOUGH DATA");
      }
      else if ((voltage == -1) && (current == -1) && (power == -1))
      {
         printf("NOT ENOUGHT DATA");
      }
      else if ((current == -1) && (resistance == -1) && (power == -1))
      {
         printf("NOT ENOUGHT DATA");
      }
      else if ((voltage == -1) && (resistance == -1) && (power == -1))
      {
         printf("NOT ENOUGHT DATA");
      }
      else
      {
         printf("\nTry again\n");
         repeat = 0;
      }
   } while(repeat);

This just removes the gotos, nothing else. I didn't change any of your logic and it probably isn't an ideal solution but it does eliminate several goto statements.

Also note that comparing a floating point number with the == or != operators is not recommended. Floating point numbers are approximations.


Jim

wow EVERY programmer i know, and some prof`s from 5 different schools that i help tutor/teach with/for, simply says "goto is not part of programming, it is only left there because of old habits."

does your programming teacher actually program, or just got thrown into teaching C? lol