too few arguments to function and can't be used as a function---- beginning C

Question

Hi i am a beginner, and I have this homework for my beginning C class. I keep getting errors for the program I wrote particularly with my function. Here's my program:

#include <stdio.h>
//Function Declarations
double obtainTemp (void);
**double convertTemp (double tempF, double tempR, double tempC, double tempK);**
void printResult (double tempF, double tempR, double tempC, double tempK);

int main (void)
{
    //Local Declarations
    double tempF;
    double tempR;
    double tempC;
    double tempK;
    double fahrenheit;
    double rankine;
    double celsius;
    double kelvin;

    //Calling the functions
    fahrenheit = obtainTemp ();
    rankine = convertTemp (tempR);
    celsius = convertTemp (tempC);
    kelvin = convertTemp (tempK);

    //will print it by...
    printResult (tempF, tempR, tempC, tempK);

    int temp;
    printf("Press anything to exit: ");
    scanf("%d", &temp);

    return 0;
}//main

//============obtainTemp===============
double obtainTemp (void)
{
       //Local Declarations
       double tempF;
       printf("Enter temperature: ");
       scanf("%lf", &tempF);

       return tempF;
}

//============convertTemp==============
int convertTemp (double tempF, double tempR, double tempC, double tempK);
{

       //Statements
       tempR = (tempF - 32) + 491.67;
       tempC = (tempF - 32) * 100/180;
       tempK = tempC + 273.16;

       return tempF, tempR, tempC, tempK;
}

//============printResult===============
void printResult (double tempF, double tempR, double tempC, double tempK)
{
     //Statements
     printf("The temperature is %lf degrees fahrenheit\n", tempF);
     printf("The value of %lf in rankine is %lf\n", tempF, tempR);
     printf("The value of %lf in celsius is %lf\n", tempF, tempC);
     printf("The value of %lf in kelvin is %lf\n", tempF, tempK);
     return;
}

This function below has too few arguments, and compiler says i can't use it as a function. why oh why?

double convertTemp (double tempF, double tempR, double tempC, double tempK);

Sorry, I am a beginner...i would really appreciate your help :)

Answer 1

The error is pretty clear, you're not calling the function the way it's supposed to be. The function takes 4 parameters, and you are only passing one.

But that is only your FIRST mistake. The SECOND, is that the function arguments as they are declared right now, will make a local copy of the parameters:

double convertTemp (double tempF, double tempR, double tempC, double tempK);

This means that inside the body of the function, changes on any of these variables will not propagate to the variables declared in main which you used to call convertTemp(). What I'm saying is at the time the function is called, another 4 variables are created on the stack and their values are copied from the variables you sent to the function.

There are two approaches to solve this problem:

• The first, a little more complex to understand if you don't know nothing about pointers. On this approach, in order to modify the original variables of main, you need to change your function signature to receive memory pointers instead:

  void convertTemp (double* tempF, double* tempR, double* tempC, double* tempK);

and the body of function needs to change too, in order to be consistent with the prototype declared in the beginning of the file:

void convertTemp (double* tempF, double* tempR, double* tempC, double* tempK)
{
       //Statements
       *tempR = (*tempF - 32) + 491.67;
       *tempC = (*tempF - 32) * 100/180;
       *tempK = *tempC + 273.16;
}

Note that the new function signature does not return any value (ie. void). This is not necessary since you will be operating directly on the variables passed by main().

On main(), you should call the function like:

fahrenheit = obtainTemp();
convertTemp(&fahrenheit, &rankine, &celsius, &kelvin);

• The second approach, since you are a beginner this is probably going to be easier for you to understand, is to declare 3 functions, one for each conversion you need to do:

double convertR(double value)
{
  return (value - 32) + 491.67;
}

double convertC(double value)
{
  return (value - 32) * 100/180;
}

double convertK(double value)
{
  return value + 273.16;
}

Then on main(), you would call them like:

fahrenheit = obtainTemp();
rankine = convertR(fahrenheit);
celsius = convertC(fahrenheit);
kelvin = convertK(fahrenheit);

printResult(fahrenheit, rankine, celsius, kelvin);