Thread: Splitting a program in 3 files

Hello there!

I am new to C programming, so need you help with this. I have been given an assignment to create a simple calculator by splitting the program in 3 files. I was absent in this class so I am not sure how to go about doing this. It should have 2 .c files and 1 .h... I went through the internet extensively and could only come up with this. Please help me with the problem.

main.c:

Code:

//Calculator main.c


#include <stdio.h>
#include <conio.h>
#include "Functions.h"


int main()
{
	float x = 0, y = 0;
	int operation;
	char answer_calc = 'null';
	extern float a, b;
	
	do
	{
		printf("This is the main function!\n");
	
		printf("Enter the first number: ");
		scanf("%f", &x);
		
		printf("Enter the second number: ");
		scanf("%f", &y);
		
		printf("What do you want to perform?");
		printf("\n1. Addition");
		printf("\n2. Subtraction");
		printf("\n3. Division");
		printf("\n4. Multiplication");
		printf("\n!.	 Exit");
			
		printf("\nSelect the corresponding number only: ");
		scanf(" %c", &operation);
		
			if(operation == '1')
			{
				printf("The sum of the two numbers is: %d", addition(x, y));
			}
				
			else if(operation == '2')
			{
				printf("The difference of the two numbers is: %d", difference(x, y));
			}
			
			else if(operation == '3')
			{
				printf("The remainder of the two numbers is: %d", remainder(x, y));
			}
			
			else if(operation == '4')
			{
				printf("The product of the two numbers is: %d", product(x, y));
			}
			
			else if(operation == '!')
			{
				exit(0);
			}
			
			else
			{
				printf("Invalid option");
			}
			
			printf("\nDo you want to continue? (Y/N)");
			scanf(" %c", &answer_calc);
		
	} while ((answer_calc == 'y') || (answer_calc == 'Y'));
	


return 0;
}

Functions.c

Code:

#include "Functions.h"


extern float x, y;


float addition (float a, float b)
{
	return a + b;
}


float difference (float a, float b)
{
	return a - b;
}


float remainder (float a, float b)
{
	int rem;
	if (b == 0)
	{
		printf ("Cannot divide by 0 (ZERO)");
	}
	else
	{
		rem = a/b;
	}
	return rem;
}


float product (float a, float b)
{
	return a*b;
}

Functions.h

Code:

#ifndef FUNCTIONS_H_INCLUDED
#define FUNCTIONS_H_INCLUDED


float Sum(float a, float b);
float difference (float a, float b);
float remainder (float a, float b);
float product (float a, float b);


#endif

When I do a 'cl main.c' on the Developer Command window for VS2013, i get an error that reads :

main.obj
main.obj : error LNK2019: unresolved external symbol _difference referenced in f
unction _main
main.obj : error LNK2019: unresolved external symbol _product referenced in func
tion _main
main.obj : error LNK2019: unresolved external symbol _addition referenced in fun
ction _main
main.exe : fatal error LNK1120: 3 unresolved externals

I don't know VS, so this is only a guess, but have you tried running cl with the filenames of both .c files?

cl main.c Functions.c

Originally Posted by Matticus

I don't know VS, so this is only a guess, but have you tried running cl with the filenames of both .c files?

cl main.c Functions.c

It has worked! DAMMIT!

Now a new problem arises.. i changed all float to int now, and the calculator works just like how i expected. In my assignment, my mentor had asked us to use extern key word. I just need to know, if that is applicable here? meaning, can i user the extern key work 'somehow' or 'anyhow' here?

Thank you for the help

Well, I suppose you could declare a global variable for the result in "main.c", and extern it to "Functions.c", and have those math functions update that variable instead of returning their result.

I understand that the exercise is to learn the "extern" keyword, but be aware that actually implementing it that way is considered poor form. Your current implementation is better form - returning variables from the math functions. But as I said, it's probably just to get exposure to "extern".

I get it.. Thank you very VERY much! Have a nice day!

You're very welcome.