#include <stdio.h>  
 
 void instructions();
 
void sqByRef(double *num);
void sqByVal(double num);
 
int main()
{
	FILE *inputfile;
	
	double inputNumber;   	/* variable holds a double */
	double *ptInputNumber;	/* variable holds the address of an address containing a 
double */
	
	ptInputNumber = &inputNumber; /* initalizing pointer so it can be used in scanf*/	

	instructions();
	
	inputfile = fopen("primes.txt", "r");
	
	while( fscanf(inputfile, "%lf", ptInputNumber)!=EOF)
	{
		printf("\n***********************************************");
		printf("\nFrom main function: input number => %.2f", *ptInputNumber);
		sqByVal(*ptInputNumber);
		printf("\nAfter passed by value: input number => %.2f", *ptInputNumber);
		sqByRef(ptInputNumber);
		printf("\nAfter passed by reference: input number => %.2f", *ptInputNumber);
	};
	
	printf("\n", inputNumber);
	
	fclose(inputfile);		
	return 0;
}

void sqByRef(double *num)
{	
	printf("\n\tPassed by reference:  %f squared is ", *num);
	*num = *num * *num;
	printf("%f", *num);
}

void sqByVal(double num)
{
	printf("\n\tPassed by value:  %.02f squared is ", num);
	num = num*num;
	printf("%.2f", num);
}

void instructions(void)
{
	printf("\n***********************************************************");
	printf("\n*****  This program pointer manipulation                ***");
	printf("\n*****                                                   ***");
	printf("\n*****  This program opens the file primes.txt,          ***");
	printf("\n*****  the data read in and printed to the screen.      ***");
	printf("\n*****  Then, the values will be passed to two functions ***");
	printf("\n*****  one by value, one by reference.                  ***");	
	printf("\n*****  Open and study the source code to see why the    ***");	
	printf("\n*****  values are different.                            ***");		
	printf("\n***********************************************************\n");
}