/*************************************
** proj3.c
**
** Dennis L. Frey
** 11/20/98
**
**  This program simulates a simple calculator
**
**  Possible input operations are
**	+ add
**	- subtract
**	* multiply
**	/ divide
**	^ exponentiation
** V or v absolute value
** R or r square root
** C or c clear running total
** E of e Exit
**
** Note that the main program does only "basic" or
** "high level" stuff.  The details are hidden in
** the functions
**
******************************************/

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

/* function prototypes
** these functions take the current total as the parameter
** and return the updated total
*/
double add (double a);
double subtract (double a);
double multiply (double a);
double divide (double a);
double exponent (double a);

main ()
{
   double total = 0;	/* the running total */
   int value;

   char command = ' '; 	/* holds user input -- initialized */
   char dummyc;		/* to accept the NEWLINES */
   int i;

   printf ("starting total is %0.2f\n\n", total);
   while (command != 'E' && command != 'e')
   {
	printf ("Input operation: ");
	command = getchar();	/* the real command character */
	dummyc = getchar();  	/* eat the NewLine */

	switch (command)
	{
		case '+':	/* addition */
			total = add (total);
			break;

		case '-':	/* subtraction */
			total = subtract (total);
			break;

		case '*':	/* multiplication */
			total = multiply (total);
			break;

		case '/':	/* division */
			total = divide (total);
			break;

		case 'C':
		case 'c':	/* clear total back to 0 */
			printf ("clearing the total\n");
			total = 0;
			break;

		case 'E':
		case 'e':  	/* exit */
			printf ("Exiting\n");
			break;

		case 'R':	/* square root */
		case 'r':
		    if (total < 0)
		    {
		       printf ("Can't take sqrt of negative number\n");
		    }
		    else
		    {
		        printf ("Taking Square Root of %0.2f\n", total);
			total = sqrt (total);
		    }
		    break;

		case '^':	/* raise total to power */
			total = exponent (total);
			break;

		case 'V':
		case 'v':	/* take the absolute value of total */
			printf ("Getting absolute value of %0.2f\n",
				total);
			total = fabs(total);
			break;

		default:	/* error for any other command */
			printf ("invalid command: %c\n", command);
			break;
		}
		printf ("subtotal = %0.2f\n\n", total);		
	}
	printf ("total is %0.2f\n", total);
}


/************************************************
** function add 
**	gets value from user and adds to parameter
**	returns new total to caller
****************************************************/
double add (double a)
{
    double value;
    printf ("Input value to add: ");
    scanf ("%lf", &value);

    /* eat the NEWLINE after the value */
    getchar(); 

    printf ("adding %0.2f to %0.2f\n", value, a);

    return value + a;
}

/************************************************
** function subtract
**	gets value from user and subtracts it from parameter
**	returns new total to caller
****************************************************/

double subtract (double  a)
{
    double value;
    printf ("Input value to subtract: ");
    scanf ("%lf", &value);	/* number to subtract */
    getchar();			/* eat the NEWLINE */
    printf ("subtracting %0.2f from %0.2f\n", value, a);

    return a - value;
}

/************************************************
** function multiply
**	gets value from user and multiplies times the parameter
**	returns new total to caller
****************************************************/
double multiply (double a)
{
    double value;
    printf ("Input multiplier: ");
    scanf ("%lf", &value);
    getchar();		/* eat the NEWLINE */
    printf ("multiplying %0.2f by %0.2f\n", a, value);
    return a * value;
}

/************************************************
** function divide
**	gets value from user and divides parameter by it
**	returns new total to caller
**
**	checks for divide by 0
****************************************************/
double divide (double a)
{
   double value;

   do {
        printf ("Input divisor: ");
	scanf ("%lf", &value);
	getchar();	/* eat the NEWLINE */
	if (value == 0)
	{
	    printf ("Can't divide by 0\n");
	}
    } while (value == 0);

    printf ("dividing %0.2f by %0.2f\n", a, value);
    return a / value;
}

/************************************************
** function exponent
**	gets value from user and raises parameter to
** that power using pow function from math library
**	returns new total to caller
****************************************************/
double exponent (double a)
{
    double value;

    printf ("Input exponent: ");
    scanf ("%lf", &value);
    getchar();			/* eat the NEWLINE */

    return pow (a, value);
}