/* Julie Kapsa
   Calculator Program to illustrate top down design
   File: calculat.cpp
   Lab 7               */

#include <iostream.h>

  /*
  Input:  Values and operations to be performed on these values.
  Output: The result of the calculations
  Purpose: to simulate a 6 function integer calculator Program.
  */

// function prototypes
void print_description();
int get_first_value();
int get_second_value();
char get_operation();
int  perform_calculation(int, int, char);
int  add(int, int);
int  subtract(int, int);
int  multiply(int, int);
int  exponent(int, int);

/* Beginning of Main */
void main()
  {
  int value1 = 0,    // first value
      value2 = 0,    // second value
      result = 0;    // result after operation performed
  char op = ' ';     // operation to perform

  print_description();

	value1 = get_first_value();

	op = get_operation();

  // Continue processing values until user indicates
  // ready for result
  while (op != '!')
    {
		value2 = get_second_value();
    result = perform_calculation(value1, value2, op);
		op = get_operation();
    value1 = result;
    }
  }

/**************************************************************/
//  Input:   None
//  Output:  To the screen
//  Purpose: Print the directions for the calculator

void print_description()
  {
  cout << "\n\nThis program simulates a four function calculator.";
  cout << "\nPlease use only integer values.";
  cout << "\nValid operations are:";
  cout << "\n\t'+' -- addition";
  cout << "\n\t'-' -- subtraction";
  cout << "\n\t'*' -- multiplication";
  cout << "\n\t'^' -- exponentiation";
  cout << "\n\t'!' -- exit program\n";
  } // end print_description

/**************************************************************/
//  Input:   None
//  Output:  Returns updated value
//  Purpose: Prompt for the first value to perform the operation on.

int get_first_value()
	{
	int value;
	cout << "\nEnter first value: ";
	cin >> value;
	return (value);
	}

/**************************************************************/
//  Input:   Character representing the operation
//  Output:  Updated operation
//  Purpose: Prompt the user and obtain valid operation

char get_operation()
	{
	char operation;

	cout << "Enter operation (+,-,*,^,!): ";
	cin >>  operation;

	// keep prompting until a valid operation is entered.
	while ((operation != '+') && (operation != '-') &&
	 (operation != '^') && (operation != '*') &&
	 (operation != '!'))
		{
		cout << "\nInvalid Operation. Please enter '+','-','^','!': ";
		cin >> operation;
		}

	 return (operation);
	} // end get operation

/**************************************************************/
//  Input:   Integer representing the second value
//  Output:  Returns updated value
//  Purpose: Prompt for a second value to perform the operation on.

int get_second_value()
	{
	int value;

	cout << "Enter value: ";
	cin >> value;
	return(value);
	} // end get_second_value

/**************************************************************/
//  Input:   Two integer values and a character operation
//  Output:  Integer result & print result to the screen
//  Purpose: Perform the given operation on the two values and
//	     return the result.

int perform_calculation(int val1, int val2, char operation)
	{
	int answer = 0;   // local answer -- needs to be returned

	// perform the appropriate operation
	switch (operation)
		{
    case '+'	: answer = add(val1, val2);
      break;
    case '-'	: answer = subtract(val1, val2);
      break;
    case '*'	: answer = multiply(val1, val2);
      break;
    case '^'	: answer = exponent(val1, val2);
    }

  cout << "\nResult = " << answer << "\n";

  return(answer);
  }  // end perform_calculation

/**************************************************************/
//  Input:   Two integer values
//  Output:  Return result of adding the two numbers
//  Purpose: Perform addition on two numbers

int add(int valu1, int valu2)
  {
  return (valu1 + valu2);
  } // end of add

/**************************************************************/
//  Input:   Two integer values
//  Output:  Return result of subtracting two numbers
//  Purpose: Subtract two numbers

int subtract(int valu1, int valu2)
  {
  return(valu1 - valu2);
  } // end of subtract

/**************************************************************/
//  Input:   Two integer values
//  Output:  Return result of multiplying two numbers
//  Purpose: Multiply two nubers

int multiply (int valu1, int valu2)
  {
  return(valu1 * valu2);
  } // end multiply

/**************************************************************/
//  Input:   Two integer values
//  Output:  Return result of raising 1st value to the
//	     second value.
//  Purpose: Raise one value to another

int exponent (int valu1, int valu2)
  {
  int answ = 1;   // local answer

  // continue raising valu1 to the valu2 power
  // until the power becomes one
  while (valu2 >= 1)
    {
    answ *= valu1;
    valu2--;
    }

  return(answ);
  } // end of exponent