/* tinycal.c		*/
/* a tiny calculator	*/
/* Author: Weiwei Chen	*/
/* Date: Oct. 31. 2010	*/

/*preprocessor directives*/
#include <stdio.h>

/*global variables*/
int i1, i2, res, compokey;

/*function declaration */
void add(int op1, int op2);
void sub(int op1, int op2);
void mul(int op1, int op2);
void div(int op1, int op2);
void printMenu();
void getInput();
void outputResult(int n);

/*main function*/
int main(void)
{
	/*variable definitions*/
	int choice = 0;

	/*input, computation and output sections*/
	do
	{
		printMenu();
		scanf("%d", &choice);
		switch(choice)
		{
		case 1: getInput();
			add(i1, i2);
			outputResult(res);
			break;

		case 2: getInput();
			sub(i1, i2);
			outputResult(res);
			break;
 
		case 3: getInput();
			mul(i1, i2);
			outputResult(res);
			break;
 
		case 4: getInput();
			div(i1, i2);
			if(compokey){
				outputResult(res);
			} 
			break;

		default: break; 
		}
	}while(choice != 0);

	return 0;
}


void add(int op1, int op2)	/*addition of two numbers*/
{
	res = op1 + op2;
}

void sub(int op1, int op2)
{
	res = op1 - op2;
}

void mul(int op1, int op2)
{
	res = op1 * op2;
}

void div(int op1, int op2)
{
	compokey = 1;
	if(op2 == 0)
	{
		printf("   	invalid divisor 0!!!! \n");
		printf("********************************\n\n");
		compokey = 0;
		return;
	}
	res = op1 / op2;
}

void printMenu()
{
	printf("   1. add two numbers \n");
	printf("   2. subtract two numbers \n");
	printf("   3. multiple two numbers \n");
	printf("   4. divide two numbers \n");
	printf("   0. exit \n");
	printf("   Enter your choice: ");
}
void getInput()
{
	printf("   	i1 = ");
	scanf("%d", &i1);

	printf("   	i2 = ");
	scanf("%d", &i2);
}

void outputResult(int n)
{
	printf("   	The result is %d \n", n);
	printf("********************************\n\n");
}