# High School Mathematics Extensions/Mathematical Programming/Exercise 1: Processing Commands

## Explanation

Includes

stdio.h
conio.h

Type Definitions

Values for TRUE and FALSE to get away from the standard C syntax of just testing for zero / not zero.

Function Prototypes

Prototype so we don't need to worry about forward references.

Global Variables

done = loop control in main.
r = denominator(on the right hand side of the operators).
l = numerator (on the left hand side of the operators).

Function Definitions init - set global variables.
input_message = prompt for a command.
retrieve_keypress = look for a keypress.
validate = make sure the command is one the program can handle.
execute_command = map the command on to the routines to implement it.
output_divide = implement divide '/'.
output_modulus = implement modulus '%'.
output_values = print out l and r.

## Code to change

Add and replace the following code:
```//includes
#include <stdio.h>
#include <conio.h>
//type definitions
#define TRUE 1
#define FALSE 0

//function prototypes
void init();
void input_message();
char input();
char retrieve_keypress();
char validate(char check_me);
void execute_command(char command);
void output_divide();
void output_modulus();
void output_values();
int get_integer();

//global variables
unsigned char done;
int r;
int l;

//function definitions
void init()
{
done=FALSE;
r=5;
l=2;
}
void input_message()
{
cprintf("Key      Action.\n");
cprintf("/        Display r/l = result.\n");
cprintf("%%        Display r%%l = result.\n");
cprintf("=        Display r=value, l=value.\n");
cprintf("r or R   Set the value for r.\n");
cprintf("l or L   Set the value for l.\n");
cprintf("x or X   End program.\n");
}
char input()
{
{
cprintf("\nInvalid Command.\n");
input_message();
}
}
int get_integer()
{
int ret_val;
char lastpress;

cprintf("Enter integer: ");
cscanf("%i",&ret_val);
lastpress=getch();
cprintf("\n");
return ret_val;
}
char retrieve_keypress()
{
char ret_val;
ret_val=getche();
cprintf("\n");
return ret_val;
}
char validate(char check_me)
{
char ret_val=0;
switch (check_me)
{
case '/':
case '%':
case '=':
case 'r':
case 'R':
case 'l':
case 'L':
case 'x':
case 'X':   ret_val++;
break;
}
return ret_val;
}
void execute_command(char command)
{
switch (command)
{
case '/':   output_divide();
break;
case '%':   output_modulus();
break;
case '=':   output_values();
break;
case 'r':
case 'R':   r=get_integer();
output_values();
break;
case 'l':
case 'L':   l=get_integer();
output_values();
break;
case 'x':
case 'X':   done++;
break;
}
}
void output_divide()
{
if (l > 0)
{
cprintf("%d / %d = %d.\n",r,l,r/l);
}
else
{
cprintf("r = %d, l = %d. Please set l to a value other than 0.\n",r,l);
}
}
void output_modulus()
{
if (l > 0)
{
cprintf("%d %% %d = %d.\n",r,l,r%l);
}
else
{
cprintf("r = %d, l = %d. Please set l to a value other than 0.\n",r,l);
}
}
void output_values()
{
cprintf("r = %d, l = %d.\n",r,l);
}
void main()
{
char command;
init();
input_message();
while(!done)
{
command=input();
execute_command(command);
}
}

```