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.
input = read command.
get_integer = read an integer.
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()
 {
     char read;
     read=retrieve_keypress();
     while (!validate(read))
        {
            cprintf("\nInvalid Command.\n");
            input_message();
            read=retrieve_keypress();
        }
     return read;
 }
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);
       }
 }

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