Basic ratio calculator for C64 implementation on C (cc65).

ratio_calculator.c

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <c64.h> 

unsigned char defaultBGColor = 0;
unsigned char defaultBorderColor = 0;
unsigned char defaultTextColor = 0;

void setUpScreen( void );
void resetDefaultScreen( void );
void usage( void );
void getArgs( int * n1, int * d1, int * n2, int * d2 );
char getAnswer( int n1, int d1, int n2, int d2 );

int main ( void )
{
   int n1 = 0;
   int d1 = 0;
   int n2 = 0;
   int d2 = 0;
   unsigned character = 0;
   int answer = 0;
   
   setUpScreen();

   usage();
   character = cgetc();
   
   while ( character != 'q' )
   {
      getArgs( &n1, &d1, &n2, &d2 );
      character = getAnswer( n1, d1, n2, d2 );
      
      clrscr();
   }

   resetDefaultScreen();
   
   return EXIT_SUCCESS;
}

void setUpScreen( void )
{
   clrscr();
   defaultBGColor = bgcolor( COLOR_BLACK );
   defaultBorderColor = bordercolor( COLOR_BLACK );
   defaultTextColor = textcolor( COLOR_GREEN );
}

void resetDefaultScreen( void )
{
   clrscr();
   bgcolor( defaultBGColor );
   bordercolor( defaultBorderColor );
   textcolor( defaultTextColor );
   * ( char *  ) 0xD018 = 0x15;
}

void usage( void )
{
   cputsxy( 12, 0, "RATIO CALCULATOR" );
   cputsxy( 12, 2, "N1/D1 = N2/D2" );
   gotoxy( 0, 4 );
   puts( "Input ratio pramams by prompt" );
   puts( "Press any key to continue" );
   puts( "or q to exit" );
}

void getArgs( int * n1, int * d1, int * n2, int * d2 )
{
   cursor( 1 );
   printf( "%s? ", "n1 (zero if unknown)" );
   scanf( "%d", n1 );
   printf( "%s? ", "d1 (zero if unknown)" );
   scanf( "%d", d1 );
   printf( "%s? ", "n2 (zero if unknown)" );
   scanf( "%d", n2 );
   printf( "%s? ", "d2 (zero if unknown)" );
   scanf( "%d", d2 );
   cursor( 0 );
}

char getAnswer( int n1, int d1, int n2, int d2 )
{
   int answer = 0;

   if ( n2 == 0 )
   {
      answer = d2 * n1 / d1;
      printf( "n2 = %d\n", answer );    
   }
   else if ( d2 == 0 )
   {
      answer = n2 * d1 / n1;
      printf( "d2 = %d\n", answer );    
   }
   else if ( n1 == 0 )
   {
      answer = d1 * n2 / d2;
      printf( "n1 = %d\n", answer );    
   }
   else if ( d1 == 0 )
   {
      answer = n1 * d2 / n2;
      printf( "d1 = %d\n", answer );    
   }
   else
   {
      puts( "Wrong params" );
   }
   
   puts( "Press any key to continue" );
   puts( "or q to exit" );
   
   return cgetc();
}