/*
	An important requirement of any program will be to make decisions on various things such as user input, 
	collisions between sprites, checking if the player has run out of lives and so on.
	
	This tutorial introduces the IF - THEN - ELSE structure that can be used to test if conditions are true.
	
	We have already been introduced to a conditional test with the while loop in the previous tutorial.  Theere we
	tested:  index < 40  - what we are saying here is while index is less than 40, do the loop.
	
	The following can be used when testing a condition:
	
	= 		example: a = 3		Means if a equals 3 then the condition is true (note this is different to assignment := )
	>		example: a > 3		Means if a is greater than 3 then the condition is true
	<		example: a < 3		Means if a is less than 3 then the condition is true
	>=		example: a >= 3		Means if a is greater than or equal to 3 then the condition is true
	<=		example: a <= 3		Means if a is less than or equal to 3 then the condition is true
	<>		example: a <> 3		Means if a is not equal to 3 then the condition to true
	
*/
program IfThenElse;
var  
	val1, val2: byte; 	// Define two variables
   
begin
	// define the screenmemory pointer
	definescreen();
	
	// clear the screen and colour memory
	clearscreen(32, screen_char_loc);
	clearscreen(WHITE, screen_col_loc);
	
	// Set the screenmemory pointer to point to the screen memory:
	screenmemory := screen_char_loc;

	// lets set the val1 and val2 variables to some values we can test with:
	val1 := 10;
	val2 := 20;
	
	// The most simple IF statement can look like the following:
	if (val1 = 10) then printstring("VAL1 IS EQUAL TO 10",0,40);
	// IF begins the condition test, we then ask if val1 = 10, and if true, THEN execute the PrintString command and that's it.
	
	screenmemory := screenmemory + screen_width;	// move to next line on the screen
	
	// An IF statement can also have an ELSE.  Where THEN is executed if the condition is true, the ELSE is executed if it is not
	// when using ELSE, must put code into blocks marked with a begin and end 
	if (val1 = 20) then
	begin		// this will be executed if the condition is true
		printstring("VAL1 IS EQUAL TO 20",0,40);
	end			// note this end does not have a semi-colon ; character
	else
	begin		// this will be executed if the condition is not true
		printstring("VAL1 IS NOT EQUAL TO 20",0,40);
	end;		// but this one does because it marks the end of this structure

	screenmemory := screenmemory + screen_width;	// move to next line on the scree

	// Can test two variables in a condition
	if (val1 >= val2) then
	begin
		printstring("VAL1 IS GREATER OR EQUAL TO VAL2",0,40);
	end
	else
	begin
		printstring("VAL1 IS NOT GREATER OR EQUAL TO VAL2",0,40);
	end;

	screenmemory := screenmemory + screen_width;	// move to next line on the screen

	// Now lets combine a FOR loop and an IF statement
	// val1 will count from 15 to 25
	for val1 := 15 to 26 do
	begin
		// display the values of val1 and val2 side by side on the screen
		printdecimal(val1,1);
		screenmemory := screenmemory + 3;
		printdecimal(val2,1);
		screenmemory := screenmemory + 3;
		// now lets do three conditions and print a string when any are true
		if (val1 < val2) then printstring("VAL1 IS LESS THAN VAL2",0,40);
		if (val1 = val2) then printstring("VAL1 IS EQUAL TO VAL2",0,40);
		if (val1 > val2) then printstring("VAL1 IS GREATER THAN VAL2",0,40);
		screenmemory := screenmemory + screen_width - 6;	// move to next line on the screen
	end;

	loop();
end.
