FOR

for variable=start, stop, [count_by] do
	--code to repeat
end

"For loops" begin counting from the "start" number, count up or down by the "count by" number, and stops after reaching the "stop" number.

A "for loop" is a programming structure that allows you to repeat a set of instructions multiple times. It's like a machine that can do the same task over and over again. You tell the machines how many times to repeat the actions it is meant to do, and it does the rest. It's very useful for doing repetitive tasks quickly and efficiently.

Examples:

for i=1, 9, 2 do
	print( i )
end

--prints: 1 3 5 7 9

If the "count by" number is left out, then it will automatically be 1.

for i=1, 9 do
	print( i )
end

--prints: 1 2 3 4 5 6 7 8 9

If you want to count down, then make the "count by" number a negative number.

for i=10, 3, -1 do
	print( i )
end

--prints: 10 9 8 7 6 5 4 3

It's important to note that the index number is not checked until the end of each loop, so even when the "start" and "stop" numbers are the same, the loop will still run once through.

for i=0, 0 do
	print( i )
end

--prints: 0

You may come across or need to use a double loop, or a loop within a loop. These are called "nested loops". Here is an example:

for i=0, 3 do
	for j=1, 2 do
		print( j )
	end
	print( "i="..i )
end

--prints: 1 2 i=0 1 2 i=1 1 2 i=2 1 2 i=3

You can differentiate the two loops by saying "outer" and "inner" loop. Just as it is common to use i as the index variable name, it is also common to then use the next letters, j, k, etc. for each inner loop. Notice that the index number of i doesn't change until j has printed itself twice.