Very simple stuff, have no clue. Topic is solved

[GammaSerpentisFTW]

In short:

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if year > oldyear
	msgbox yay

year = 2134
oldyear = 0
No msgbox, but if I change it to:

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if year > 0
	msgbox yay

Got msgbox with "yay"

What am I missing here?
Full code:

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string = "year: 2134 month: 11"
oldyear := 0
string := SubStr(string, InStr(string, "year: ") + 6) ; =2134 month: 11"

year := SubStr(string, 1, 1)
j := 2
Loop
	{
	If Not (SubStr(string, j, 1) = " ")
		{
		year := year . SubStr(string, j, 1)
		j++
		}
	Else Break
	}
if year > oldyear
	msgbox yay

[jeeswg]

It's always best to use parentheses. Regarding the results below, I didn't actually know the exact results until I tested. When you omit parentheses, it uses the legacy style syntax. Cheers.

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q:: ;test a = b and (a = b)
var1 := 10
var2 := 10

if 10 = var2
	MsgBox, 1
if 10 = %var2%
	MsgBox, 2
if (10 = var2)
	MsgBox, 3 ;works (recommended)
if (10 = %var2%)
	MsgBox, 4

if var1 = var2
	MsgBox, 5
if var1 = %var2%
	MsgBox, 6 ;works (legacy style)
if (var1 = var2)
	MsgBox, 7 ;works (recommended)
if (var1 = %var2%)
	MsgBox, 8

if 10 = var2
	MsgBox, 9
if 10 = %var2%
	MsgBox, 10
if (10 = var2)
	MsgBox, 11 ;works
if (10 = %var2%)
	MsgBox, 12

if 10 = 10
	MsgBox, 13
if 10 = %10%
	MsgBox, 14 ;'works' (but it is not comparing 10 with 10: it is getting the contents of a variable called 10 in each example, the variable '10' is not defined, so it is comparing a blank string with a blank string)
if (10 = 10)
	MsgBox, 15 ;works
if (10 = %10%)
	MsgBox, 16
return

[EDIT:] Added 8 more MsgBox tests above.

[GammaSerpentisFTW]

Thank you, jeeswg! It works, I will use parentheses from now on.

[jeeswg]

Btw when using functions or multiple parentheses, I believe the following lines in each pair are equivalent. I.e. there are some occasions when you can omit parentheses.

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if InStr(vText, vNeedle)
if (InStr(vText, vNeedle))

if vPos := InStr(vText, vNeedle)
if (vPos := InStr(vText, vNeedle))

if (a = b) && (c = d)
if ((a = b) && (c = d))

[Osprey]

You could've also solved it by adding % signs on either side of "oldyear":

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if year > %oldyear%
	msgbox yay

When using such legacy (non-parenthetical) syntax, you need the % signs around variables that are on the right side of assignments and comparisons. When you use parentheses, you don't need them, since parentheses tell AHK to use expression syntax. In expression syntax, everything is assumed to be a variable (or object) unless it has quotes around it, whereas, in legacy syntax, everything on the right of assignments and comparisons is considered to be an unquoted string unless there are % signs (i.e. in your original code, variable "year" was being compared to the 7-character string "oldyear", not the variable of the same name). In general, it's better to use the newer, parenthetical syntax, but you can't totally get away from legacy syntax, since many commands, like MsgBox, use it. It's one of the few annoying things about AHK.