Problem with decreasing a variable

[darton]

Hello!
In one of my scripts there is this line:

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incr i [lindex $line 0]

But now I don't want to increase it but I want to decrease it. So I changed it to this:

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incr i [lindex $line 0] -1

It does not work. The error is: Tcl error [flag]: wrong # args: should be "incr varName ?increment?"
What's wrong?

[Garp]

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incr i [lindex $line 0] -1

you do something like "1 +1 -1" but incr allows only one operation like "1+1" or "1-1"

(($i + $y) - $z) it would be something like

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set i [expr [incr i [lindex $line 0]] -1]

[DragnLord]

simply:

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incr i -1

in the script you have '[lindex $line 0]' is used to obtain the increment value

[darton]

With the '[lindex $line 0]' it is defined what should be increased. So none of your scripts work.

[Sir_Fz]

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incr i -[lindex $line 0]

this will decrement i by '[lindex $line 0]' instead of increment.

[darton]

Yes, it works Sir_Fz. But if i is 3 and it should be decreased the result is 2. With your script it is not 2, but -2. With "trimleft" I can make the variable i positive again, but maybe this is too circumstantial and there is an easier way.

[DragnLord]

if

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[lindex $line 0]

is "2"

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incr i -[lindex $line 0]

means that it is increased by -2, which means it is decreased by 2
obviously you didn't bother to try it[/code]

[phab]

Doenst

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set i [expr {$i - [lindex $line 0]}]

work?

[De Kus]

its equivalent with 'incr i -[lindex $line 0]', however only the expr one will work on negative values.