Changing states on the change of a counter variable

I have kept a counter on the click of a title. I'm trying to change the state of the title when the counter variable contains an even number. I have created a variable named "counter" whose default value is 0 and this works till the counter variable increments to 2.

But it should be in the following way; 

Counter = 1(odd),  no change in the state

Counter = 2(even), change in the state

Counter = 3(odd), no change in the state

Counter =4(even), change in the state and so on

 

Could someone please suggest me a way to do this?

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