if statement - how does IF affect complexity?

Question

Let's say we have an array of 1.000.000 elements and we go through all of them to check something simple, for example if the first character is "A". From my (very little) understanding, the complexity will be O(n) and it will take some X amount of time. If I add another IF (not else if) to check, let's say, if the last character is "G", how will it change complexity? Will it double the complexity and time? Like O(2n) and 2X?

I would like to avoid taking into consideration the number of calculations different commands have to make. For example, I understand that Len() requires more calculations to give us the result than a simple char comparison does, but let's say that the commands used in the IFs will have (almost) the same amount of complexity.

Answer 1

O(2n) = O(n). Generalizing, O(kn) = O(n), with k being a constant. Sure, with two IFs it might take twice the time, but execution time will still be a linear function of input size.

Edit: Here is an explanation, with examples, of the big-O notation which is not too mathematic-oriented