[Grammar] Present perfect and past simple

[Dzidzi]

Which tense do i use in these sentences :

I decided to start doing exercises every day.
I have decided to start doing exercises every day.

I always wanted to play piano.
I have always wanted to play piano.

 

[jutfrank]

Which one you use depends on what you mean to communicate.

I have decided to start doing exercises every day.

This sentence tells me about something new in your life that you want to try. You are thinking of your future action. You probably have not started doing the exercises yet.

I decided to start doing exercises every day.

You are telling me about a decision you made last year, or at some other time in the past. Maybe this sentence is part of a story about your life.

 

[Dzidzi]

Are both sentences correct ?

I haven't been a good friens to you .
I wasn't a good friend to you .

 

[tzfujimino]

Are both sentences correct?

I haven't been a good friend to you.
I wasn't a good friend to you.

Yes, they are grammatically correct.

 

[Dzidzi]

Is there any difference in meaning ?

 

[GoesStation]

I haven't been a good friend to you: from some time in the past until now, my friendship towards you has been inadequate.

I wasn't a good friend to you: during a period of time in the past, I was not a good friend to you.

 

[emsr2d2]

Is there any difference in meaning?

Don't put a space before a question mark.

 

[Dzidzi]

Now I will tell you something you might not have known about me.
Now I will tell you something you might didn't know about me.

Which one is correct and is there any difference in meaning

 

[GoesStation]

Only the first is correct. Modal verbs are followed by a bare infinitive, not a conjugated verb.

 

[Dzidzi]

How should i say?

I made a huge mistake .
I have made a huge mistake .

 

[emsr2d2]

How should I say the following?

I made a huge mistake.
I have made a huge mistake.

Both of your sentences are grammatically correct. They are used in different situations. Do you understand when we use the past simple (made) and when we use the present perfect (have made)?

Note that "How should I say?" is not a complete sentence. Also, don't put a space before a full stop.