I did my homework and went to my grandmother's house. Before coordinating conjunctions we put a comma. Here we can omit the second subject. Do we need a comma before and or not?
NOT A TEACHER
(1) Teachers Fivejedjon and Mohammadhelmi have given us excellent answers.
(2) May I add a few comments, for I, too, am interested in your kind of question.
(3) When you get time, please study the differences between
simple sentences and
compound sentences.
(4)
I + did my homework and
went to my grandmother's house.
(a) One subject ("I") and two verbs for the one subject ("did" and "went"). So we
call that a simple sentence.
(b) In your sentence, you want to express the idea that "doing" and "going" were
equally important.
(5) Some people feel that it would be "better" to use two sentences connected with
"and" (a so-called compound sentence):
I did my homework +
I went to my grandmother's house.
That is, " I did my homework, and I went to my grandmother's house."
When you use two sentences, some people feel that you are more clearly
showing what happened after you did your homework.
NOTES:
(a) I agree that it is preferable to use a comma in that compound sentence.
But, as Teacher Fivejedjon taught us, it is not absolutely necessary.
(b) I wish to credit
Harper's English Grammar by John B. Opdycke, Ph.D., for the
semantic differences between simple and compound sentences.