I doubt whether/if he will come tomorrow.
Whether(If is uncorrect)he will come tomorrow is doubt ful.
It is doubtful whether/if he will come tomorrow.
I can't understand when I should use "whether"or "if".
Please help me🙇
The correct word is 'incorrect', not 'uncorrect'.
Whether denotes doubtfulness so they both need not be used in the same sentence.
I thing 'whether' would be かどうか ( he may or may not come). 'If' in this case would be もし (if he will come at all).