1. If anyone doesn't find me, I will die.

2. If no one finds me, I will die.

(Are both grammatical?)

3. You have to practice playing the piano.

4. You have to practice to play the piano.

5. You have to practice the piano.

(Which ones are correct from #3 to #5?)

#2 is correct. You can change #1 to read - If someone doesn't find me, I will die.

3-5 are all correct.

1. Yes, the sentence "If anyone doesn't find me, I will die" is grammatically correct. It uses the conditional structure "If... then" to express a hypothetical situation and the consequence that follows.

2. No, the sentence "If no one finds me, I will die" is not grammatically incorrect, but it sounds less natural compared to the first sentence. Using "no one" instead of "anyone" gives it a slightly different meaning and may be less commonly used.

3. The sentence "You have to practice playing the piano" is correct. It expresses the necessity or requirement of practicing the act of playing the piano.

4. The sentence "You have to practice to play the piano" is not grammatically correct. The verb "practice" should be followed by a noun or a gerund form of a verb (ending in -ing), not an infinitive (in this case, "to play").

5. The sentence "You have to practice the piano" is correct. It implies that you need to practice the specific instrument, the piano, without mentioning the act of playing explicitly.

1. "If anyone doesn't find me, I will die." - This sentence is grammatically correct. It implies that if nobody finds the speaker, they will die.

2. "If no one finds me, I will die." - This sentence is also grammatically correct. It has the same meaning as the previous sentence, using a slightly different wording by replacing "anyone" with "no one."

3. "You have to practice playing the piano." - This sentence is correct. It suggests that in order to improve your piano skills, you need to practice playing the piano.

4. "You have to practice to play the piano." - This sentence is grammatically incorrect. The correct form should be "You have to practice in order to play the piano." This sentence conveys that practicing is necessary to achieve the ability to play the piano.

5. "You have to practice the piano." - This sentence is grammatically correct. It implies that you need to engage in regular practice sessions specifically focused on the piano in order to improve your skills.