Question

how many avatar vishnu have and .. avatar names one by one

Answer 1

Technically, there are uncountable incarnations of Lord Vishnu.

Officially there are 10 incarnations.

MatsyaKurmaVarahaNarasimhaVamanaParashuramRamKrishnaGautama Buddha (now please don't start a debate, I wrote his name because I had read bhagavat purana, it was written by ved vyasa, he clearly mentioned Gautama Buddha as an avatar of Vishnu)Kalki

Note - don't come with a stupid logic like Balarama was a avatar of Vishnu. He was avatar of Sheshnag, who in turn was ansh of Vishnu.

Answer 2

total 10 avtar he had : .
1. matsya
2.kurma
3. varaha
4. narasimha
5. vamana
6. parasurama
7. lord rama
8. lord krishna
9. balarama
10. kalki

hope this answer will help u