[طائر الغربة]

Must / have to : they both mean s.th top necessary .generally they are interchangeable and the difference between them is too slight and just signify the degree of feeling : Must : personal feeling that s.th is necessary , Have to : s.one's else feeling
the Negative form of both is either : Needn't or Don't/ doesn't have to : they mean it isn't necessary to do s.th

Both of the following answers are correct :

No , you needn't

No, you don't have to.

Source : Macmillan: English for Palestine , grade 11
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User name : Tayer el-Ghurba
Real name : Shadi
Country : Palestine
City : Gaza