mssql which is the syntax 'if'

I have this code in mssql:

SELECT
    t1.Id,
    t2.Id,
    t1.QuantityIn,
    t1.PriceIn,
    t2.QuantityOut,

    (If (t2.QuantityOut - t1.QuantityIn)=0

        THEN t2.QuantityOut

    Else t2.QuantityOut - t1.QuantityIn ) AS Quant,

    t2.PriceOut

FROM t1

LEFT JOIN t2 ON t2.Id = t1.Id

In software MsSql Server Management Studio error is

Incorrect syntax near the keyword 'If'.

What is the correct syntax for 'if' in my case?

Thank you!