Surface Shader If Condition W = :( A == B ? V syntax

i found some strange syntax in a surface shader, but i can't find any documentation on what it is. can't i just write if... else in a void surf()? what is :(a==b ? syntax and where can i learn it? float4 resultCol1 = Alti >= _TopLimit ? tex2D(_TexTop, IN.uv_TexTop)