The left-hand side of an assignment must be a variable, property or indexer
Assignment in conditional expression is always constant; did you mean to use == instead
The error mostly pops when a VB programmer codes in C#.
To fix this error, make sure that all operators are on the right-hand side and that the left-hand side is a variable, property, or indexer. Use == for checking values instead of ‘=’
if (String.IsNullOrEmpty(s1) == true)
if (String.IsNullOrEmpty(s1) = true)