while loop in C# with multiple conditions

Question

This is my code:

while( Func(x) != ERR_D)
{
   if(result == ERR_A) 
         throw...; 
   if(result == ERR_B)
         throw...;

  mydata.x = x;
 }

The problem is that I want to use result = Func(x) in the while condition as the result will be checked inside the while loop. The while loop should call Func(x) untill it returns ERR_D. I can't use

do{ 
    result = Func(x);
   if(result == ERR_A) 
         throw ...; 
   if(result == ERR_B)
         throw ...;
    mydata.x = x;
   }while(result != ERR_D); 

in my project as it first calls Func(x) which is what I don't want. But I have tried while(result = Func(x) != ERR_D), it doesn't work. Any ideas to solve this?

Answer 1

You just need to add some parentheses:

while((result = Func(x)) != ERR_D) { /* ... */ }

The != operator has a higher priority than the assignment, so you need to force the compiler to perform the assignment first (which evaluates to the assigned value in C#), before comparing the values on both sides of the != operator with each other. That's a pattern you see quite often, for example to read a file:

string line;

while ((line = streamReader.ReadLine()) != null) { /* ... */ }