Question

Why my C# code returns 0, if it must be 50 ?

double c = (1 / 2) * 100;
Console.WriteLine(c); 

what is wrong?

Answer 1

1, 2 and 100, in your example, are all int literals. In C#, integer division returns integers, and ignores the remainder. Only after calculating 1/2 (=0) and multiplying by 100 (=0) does the result get converted to double

(1.0/2) * 100

Would give the expected result, because now 1.0 is a double literal, and forces the other literals to be converted to doubles also before the calculations are performed.