Can't understand the result of one simple code

Question

Dear Members,

 

I am a fresh beginner in programming just started few days ago, I am totally new!

 

While studying one of the examples about the integers (byte and int) I can't understand why it gives this result:

 

here is the code:

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1. // Use byte.
2. using System;
3. class Use_byte {
4. static void Main() {
5. byte x;
6. int sum;
7. sum = 0;
8. for(x = 1; x <= 100; x++)
9. sum = sum + x;
10. Console.WriteLine("Summation of 100 is " + sum);
11. }
12. }

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the result is:

 

 Summition of 100 is 5050

 

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Can anyone please  explainstep by step why it shows 5050 and what is the logic of this code..

 

Thanks a lot.