Why stores 255 in a char variable give its value -1 in C?

Question

I am reading a C book, and there is a text the author mentioned:

\"if ch (a char variable) is a signed type, then storing 255 in the ch variable gives it the

Answer 1

You have classical explanation in others messages. I give you a rule:

In a signed type with size n, presence of MSB set as 1, must interpreted as -2^(n-1).

For this concrete question, assuming size of char is 8 bits length (1 bytes), 255 to binary is equal to:

1*2^(7) +  
1*2^(6) + 
1*2^(5) + 
1*2^(4) + 
1*2^(3) + 
1*2^(2) + 
1*2^(1) + 
1*2^(0) = 255

255 equivalent to 1 1 1 1 1 1 1 1.

For unsigned char, you get 255, but if you are dealing with char (same as signed char), MSB represents a negative magnitude:

-1*2^(7) +  
1*2^(6) + 
1*2^(5) + 
1*2^(4) + 
1*2^(3) + 
1*2^(2) + 
1*2^(1) + 
1*2^(0) = -1