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I need to do modulo 256 arithmetic in C. So can I simply do
unsigned char i; i++; instead of
int i; i=(i+1)%256; 
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The modulo operator, denoted by %, is an arithmetic operator. The modulo division operator produces the remainder of an integer division. produces the remainder when x is divided by y.
(4) n ≡ 0 mod 2 if n is even, and n ≡ 1 mod 2 if n is odd. Modular arithmetic: The key fact about congruences is that congruences to the same modu- lus can be added, multiplied, and taken to a fixed positive integral power. For example, since 6 ≡ −1 mod 7, we have 61000 ≡ (−1)1000 = 1 mod 7.
Definition. Modular arithmetic is almost the same as the usual arithmetic of whole numbers. The main difference is that operations involve remainders after division by a specified number (the modulus) rather than the integers themselves.
An arithmetic overflow is the result of a calculation that exceeds the memory space designated to hold it. For example, a divide-by-zero yields a much larger result.
No. There is nothing that guarantees that unsigned char has eight bits. Use uint8_t from <stdint.h>, and you'll be perfectly fine. This requires an implementation which supports stdint.h: any C99 compliant compiler does, but older compilers may not provide it.
Note: unsigned arithmetic never overflows, and behaves as "modulo 2^n". Signed arithmetic overflows with undefined behavior.
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