Digital Computers

Binary

Characteristics

• Only consists of 1 and 2.

• Most significant bit (MSB) is on left.

• 1 byte = 8 bits

Machine code (Assembly) Instruction Set

1. Data Transfer (read and write memory)

2. Data Manipulation (change memory)

3. Program Flow (change next execution)

Programming Language: C

Variables & Types

Variable is text names for addresses in memory. Type is organization and size of memory. Below are some examples of the space occupied by different types in C.

Type	Spaec occupied
char	8 bits
int	16 bits
unsigned long	32 bits
float	32 bits

Note that int type is signed in C!!! So, if we try to assign 32768 to an int variable, the variable will store -32768 instead.

In C, signed type using 2's complement form to store the numbers. So, even if two types use the same number of bits, the number range they represent are different.

unsigned vs signed

In the example below, since char is a signed type and it is 8 bits long. If we assign 128 to it, in binary, it will be 10000000. As we have discussed before, signed type means it will use 2's complement form to store its number. In 2's complement representation, 10000000 is -128. So, the value in f will be -128.

int e = 128;
char f = e; // f = -128

Operators

The following table contains operators that manipulate one or two numbers

Operator name	Operator
Arithmetic	+ - * /
Comparison	== != < <= > >=
Logic	! && ||
Bitwise (Do the evaluation on each bit)	& | ^ ~ >> <<

~ represents bitwise not.

Tips

1. Include the ASCII code list in the cheatsheet!