08 Variables in C++

1. Variable Types

In C++, the only difference between different variable types is their size, i.e., how much memory the variable occupies.

The actual size of a data type depends on the compiler, and it may vary due to different compilers.

1.1 int

The int type is designed to store integers within a certain range, as it has a size of 4 bytes.

\(1byte=8bits,4bytes=32bits\)

Variables are signed, meaning one bit is used to represent the sign (\(\pm\)), leaving only 31 bits for the actual number representation. 1 bit can be either "0" or "1", \(2^{31}=2,147,483,648\) (over 2.1 billion). Since 0 also needs to be represented, the maximum number that can be represented is \(2^{31}-1\).

\(\therefore\) The range of int is \((-2147483648 , 2147483647)\).

What if I only want positive numbers?

\(\ce { -> }\) Use an unsigned number, which can represent \(2^{32}\) ^7a7e3b

unsigned int

1.2 Common Types

char	short	int	long	long long	(long int)
1 byte	2 bytes	4 bytes	4 bytes	8 bytes	4 bytes

Any type can be prefixed with unsigned.

1.3 char

Making assumptions about certain data types.

char a = 'A';  // A

char a = 65;   //  A

Because when a char is passed to std::cout, it is treated as a character rather than a number.

short a = 65;  // 65

short a = 'A'; // 65

1.4 Storing Decimal Numbers

float & double

float occupies 4 bytes and is distinguished from double by appending "F/f" to the number. double occupies 8 bytes.

1.5 bool

0 for false anything except 0 for true

Occupies 1 byte.

Since memory addressing cannot directly access bits but only bytes, you can cleverly store 8 bools in one byte to save memory.

2. sizeof Operator

std::cout << sizeof(bool) << std::endl;   // 1

3. Pointers & References

Pointers: type* bool*

References: type& bool&