Datatypes

Type of data which user wants to store in memory

Primitive / Predefined / Builtin

int

• negative numbers are stored in 2’s compliment notation.
• largest +ve number 32767 ($2^{15}-1$)
• for more we have to use modifiers
  • unsigned (without a sign bit)
    • $0$ to $2^{32}-1$ i.e $0$ to $65535$
  • long
    • 4 bytes are allocated. Range $2^{31}$ to $2^{31}-1$
  • short
    • smallest -ve number -32768 ($-2^{15}$)
    • Range $-32768$ to $32767$
• Generalize nbits $-2^{n-1}$ to $2^{n-1}-1$ ⭐ bound checking is not present in C

float

• used to define variables which can store real numbers
  • $m\ast b^e$
    • float x; 4 bytes of memory allocated for x.
    • Range $-3.4\ast 10^{38}$ to $3.4\ast 10^{38}$
    • no modifiers for float

double

• used to define variables which can store real numbers and its range is more than float
• double x; 8 bytes of memory allocated for x.
  • Range $-3.4\ast 10^{308}$ to $3.4\ast 10^{308}$
  • Only one modifier: Long.
    • 10 bytes of memory allocated
    • $-1.7\ast 10^{4932}$ to $17\ast 10^{4932}$

char

• used to define variables which can store character
• char x; only 1 byte of memory is allocated for x.
• $-2^7$ to $2^7-1$ => -128 to 127
• Only one modifier Unsigned. One byte memory
  • $0$ to $2^8-1$ => 0 to 255
• Character constant can initialize variable having char data
  • char x='a'; here a is a character constant
  • char x=a; here a is a variable
• Character constant can be single or double ch long. It can’t be of triple characters.

void

• non returnable functions & pointers

User defined

• structure
• union
• enum

char x = 97 // x = 9

char x = 'ab' // `x = 'a`