C Basic Types

Integer Types

Integers can be signed & unisgned
By default they are signed
In a signed integer the left-most bit is set to 0 when number is positive or 0

Largest signed 16-bit number: $2^{15}-1=32,767$
Largest unsigned 16-bit number: $2^{16}-1=65,535$

Integer Sizes: short int, int, long int
Order of specifiers don’t matter: unsigned long int same as long unsigned int
Word int can be omitted when long or short are used

int is normally 32-bits long but can be 16-bits on older CPUs
<limits.h> can be referenced to find the macro that defines the upper and lower bounds

C99
New integer: long long int
Has to be at minimum 64-bit long
Supports implementation defined extended integers (Compiler could add 128-bit integer)

Type	Datatypes
Standard Signed Integers	short int, int, long int, long long int, signed char
Standard Unsigned Integers	unsigned short int, unsigned int, unsigned long int, unsigned long long int, unsigned char, _Bool

Integer Constants

Constants can be represented in decimal, Octal or Hexadecimal
Decimal cannot start with 0
Octal starts with 0
Hex starts with 0x
Add 3 types can be mixed together in a expression

For decimal constants storage the compiler will use the following order:
int → long int → unsigned long int
For octal and hexadecimal constant storage the compiler will use the following order:
int → unsigned int → long int → unsigned long int

To force it to be treated as long int we can use L
To force it to treated as unsigned we can use U

C99
For decimal constants storage the compiler will use the following order:
int → long int → long long int
For octal and hexadecimal constant storage the compiler will use the following order:
int → unsigned int → long int → unsigned long int → long long int → unsigned long long int

To force it to be treated as long long int we can use LL

Integer Overflow
Signed Integer overflow result undefined
Unsigned Integer overflow will cause the number to wrap-around

Type	Datatype	Format Specifier
Signed Integer	int	%d
Unsigned Integer (Decimal)	unsigned int	%u
Unsigned Integer (Octal)	unsigned int	%o
Unsigned Integer (Hexadecimal)	unsigned int	%x
Signed Short	short	%hd
Unsigned Short (Decimal)	unsigned short	%hu
Signed Long Int	long int	%ld
Unsigned Long Int (Decimal)	unsigned long int	%lu
Signed Long Long Int	long long int	%lld
Unsigned Long Long Int (Decimal)	unsigned long long int	%llu

IMPORTANT

We cannot print signed hexadecimal and octal numbers
For negative numbers printf will consider the 1 in the MSB to be part of the number itself causing a vary large number to be printed

Floating Types

Types: float, double, long double
Use float when precision is not important. Long Double provides the most precision
IEEE Standard 754: Floating Point Number Representation

float: Single Precision (binary32), double: Double Prevision (binary64)
Implementation of long double is dependent on the compiler and system

C99
Real Types: Types: float, double, long double
Complex Types: float _Complex, double _Complex, long double _Complex

Floating Constants

Float constants are stored by default as double
To force it to be float use F for long double we use L
For scientific notation e is used to denote the exponent (5.7e1)

Type	Reading	Printing
Float	%f, %e, %g	%f, %e, %g
Double	%lf, %le, %lg	%f, %e, %g
Long Double	%Lf, %Le, %Lg	%f, %e, %g

C99
Hexadecimal floats use p to represent the exponent
The exponent is denoted in decimal even though its an power of 2
e.g. 0x1.Bp3 = $1.6875\times 2^3$ = 13.5 (Decimal)
B is represented in binary before its binary value is calculated

Character Types

The char type in C is essentially a integer type

Integer values can be stored in char datatype
The character corresponding to the code point will be displayed when printed
The character displayed can be different based on character set used by the system

char ch;
int i;
 
i = 'a';        /* i is now 97 */
ch = 65;        /* ch is now 'A' */
ch = ch + 1;    /* ch is now 'B' */
ch++;           /* ch is now 'C' */

Comparison operations can be used on char just like an int
The integer value of the character is used for the comparison

if ('a' <= ch && ch <= 'z') {
	ch = ch - 'a' + 'A';
}

char can be signed (-128 to 127) or unsigned (0 to 255)
C does not enforce the type for ordinary char
Compiler can implement ordinary char as signed or unsigned
Use the signed and unsigned keywords to enforce the required type

scanf does not skip white-space when reading characters

/* skips white space, then reads ch */
scanf(" %c", &ch);

getchar() and putchar() are character specific scanf and printf

0 in ASCII represents NULL (Useful for initializing character arrays)

Escape Sequence

\xHH: Hexadecimal Escape Characters
\OO: Octal Escape Characters

#include <stdio.h>
 
int main() {
    printf("Hello,\\nWorld!");                // Hello,\nWorld!
    printf("\x48\x65\x6C\x6C\x6F");           // Hello
    return 0;
}

Type Conversion

Implicit Conversion

Operands in a expression don’t have the same type (Usual Arithmetic Conversion)
Type of expression on right cannot be assigned to type of expression on left
Type of argument in function does not match type of parameter
Type of expression in return statement does not match functions return type

Converted to narrowest type that can accommodate both the values
A type is said to be narrower than another if it requires fewer bytes
The narrower type is converted to the type of the other operand (Promotion)
Integers are promoted to a unsigned type before promoting to a bigger size

When signed operand is combined with an unsigned operand the result is unsigned
The conversion is performed by adding or subtracting a multiple of MAX + 1

Explicit Conversion

cast is considered to as a unary operator
Has higher precedence than binary operators

INFO

If we assign an larger int to an smaller unsinged int the extra bits are discarded
If the variable is signed type then the result is implementation dependent
If a large float is stored into a integer type or smaller float type the result is undefined behavior

Type Definitions

Used to create custom datatypes
By convention the 1st letter of the name should be capital

typedef int Bool;
Bool flag;              /* same as int flag; */

C99
The header <stdint.h> contains definitions for integers of fixed sizes
There is no float equivalent so floats processions and range can vary by platform

sizeof Operator

Returns the memory in bytes required to store a datatype
Returns a value of type size_t which is always an unsigned integer type

sizeof is an unary operator and has higher precedence than binary operators
It can be used without the parenthesis but precedence can cause problems when used to find the size of an expression

C89: Result of sizeof should be cast to unsigned long (largest int type)
C99: The value is automatically cast by printf if z is added before the unsigned int format specifier

printf("Size of int: %lu\n", (unsigned long) sizeof(int));
printf("Size of int: %zu\n", sizeof(int)); /* C99 only */