Data Types

Primary Data Types

In C, there are 5 primary data types:

int
float
double
char
void: if a function is not returning anything, its return type should be void. Note that, you cannot create variables of void type.

Other types are derived from these ones (array,structure,etc.)

Size and modifiers

Bytes reserved in the memory can change according to the computer, but the sizeof() operator can be used to check
Normally:
- int : 4
- char: 1
- float: 4
- double: 8
short and long modifiers can be used before the type to limit (or expand the size) (Even long long is valid)
signed and unsigned can be used to change the range.

For example:

#include<stdio.h>
int main(int argc, char const *argv[])
{
    printf("int:%d\n",sizeof(int));
    printf("short int:%d\n",sizeof(short));
    printf("long int:%d\n",sizeof(long));
    printf("char:%d\n",sizeof(char));
    printf("float:%d\n",sizeof(float));
    printf("double:%d\n",sizeof(double));
    return 0;
}

Outputs:

int:4
short int:2
long int:4
char:1
float:4
double:8

In the case of integers, the stdint.h header file defines types and constant to work with precisely specifed types (Like uint64_t which represents an unsigned integer which is always 64 bits). More information here.

Constants

Constant Data type

-Declared just like a normal variable, using the keyword const

Value has to be assigned when created
Has limited scope (to where is defined)

int main()
{
    const int x = 5;
    //Scope valid in the main method
}

Constant Expression

Creates constants in the preprocessor (directive)
Using the directive #define followed by an immediate value to assign
Name in ALL CAPS
No semicolon
Scope throughout the whole file when defined

#define ROWS 20
#define COLUMNS 60
#define GRID ROWS*COLUMNS //Scope in whole file

int main() {
    //something
}

Boolean Values

C has no boolean primitive types, however it uses the convention that 0 means “false” and any non-zero value means “true.” Boolean variables and functions that return Boolean values are traditionally declared int. The stdbool.h library provides support for more explicit booleans in modern C compilers. For example:

#include <stdio.h>
#include <stdbool.h>

int main(void) {
    bool x = true;  /* equivalent to bool x = 1; */
    bool y = false; /* equivalent to bool y = 0; */
    if (x)  /* Functionally equivalent to if (x != 0) or if (x != false) */
    {
        puts("This will print!");
    }
    if (!y) /* Functionally equivalent to if (y == 0) or if (y == false) */
    {
        puts("This will also print!");
    }
}