C Data Types & Constants | C Tutorial

As explained previously, a variable in C must be a specified data type, and you must use a format specifier inside the printf function to display the value present in the variable.

The data type specifies the size and type of information the variable will store.

Datatype

It is the type of value which the variable holds.

Here, we will focus on the most basic ones:

Data Type	Size	Description	Format Specifier
`int`	2 or 4 bytes	Stores whole numbers, without decimals	`%d` or `%i`
`float`	4 bytes	Stores fractional numbers, containing one or more decimals. Sufficient for storing 7 decimal digits	`%f`
`double`	8 bytes	Stores fractional numbers, containing one or more decimals. Sufficient for storing 15 decimal digits	`%lf`
`char`	1 byte	Stores a single character/letter/number, or ASCII values	`%c`

Below are some sub datatypes:

Data Type	Size	Description	Format Specifier
`short int`	2 bytes	Stores whole numbers, without decimals	`%hd`
`long int`	4 bytes	Stores whole numbers, without decimals	`%ld`
`unsigned short int`	2 bytes	Stores whole numbers, without decimals	`%hu`
`unsigned long int`	4 bytes	Stores whole numbers, without decimals	`%lu`

Here’s how we make use of the data type of a variable to print it.

#include <stdio.h>
 
int main()
{
    // Creating variables having different data types
    int integer = 26;
    float floating = 39.32;
    char character = 'A';
 
    // Printing variables with the help of their respective format specifiers
    printf("%d\n", integer);
    printf("%f\n", floating);
    printf("%c\n", character);
}

Output:

26
39.320000
A

C Constants

When you don't want the variables you declare to get modified intentionally or mistakenly in the later part of your program by you or others, you use the const keyword (this will declare the variable as "constant", which means unchangeable and read-only).
You should always declare the variable as constant when you have values that are unlikely to change, like any mathematical constant such as PI.
When you declare a constant variable, it must be assigned a value.

Here’s an example of how we declare a constant.

#include <stdio.h>
 
int main()
{
    const int MOD = 10000007;
}