Constants in C Programming Language

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Constants in C :

A constant stores a value that cannot be changed from its initial assignment.
By using constants with meaningful names, code is easier to read and understand.
To distinguish constants from variables, a common practice is to use uppercase identifiers.

One way to define a constant is by using the const keyword in a variable declaration:

#include <stdio.h>
int main() {
    const double PI = 3.14;
    printf("%f", PI);
    return 0;
}


The value of PI cannot be changed during program execution.

For example, another assignment statement, such as PI = 3.141 will generate an error.
Another way to define a constant is with the #define preprocessor directive.
The #define directive uses macros for defining constant values.
For example:

#include <stdio.h>
#define PI 3.14
int main() {
    printf("%f", PI);
    return 0;
}

Before compilation, the preprocessor replaces every macro identifier in the code with its corresponding value from the directive. In this case, every occurrence of PI is replaced with 3.14.
The final code sent to the compiler will already have the constant values in place.

The difference between const and #define is that the former uses memory for storage and the latter does not.

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