macros in c

What is Macros in c?

In C programming language, a macro is a preprocessor directive that is used to define a symbolic name or a sequence of code that can be replaced with another sequence of code during the compilation process. Macros are defined using the #define directive and are typically used to simplify repetitive or complex code, to define constants, or to provide conditional compilation.

Micros are a small part of the program which is replaced  with another part of the preprocessor unit 

Macros is two type 

1. Predefined macros 
2. user-defined Macros(without arguments, with arguments)

Example of micros 

#include
#define PF printf
void main()
{
    PF("hello electro4u.net\n");
}

Output: hello electro4u.net

Attention: here we can define one macro PF with respect of printf, so that why we can use the PF as prinf for printing the output

Example: Program 2

#include<stdio.h>
#define int char
void main()
{
    int i;
    #undef int
    int j;
    printf("%ld\n",sizeof(i));
    printf("%ld\n",sizeof(j));
}

Note: micros name not should be constant 

What is the benefit of macros 

• Readability
• Replacement becomes easy

Predefined macros:

all the predefined macros start with a double underscore and end with a double underscore (_ _)

Program:

#include
void main()
{
    printf("%s\n",__FILE__);
    printf("%d\n",__LINE__);
    printf("%s\n",__DATE__);
    printf("%s\n",__TIME__);
}

Output:
5
Dec 28 2022
13:13:53

user-defined Macros(without arguments, with arguments)

Macro without Arguments:

This type of macro doesn't take any arguments and is simply a substitution of one string for another.

Example:

#define PI 3.14159

In this example, whenever the preprocessor encounters PI in the code, it will replace it with 3.14159.

Macro with Arguments:

This type of macro can accept one or more arguments and can perform operations on those arguments before substituting them into the code.

Example:

#define SQUARE(x) ((x) * (x))

In this example, SQUARE(x) is a macro that takes one argument (x) and returns the square of x.

Usage:

int result = SQUARE(5); // This will be replaced with: int result = ((5) * (5));

After preprocessing, this becomes:

int result = 25;

Note: Be cautious with macros that take arguments, as they can sometimes lead to unexpected behavior due to the way they are substituted in the code. For example, SQUARE(x++) would not behave as expected.