Difference Between Typedef and Define in C with Example

In C, both #define and typedef are used for defining new names, but they serve different purposes and have some key differences.

#define:

Purpose:

• #define is a preprocessor directive used to create symbolic constants or macros.
• It doesn't create a new type; rather, it performs text substitution before the actual compilation process.

Example:

   #include <stdio.h>

   // Define a constant using #define
   #define PI 3.14159

   int main() {
       // Use the defined constant
       double radius = 5.0;
       double area = PI * radius * radius;

       printf("Area of the circle: %f\n", area);

       return 0;
   }

In this example, #define PI 3.14159 defines a macro PI that will be replaced with its value during preprocessing.

typedef:

Purpose:

• typedef is used to create new names for existing data types.
• It enhances code readability and can be especially useful when you want to create more descriptive names or abstract away implementation details.

Example:

   #include <stdio.h>

   // Define a typedef for int
   typedef int Age;

   int main() {
       // Use the typedef
       Age myAge = 25;

       // Print the age
       printf("My age is %d years.\n", myAge);

       return 0;
   }

In this example, typedef int Age; creates a new name (Age) for the existing data type int.

Differences:

• #define is a preprocessor directive that performs text substitution, whereas typedef creates an alias for an existing type, providing a new name for it.
• #define is not limited to type definitions; it is commonly used for defining constants and macros.
• typedef is specifically used for creating aliases for data types, improving code readability and maintainability.
• #define is processed by the preprocessor, and the substitution occurs before compilation, whereas typedef is part of the actual C code and is processed by the compiler.

In summary, #define is more versatile, used for defining constants and macros, while typedef is used for creating aliases for existing data types, making code more readable and maintainable.