typedef Keyword in C

What is typedef?

The typedef keyword allows you to assign a custom name to any datatype (built-in, struct, pointer, array, etc.).

• Makes complex declarations easy to read
• Useful in structures, pointers, arrays
• Reduces confusion in large programs
• Common in industry-level C programming

Basic Syntax

typedef existing_type new_name;

typedef int Marks;
Marks m1 = 80;

Why Use typedef?

• Simplifies complex types (pointers, structures, function pointers)
• Improves readability and maintenance
• Makes code look like high-level languages
• Used heavily in embedded systems and OS code

Examples of typedef

1. typedef for int

#include <stdio.h>

typedef int Number;

int main() {
    Number a = 10;
    printf("%d", a);
    return 0;
}

2. typedef for float

#include <stdio.h>

typedef float Price;

int main() {
    Price p = 99.75;
    printf("%.2f", p);
    return 0;
}

3. typedef for a pointer

#include <stdio.h>

typedef int* IntPtr;

int main() {
    int a = 10;
    IntPtr p = &a;
    printf("%d", *p);
    return 0;
}

4. typedef for array

#include <stdio.h>

typedef int Marks[5];

int main() {
    Marks m = {10,20,30,40,50};
    printf("%d", m[2]);
    return 0;
}

5. typedef with struct

#include <stdio.h>

typedef struct {
    int roll;
    char name[20];
} Student;

int main() {
    Student s = {1, "Sourav"};
    printf("%d %s", s.roll, s.name);
    return 0;
}

6. typedef struct + pointer

#include <stdio.h>

typedef struct {
    int x, y;
} Point;

int main() {
    Point p = {10, 20};
    printf("%d %d", p.x, p.y);
    return 0;
}

7. typedef with unsigned types

#include <stdio.h>

typedef unsigned long ULong;

int main() {
    ULong num = 999999;
    printf("%lu", num);
    return 0;
}

8. typedef for function pointer

#include <stdio.h>

typedef int (*FunPtr)(int,int);

int add(int a, int b) { return a + b; }

int main() {
    FunPtr f = add;
    printf("%d", f(5, 6));
    return 0;
}

Where typedef Is Used in Real Life?

• Microcontroller register mapping
• System libraries & header files
• Data structures (Linked list, trees, stack)
• OS kernel code
• Clean APIs for large projects

Practice Questions

1. What is typedef? Why is it used?
2. Write syntax of typedef for array.
3. Create typedef for structure Employee.
4. Create typedef for pointer to integer.
5. Difference between #define and typedef?

Practice Task