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typedef and array

  • C course
  • Intermediate
  • Lesson 108/116
  • 5 min

Learn to define array types with typedef.

typedef and array

typedef also names array types. Multi-dimensional arrays have complex syntax; typedef simplifies the code.

Example: typedef int Matrix[3][3];. This names a 3×3 integer matrix type Matrix. From then on you write Matrix m; instead of int m[3][3];. Each element is accessed as m[i][j]. This pattern is common in mathematical calculations and game board representation. The type name reflects the purpose; when someone writes Matrix, everyone expects a 3×3 integer matrix.

Matrix initialization

You initialize a Matrix variable with nested brace lists. Each inner list represents a row.

Example: Matrix m = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };. This lays out the numbers 1 through 9 in a 3×3 grid. m[0][0] = 1, m[1][1] = 5, m[2][2] = 9. Inner braces separate rows; they improve readability. This structure is the basis of matrix operations and tabular data. Thanks to typedef, it is declared concisely and meaningfully as Matrix.

Practice Write a Matrix program

Define typedef int Matrix[3][3];. In main create Matrix m = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };. Print the center element with printf("%d\n", m[1][1]);.

Starter code

main.c
#include <stdio.h>

// Define the Matrix type with typedef
// Initialize m with values
// Print m[1][1]

int main(void) {
    return 0;
}

Sample solution

main.c
#include <stdio.h>

typedef int Matrix[3][3];

int main(void) {
    Matrix m = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };
    printf("%d\n", m[1][1]);
    return 0;
}

Expected output

5

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Complete the matrix access

Question 
printf("%d
", m[1][____]);
Answer 
printf("%d
", m[1][1]);

Explanation: m[1][1] is the center element of the matrix.

2 Match the matrix indices

Term Meaning
m[0][0] Top left
m[1][1] Center
m[2][2] Bottom right
Matrix Type name

3 What does typedef int Matrix[3][3]; define?

  • A 3-element array
  • A 3×3 integer matrix type Correct answer
  • A pointer type
  • A function type

Explanation: Matrix is a 3×3 integer two-dimensional array type.

All lessons in Intermediate

1 Advanced pointers

  1. Pointer to pointer
  2. Array of pointers
  3. Function pointers
  4. Function pointer parameter
  5. void pointer
  6. Summary - Advanced pointers

2 Memory management

  1. Dynamic array
  2. Resize with realloc
  3. Memory leaks
  4. Dangling pointers
  5. Allocation patterns
  6. Summary - Memory management

3 Project: Helper library

  1. Module design
  2. String helpers
  3. Number helpers
  4. Array helpers
  5. Putting it together

4 Advanced string handling

  1. Dynamic strings
  2. String concatenation
  3. String search
  4. String conversion
  5. String safety
  6. Summary - Advanced strings

5 Function pointers

  1. Function pointer definition
  2. Calling function pointers
  3. qsort
  4. Callback patterns
  5. Function pointer array
  6. Summary - Function pointers

6 Advanced structs

  1. Structs and pointers
  2. Dynamic struct
  3. Struct and function
  4. Nested structs
  5. Array of structs
  6. Summary - Advanced structs

7 Unions and enums

  1. union
  2. enum
  3. Struct and union
  4. typedef enum
  5. Bit fields
  6. Summary - Unions and enums

8 Project: Quiz app

  1. Quiz model
  2. Adding questions
  3. Running the quiz
  4. Score calculation
  5. Putting it together

9 File I/O

  1. FILE and fopen
  2. fprintf and fscanf
  3. fgets and fputs
  4. fclose
  5. fread and fwrite
  6. Summary - File I/O

10 Error handling

  1. errno
  2. perror
  3. strerror
  4. assert
  5. Error return values
  6. Summary - Error handling

11 Multi-file projects

  1. Headers and sources
  2. extern
  3. static
  4. Makefile basics
  5. Multiple modules
  6. Summary - Multi-file

12 Project: Library app

  1. Model design
  2. Library module
  3. Checking out
  4. Search and filter
  5. Putting it together

13 Dynamic data structures

  1. Linked list
  2. Adding to list
  3. Traversing list
  4. Deleting from list
  5. Stack and queue
  6. Summary - Dynamic data

14 Variable arguments

  1. stdarg.h
  2. va_start and va_end
  3. printf-like function
  4. vsnprintf
  5. Variadic patterns
  6. Summary - Variable arguments

15 Standard library

  1. stdlib.h
  2. string.h
  3. math.h
  4. time.h
  5. ctype.h
  6. Summary - Standard library

16 Command-line arguments

  1. argc and argv
  2. Argument processing
  3. getopt
  4. Argument validation
  5. Exit codes
  6. Summary - Command line

17 Debugging

  1. gdb basics
  2. Breakpoints
  3. Watch and print
  4. valgrind
  5. printf debugging
  6. Summary - Debugging

18 Advanced bitwise

  1. Bit masking
  2. Set and clear bits
  3. Bit shifting
  4. Bit hacks
  5. Pack and unpack
  6. Summary - Advanced bitwise

19 Advanced typedef

  1. typedef and struct
  2. typedef and function pointer
  3. typedef and array
  4. Opaque types
  5. typedef and enum
  6. Summary - Advanced typedef

20 Intermediate final

  1. Project design
  2. Data model
  3. Functional logic
  4. File I/O
  5. Putting it together