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Nested structs

Learn to use a struct inside another struct.

Nested structs

A struct member can be another struct. This is very useful to model complex data.

struct Point { int x; int y; };

struct Rectangle {
    struct Point topleft;
    struct Point bottomright;
};

Here Rectangle contains two Points: topleft and bottomright. To reach a nested member you use dots in a chain: r.topleft.x. This is the natural way to represent a rectangle by two corners.

Nested struct example

When declaring a Rectangle variable you can give the inner Points with nested braces.

struct Rectangle r = {
    {0, 0},
    {10, 5}
};
printf("%d %d\n",
    r.topleft.x,
    r.bottomright.y);
// "0 5"

Here the outer braces wrap the Rectangle, the inner braces wrap each Point. With r.topleft.x you get the top-left corner's x. This structure is very common in graphics and game programming.

Practice Print rectangle corners

Define struct Point (int x, int y). Define struct Rectangle (struct Point topleft, struct Point bottomright). In main create a variable r = {{0, 0}, {10, 5}} and print its four coordinates with printf.

Starter code

main.c
#include <stdio.h>

struct Point { int x; int y; };

/* Define struct Rectangle with topleft and bottomright Points */
int main(void) {
    /* Create a Rectangle; print its four coordinates with printf */
    return 0;
}

Sample solution

main.c
struct Rectangle { struct Point topleft; struct Point bottomright; };
struct Rectangle r = {{0, 0}, {10, 5}};
printf("%d %d %d %d\n", r.topleft.x, r.topleft.y, r.bottomright.x, r.bottomright.y);

Expected output

0 0 10 5

Questions and answers

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

1 Match expression to meaning

Term Meaning
r.topleft Top-left point
r.bottomright Bottom-right point
r.topleft.x x of top-left
struct Point Inner type

2 Fill in the blank: nested member

Question 
printf("%d
", r____);
Answer 
printf("%d
", r.topleft.x);

Explanation: r.topleft.x goes down to the nested member.

3 What does r.topleft.x give?

  • The x of bottomright
  • The x of the topleft point
  • The x of Rectangle Correct answer
  • A topleft pointer

Explanation: r.topleft.x gives the x of the topleft point.

All lessons in Beginner

1 C basics

  1. What is C?
  2. Your first program
  3. Compile and run
  4. Comments
  5. printf and escapes
  6. Summary - C basics

2 Variables

  1. Declaring variables
  2. Variable assignment
  3. const
  4. Variable scope
  5. typedef
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. char
  4. sizeof
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Menu loop
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 I/O

  1. printf formatting
  2. scanf
  3. Multiple inputs
  4. getchar and putchar
  5. puts and fputs
  6. Summary - I/O

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. break and continue
  5. Nested loops
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array size
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 Strings

  1. String basics
  2. String literals
  3. strlen
  4. strcpy and strcat
  5. strcmp
  6. Summary - Strings

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function prototypes
  5. Recursion
  6. Summary - Functions

13 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. NULL
  5. Pointer arithmetic
  6. Summary - Pointer basics

14 Arrays and pointers

  1. Array name as pointer
  2. Pointer to array
  3. Passing arrays to functions
  4. Pointer loop
  5. Multidim array pointer
  6. Summary - Arrays and pointers

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String functions

  1. strchr
  2. strstr
  3. strtok
  4. sprintf
  5. sscanf
  6. Summary - String functions

17 Structs

  1. Defining structs
  2. Using structs
  3. typedef struct
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Memory and stack

  1. Stack and heap
  2. Automatic storage
  3. malloc
  4. free
  5. calloc and realloc
  6. Summary - Memory and stack

19 Preprocessor

  1. #define
  2. #include
  3. Conditional compilation
  4. Macro functions
  5. Header files
  6. Summary - Preprocessor

20 Beginner final

  1. Project design
  2. Data model
  3. Functions
  4. Memory management
  5. Putting it together