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Summary - Pointer basics

Combine &, * and NULL to write a swap function.

Summary: Pointer basics

In this group you saw the basics of pointers. A pointer holds a memory address; & takes the address, * accesses the value.

  • int *ptr: int pointer declaration
  • &x: x's address
  • *ptr: the value ptr points to
  • NULL: null pointer; safe starting point
  • ptr + 1: jumps to the next element

Now let's combine these in one task.

Practice Read and print a value via a pointer

Define int x = 15;. Bind with int *ptr = &x;. Print the value ptr points to with printf("%d\n", *ptr);. Output should be 15.

Starter code

main.c
#include <stdio.h>

int main(void) {
    int x = 15;
    /* bind ptr to x */
    /* print *ptr with printf %d */
    return 0;
}

Sample solution

main.c
#include <stdio.h>

int main(void) {
    int x = 15;
    int *ptr = &x;
    printf("%d\n", *ptr);
    return 0;
}

Expected output

15

Questions and answers

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

1 Which operator gives a variable's address?

  • & Correct answer
  • *
  • +
  • -

Explanation: Answer is &. The & operator takes a variable's address.

2 NULL check

Question 
int *p = NULL;
if (p ____) { /* not safe */ }
Answer 
int *p = NULL;
if (p == NULL) { /* not safe */ }

Explanation: p == NULL checks for null.

3 Match pointer concepts

Term Meaning
& takes address
* dereferences
NULL null pointer
ptr + 1 next element

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