Pointers to pointers in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a pointer to a pointer in C?

A pointer to a pointer is a variable that stores the address of another pointer variable. It allows indirect access to the value pointed to by the first pointer.

beginner

How do you declare a pointer to a pointer for an int variable?

You declare it as int **ptr; where ptr is a pointer to a pointer to an int.

intermediate

Given int x = 10; and int *p = &x;, how do you declare and assign a pointer to pointer pp?

Declare int **pp = &p;. Now pp points to p, which points to x.

intermediate

How do you access the value of x using the pointer to pointer pp?

Use **pp to get the value of x. The first * gets the pointer p, the second * gets the value x.

advanced

Why are pointers to pointers useful in C programming?

They are useful for dynamic memory management, passing pointers by reference to functions, and handling multi-dimensional arrays or complex data structures.

What does int **pp; declare?

A A pointer to an int

B A pointer to a pointer to an int

C An int variable

D A pointer to a char

int **pp; means pp is a pointer to a pointer to an int.

If int x = 5; and int *p = &x;, what is the type of &p?

A int **

B int &

C int

D int *

&p is the address of p, which is a pointer to int, so its type is int **.

How do you access the value of x using a pointer to pointer pp?

A *pp

B &pp

C pp

D **pp

Using **pp dereferences twice to get the value of x.

Which of the following is a valid assignment for a pointer to pointer?

A int **pp = p;

B int **pp = &x;

C int **pp = &p;

D int **pp = x;

pp must store the address of a pointer variable like p, so int **pp = &p; is correct.

Why might you pass a pointer to pointer to a function?

A To modify the pointer itself inside the function

B To pass an integer value

C To avoid using pointers

D To declare a new variable

Passing a pointer to pointer lets the function change the original pointer's value (e.g., allocate memory).

Explain what a pointer to pointer is and how you declare one in C.

Think about a pointer that points to another pointer.

Describe how to access the value of an int variable using a pointer to pointer.

Remember each * removes one level of indirection.