This article contains exercises that will test your knowledge of pointers. If you find yourself struggling with any of these questions, feel free to ask for help by emailing me at joseph@vertstudios.com.

If you are uncomfortable or unfamiliar with pointers, please view (and understand!) the following videos before progressing to the exercises:

1. Beginner's introduction to pointers in C
2. Malloc and functions returning pointers

Problems

Problem 1

Write a swap() function with the following function header:

void swap(int *p1, int *p2);

Use this function to swap the values of two integers.

int main(){
    int x = 10;
    int y = 20;

     // You must figure out how to call the function correctly!
    swap(...)

    // Should print out x: 20, y: 10
    printf("x: %d, y: %d\n", x, y);
}

Problem 2

Write a program that demonstrates the fact that arrays themselves are not passed to functions, but a pointer to the first element of the array is what is passed.

Hint: The sizeof operator will be useful.

Problem 3

According to the C standard, arr[0] is actually syntactic shorthand for *(arr+0). Write a program that prints all elements of an integer array using this alternative notation.

Problem 4

Create a simple function print_addr(int x) whose sole purpose is to print the address of the integer x passed to it. Create an integer variable in main, print out its address, and then pass that variable to print_addr. Compare the results. Is this expected behavior?

Problem 5

Create a function new_integer() that declares and initializes an integer inside the function and returns the address of that integer. Print out the integer value associated with this memory address in main. Is this legal C? Does your complier display warnings? Is this a safe operation?

Problem 6

Create a function print_array which will print out all values of an integer array. What parameters must the function have in order to work for any integer array?

Problem 7

Write a program which uses an ARR_SIZE constant via #define ARR_SIZE 10. Create a function that allocates memory for ARR_SIZE integers, assigns the 0th integer to 0, the 1st integer to 1, and so on, and returns the address of the allocated space. (Your array should look like [0|1|2|...]). use the print_array function from problem 6 above to print out each element of the allocated array. After you have successfully made the program, alter the value of ARR_SIZE and observe the results.

Tagged as c