C Pointers

A pointer stores the memory address of another variable. &x is the address of x; *p follows a pointer to the value it points at. Pointers let functions change the caller's variables.

ExampleC

#include <stdio.h>

void addOne(int *p) {
  *p = *p + 1;
}

int main(void) {
  int x = 10;
  int *p = &x;
  printf("%d\n", *p);   // 10: value through the pointer
  *p = 20;
  printf("%d\n", x);    // 20: x changed

  addOne(&x);
  printf("%d\n", x);    // 21

  int nums[3] = {1, 2, 3};
  int *q = nums;
  printf("%d %d\n", *q, *(q + 2)); // 1 3
  return 0;
}

Output

Arrays and pointers are closely related: the name of an array acts like a pointer to its first element, which is why *(q + 2) reaches the third item.

Quick check

What does *p mean when p is a pointer?

The address of pThe value p points toMultiply by p

Finish the quick check (and any code exercise) to complete this lesson, or mark it done yourself.

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