C Pointers Cheat Sheet

int x = 10;int *p = &x;         // p stores the address of xprintf("%d\n", *p);  // dereference: prints 10*p = 20;              // modifies x through pint *nullPtr = NULL;  // always initialize pointersif (nullPtr != NULL) {    printf("%d\n", *nullPtr);}printf("size of pointer: %zu\n", sizeof(p));  // typically 8 on 64-bit systems

int arr[5] = {1, 2, 3, 4, 5};int *p = arr;              // equivalent to &arr[0]for (int i = 0; i < 5; i++) {    printf("%d ", *(p + i));  // same as arr[i]}// 2D array pointerint matrix[3][4];int (*rowPtr)[4] = matrix;    // pointer to an array of 4 intsprintf("%d\n", rowPtr[1][2]); // matrix[1][2]char *str = "hello";          // pointer to string literal (read-only)char buf[] = "hello";         // mutable copy on the stack

void increment(int *p) {    (*p)++;}int x = 5;increment(&x);   // x is now 6// function pointerint add(int a, int b) { return a + b; }int (*opPtr)(int, int) = add;printf("%d\n", opPtr(2, 3));   // 5// array of function pointersint subtract(int a, int b) { return a - b; }int (*ops[2])(int, int) = { add, subtract };printf("%d\n", ops[1](5, 3));  // 2

#include <stdlib.h>int *arr = malloc(10 * sizeof(int));   // uninitialized memoryif (arr == NULL) {    // allocation failed, handle error}int *zeroed = calloc(10, sizeof(int)); // zero-initialized memoryarr = realloc(arr, 20 * sizeof(int));  // grow/shrink existing allocationfree(arr);free(zeroed);arr = NULL;   // avoid dangling pointer after free