C Language Cheat Sheet

 C Language Cheat Sheet

Category	Concept	Description	Example
Basics	Hello World	Basic program to print "Hello, World!"	c #include <stdio.h>   int main() {  printf("Hello, World!\\n");  return 0; }
	Data Types	Fundamental types: int, float, double, char, etc.	c int a = 10; float b = 5.5; char c = 'A';
	Variables	Storage locations with type and name	c int age = 25; float salary = 50000.0;
	Operators	Arithmetic, Relational, Logical, Bitwise, Assignment operators	c int sum = a + b; if (a > b && b < c) { /*...*/ }
Control Flow	If-Else	Conditional branching	c if (score >= 50) {  printf("Pass"); } else {  printf("Fail"); }
	Switch	Multi-way branch based on variable value	c switch (choice) {  case 1: printf("One"); break;  case 2: printf("Two"); break;  default: printf("Other"); }
	Loops	for, while, do-while for iteration	c for(int i=0; i<10; i++) { printf("%d ", i); }
Functions	Function Declaration	Define reusable code blocks with parameters and return types	c int add(int x, int y); int add(int x, int y) { return x + y; }
	Recursion	Function calling itself	c int factorial(int n) {  if (n <= 1) return 1;  else return n * factorial(n - 1); }
Arrays & Strings	Arrays	Collection of elements of the same type	c int numbers[5] = {1, 2, 3, 4, 5};
	Strings	Array of characters terminated by null character \0	c char name[] = "Alice"; printf("Name: %s", name);
Pointers	Pointer Basics	Variables that store memory addresses	c int a = 10; int *ptr = &a; printf("%d", *ptr); // Outputs 10
	Pointer Arithmetic	Performing operations on pointers	c ptr++; // Moves to next integer location
	Pointers to Pointers	Pointers that store addresses of other pointers	c int **pptr = &ptr;
Structures	Structs	User-defined data types grouping different types	c struct Person {  char name[50];  int age; }; struct Person p1; p1.age = 30;
	Unions	Similar to structs but share the same memory location	c union Data {  int i;  float f;  char str[20]; }; union Data data; data.i = 10;
Memory Management	Dynamic Memory Allocation	Using malloc, calloc, realloc, and free to manage memory dynamically	c int *arr = malloc(5 * sizeof(int)); if(arr != NULL) { /* use array */ free(arr); }
File I/O	File Operations	Reading from and writing to files using fopen, fclose, fread, fwrite	c FILE *fp = fopen("file.txt", "r"); if (fp) { char buffer[100]; fgets(buffer, 100, fp); fclose(fp); }
Advanced	Bit Manipulation	Operations on individual bits using &, `	, ^, ~, <<, >>`
	Preprocessor Directives	Compile-time instructions using #define, #include, #ifdef, etc.	c #define PI 3.14 #include &lt;stdio.h&gt;
	Macros	Define code snippets that are expanded by the preprocessor	c #define SQUARE(x) ((x) * (x)) int sq = SQUARE(5);
	Enumerations	Define named integer constants	c enum Color { RED, GREEN, BLUE }; enum Color c = GREEN;
	Typedef	Create alias for data types	c typedef unsigned long ulong; ulong num = 1000;
Standard Library	Common Functions	Utilize functions from standard libraries like math.h, string.h	c #include <math.h> double result = sqrt(25.0); #include <string.h> int len = strlen("Hello");
Concurrency	Threads (POSIX)	Creating and managing threads using POSIX pthread library	c #include <pthread.h> void *print_message(void *ptr) { printf("%s", (char*)ptr); return NULL; } pthread_t thread; pthread_create(&thread, NULL, print_message, "Hello"); pthread_join(thread, NULL);
Networking	Sockets	Basic socket programming for network communication	c #include <sys/socket.h> // Create socket int sock = socket(AF_INET, SOCK_STREAM, 0);
Optimization	Inline Functions	Suggest compiler to inline functions for performance	c inline int max(int a, int b) { return (a > b) ? a : b; }
	Compiler Flags	Use flags like -O2, -Wall for optimization and warnings	bash gcc -O2 -Wall program.c -o program
Debugging	Using gdb	Debugging programs with GNU Debugger	bash gcc -g program.c -o program gdb ./program
Best Practices	Code Modularity	Write modular code using functions and separate files	Organize code into .c and .h files
	Commenting	Use comments to explain code logic	c // This function adds two numbers int add(int a, int b) { return a + b; }
Advanced Topics	Function Pointers	Pointers that reference functions for callbacks and dynamic behavior	c int add(int a, int b) { return a + b; } int (*func_ptr)(int, int) = &add; int result = func_ptr(2, 3);
	Dynamic Libraries	Create and use shared libraries (.so files)	Compile with gcc -shared -o libmylib.so -fPIC mylib.c and link with -lmylib
	Memory Alignment	Align data structures in memory for performance	c struct __attribute__((aligned(16))) AlignedStruct { int a; double b; };
	Concurrency Control	Use mutexes and semaphores to manage concurrent access	c #include <pthread.h> pthread_mutex_t lock; pthread_mutex_lock(&lock); // critical section pthread_mutex_unlock(&lock);
	Advanced Pointer Usage	Dangling pointers, wild pointers, pointer arithmetic complexities	Ensure pointers are initialized and managed properly to avoid undefined behavior
Error Handling	Return Codes	Use return values to indicate success or failure	c int readFile(const char *filename) {  FILE *fp = fopen(filename, "r");  if (!fp) return -1;  // ...  return 0; }
	errno and perror	Standard error reporting mechanisms	c #include <errno.h> #include <stdio.h> if (fopen("nonexistent.txt", "r") == NULL) {  perror("Error opening file"); }
Miscellaneous	Enum and Bitfields	Use enums for readable constants and bitfields for memory-efficient flags	c struct Flags {  unsigned int flag1 : 1;  unsigned int flag2 : 1; };
	Inline Assembly	Embed assembly code within C for low-level operations	c int a, b; asm ("addl %%ebx, %%eax;" : "=a" (a) : "a" (a), "b" (b));
Templates/Generics	Generic Programming	Use macros or void* to achieve generic-like functionality in C	c #define MAX(a,b) ((a) > (b) ? (a) : (b)) int max = MAX(5, 10);