C Notes
HubApplications of C Programming LanguageFeatures of C Programming LanguageHistory of C Programming LanguageWhat is C Language?Why Learn C Programming in 2024?First C Program - Hello World in C with ExplanationGCC Compiler - Complete Guide to GNU C CompilerInstall C Compiler on Linux - GCC Setup Guide for All DistrosInstall C Compiler on macOS - Xcode Command Line Tools and Homebrew GCCInstall C Compiler on Windows - MinGW, MSYS2, and WSL GuideSetup VS Code for C Programming - Complete Configuration GuideC Syntax Rules — Complete GuideComments in C ProgrammingConstants in C ProgrammingData Types in CIdentifiers in C ProgrammingKeywords in C ProgrammingStructure of a C ProgramVariables in C ProgrammingArithmetic Operators in C ProgrammingAssignment Operators in C ProgrammingBitwise Operators in C ProgrammingIncrement and Decrement Operators in CLogical Operators in C ProgrammingRelational Operators in C ProgrammingTernary Operator in C ProgrammingBreak Statement in C ProgrammingContinue Statement in C ProgrammingDo-While Loop in C ProgrammingFor Loop in C ProgrammingGoto Statement in C Programmingif-else Statement in C Programmingif Statement in C ProgrammingNested if Statements in C ProgrammingSwitch Statement in C ProgrammingWhile Loop in C ProgrammingFunction Arguments in C - Pass by Value vs Pass by ReferenceFunction Call in C ProgrammingFunction Declaration (Prototype) in CFunction Definition in C ProgrammingIntroduction to Functions in C ProgrammingRecursion in C ProgrammingReturn Statement in C ProgrammingStorage Classes in C ProgrammingArray Operations in C - Searching, Sorting, Insert and DeleteArray Programs in C - Reverse, Rotate, Duplicates, MergeIntroduction to Arrays in C ProgrammingMultidimensional Arrays in C ProgrammingOne Dimensional Arrays in C ProgrammingPassing Arrays to Functions in CTwo Dimensional Arrays in C ProgrammingString Comparison in C - strcmp, strncmp, Case-InsensitiveString Functions in C - strlen, strcpy, strcat, strcmpC String Handling Library - Complete string.h ReferenceString Manipulation in C - Reverse, Uppercase, PalindromeString Programs in C - Anagram, Word Count, Vowels, FrequencyStrings in C Programming - Complete IntroductionDouble Pointers in C - Pointer to PointerPointer Arithmetic in C ProgrammingPointer Declaration and Initialization in CPointer Programs in C - Swap, String Reversal, Dynamic AllocationPointers and Arrays in C - The Relationship ExplainedPointers and Functions in C - Pass by ReferenceIntroduction to Pointers in C ProgrammingVoid Pointers in C - Generic Pointers Guidecalloc() in C – Contiguous Memory AllocationDynamic Arrays in C – Runtime-Sized Arraysfree() in C – Releasing Dynamic Memorymalloc() in C – Dynamic Memory AllocationMemory Management Best Practices in Crealloc() in C – Resizing Dynamic MemoryBinary Files in C – fread and fwriteFile Handling in C – IntroductionFile Handling Projects in C – Student Records & Phone BookFile Modes in C – Complete Guidefopen() and fclose() in C – Opening and Closing FilesReading Files in C – fgetc, fgets, fscanf, freadWriting Files in C – fputc, fputs, fprintf, fwriteConditional Compilation in C – #ifdef, #ifndef, #if#define Macros in C – Constants and Macro FunctionsHeader Files in C – Creating Custom Headers#include Directive in C – File InclusionMacro Functions in C – Parameterized MacrosC Preprocessor – Overview and DirectivesGraphs in C – Adjacency Matrix, Adjacency List, BFS, and DFSHash Tables in C – Implementation, Collision Handling, and ChainingLinked List in C – Singly, Doubly, and Circular with ImplementationQueue in C – Linear, Circular, and Priority Queue ImplementationStack in C – Array and Linked List Implementation with ApplicationsTrees in C – Binary Search Tree Implementation with TraversalsC Programming Best Practices – Coding Standards, Safety, and PerformanceBit Fields in C – Definition, Use Cases, and Protocol HeadersC Standard Library Overview – All Headers and Common FunctionsCommand Line Arguments in C – argc and argv ExplainedDebugging Techniques in C – GDB, Valgrind, and SanitizersFunction Pointers in C – Complete Guide with ExamplesMemory Layout of a C Program – Text, Data, BSS, Heap, StackBank Management System in C – Complete Project with File StorageFile Encryption Tool in C – XOR Cipher ImplementationLibrary Management System in C – Complete Project with Source CodeMini Compiler in C – Lexer and Parser for Simple ExpressionsSnake Game in C – Console-Based Game with Source CodeStudent Management System in C – Complete Project with Source CodeC Programming Cheatsheet – Complete Quick Reference GuideTop 50 C Programming Interview Questions with Answers (2025)Memory Management Interview Questions in C with AnswersOutput Prediction Questions in C – What Will This Program Print?Pointer Interview Questions in C – Tricky Problems with AnswersCommon C Programming Errors and Solutions – Debugging GuideImportant C Programs – 50+ Frequently Asked Programs with SolutionsQuick Revision Notes for C Programming – Complete C in 10 MinutesRecommended C Programming Books – From Beginner to ExpertFormat Specifiers in C - Complete Referencegetchar() and putchar() in C Programminggets() and puts() in C ProgrammingC Input Output Programs and Examplesprintf() Function in C Programmingscanf() Function in C ProgrammingArrays of Structures in C – Managing CollectionsEnums in C – Enumerated Data TypesNested Structures in C – Struct Within StructPointers to Structures in C – Arrow OperatorStructures in C – User-Defined Data Typestypedef in C – Creating Type AliasesUnions in C – Shared Memory Data Types
Comprehensive C programming cheatsheet covering syntax, data types, operators, control flow, pointers, strings, file I/O, memory management, and common patterns.
This cheatsheet provides a compact reference for all essential C programming concepts. Keep it handy during coding, revision, or interview preparation.
Data Types and Sizes
c example
// Integer types
char c = 'A'; // 1 byte (-128 to 127)
short s = 32767; // 2 bytes (-32768 to 32767)
int i = 2147483647; // 4 bytes
long l = 2147483647L; // 4 or 8 bytes
long long ll = 9223372036854775807LL; // 8 bytes
// Unsigned variants (no negative values, double positive range)
unsigned char uc = 255;
unsigned int ui = 4294967295U;
unsigned long long ull = 18446744073709551615ULL;
// Floating point
float f = 3.14f; // 4 bytes, ~7 digits precision
double d = 3.14159265; // 8 bytes, ~15 digits precision
// Boolean (C99)
#include <stdbool.h>
bool flag = true;| Type | Size | Range |
|---|---|---|
| char | 1B | -128 to 127 |
| unsigned char | 1B | 0 to 255 |
| short | 2B | -32,768 to 32,767 |
| int | 4B | -2.1B to 2.1B |
| long long | 8B | -9.2×10¹⁸ to 9.2×10¹⁸ |
| float | 4B | ±3.4×10³⁸ |
| double | 8B | ±1.7×10³⁰⁸ |
Format Specifiers
c example
printf("%d", intVar); // int
printf("%ld", longVar); // long
printf("%lld", llVar); // long long
printf("%u", unsignedVar); // unsigned int
printf("%f", floatVar); // float/double
printf("%.2f", doubleVar); // 2 decimal places
printf("%e", doubleVar); // scientific notation
printf("%c", charVar); // character
printf("%s", stringVar); // string
printf("%p", (void*)ptr); // pointer address
printf("%x", intVar); // hexadecimal
printf("%o", intVar); // octal
printf("%%"); // literal %
printf("%05d", num); // zero-padded, width 5
printf("%-10s", str); // left-aligned, width 10
printf("%zu", sizeof(x)); // size_tOperators (by Precedence, High to Low)
| Precedence | Operators | Associativity | ||
|---|---|---|---|---|
| 1 | () [] -> . | Left to Right | ||
| 2 | ! ~ ++ -- + - * & (type) sizeof | Right to Left | ||
| 3 | * / % | Left to Right | ||
| 4 | + - | Left to Right | ||
| 5 | << >> | Left to Right | ||
| 6 | < <= > >= | Left to Right | ||
| 7 | == != | Left to Right | ||
| 8 | & | Left to Right | ||
| 9 | ^ | Left to Right | ||
| 10 | ` | ` | Left to Right | |
| 11 | && | Left to Right | ||
| 12 | ` | ` | Left to Right | |
| 13 | ?: | Right to Left | ||
| 14 | = += -= etc. | Right to Left | ||
| 15 | , | Left to Right |
Control Flow
Example
// If-else
if (condition) { ... }
else if (condition2) { ... }
else { ... }
// Switch
switch (expression) {
case value1: ...; break;
case value2: ...; break;
default: ...;
}
// Loops
for (int i = 0; i < n; i++) { ... }
while (condition) { ... }
do { ... } while (condition);
// Jump statements
break; // Exit loop/switch
continue; // Skip to next iteration
return val; // Exit function
goto label; // Jump to label (use sparingly)
Pointers Quick Reference
Example
int x = 10;
int *p = &x; // p stores address of x
int val = *p; // Dereference: val = 10
*p = 20; // Modify x through pointer
int **pp = &p; // Pointer to pointer
**pp = 30; // x is now 30
// Pointer arithmetic
int arr[5] = {10, 20, 30, 40, 50};
int *ptr = arr;
*(ptr + 2) == 30 // Move 2 elements forward
ptr[2] == 30 // Same thing
// Function pointers
int (*fp)(int, int) = &add;
int result = fp(3, 4);
// void pointer (generic)
void *vp = &x;
int val = *(int*)vp; // Must cast before dereference
// NULL check
if (ptr != NULL) { /* safe to use */ }
Strings
c example
#include <string.h>
char str[] = "Hello"; // Modifiable, 6 bytes
char *ptr = "Hello"; // Read-only literal
strlen(str); // Length (5, excludes '\0')
strcpy(dest, src); // Copy (unsafe)
strncpy(dest, src, n); // Copy with limit
strcat(dest, src); // Concatenate
strcmp(s1, s2); // Compare (0 if equal)
strstr(haystack, needle); // Find substring
strchr(str, 'c'); // Find character
strtok(str, delimiters); // Tokenize
sprintf(buf, "%d", num); // Format to string
snprintf(buf, size, fmt, ...) // Safe formatArrays
Example
int arr[5] = {1, 2, 3, 4, 5}; // Static array
int arr[5] = {0}; // All zeros
int arr[] = {1, 2, 3}; // Size inferred (3)
int matrix[3][4] = {{0}}; // 2D array, all zeros
// Array size calculation
int n = sizeof(arr) / sizeof(arr[0]);
// Arrays decay to pointers when passed to functions
void func(int *arr, int size); // Receives pointer
Structures and Unions
c example
// Structure
struct Point {
int x;
int y;
};
struct Point p1 = {10, 20};
p1.x = 30;
// Pointer to struct
struct Point *pp = &p1;
pp->x = 40; // arrow operator
// typedef
typedef struct { int x, y; } Point;
Point p = {1, 2};
// Union (shared memory)
union Data { int i; float f; char c; };
union Data d;
d.i = 65; // d.c is now 'A'Dynamic Memory
c example
#include <stdlib.h>
int *p = (int*)malloc(n * sizeof(int)); // Uninitialized
int *p = (int*)calloc(n, sizeof(int)); // Zero-initialized
p = (int*)realloc(p, new_size); // Resize
free(p); p = NULL; // Free and nullify
// Always check!
if (p == NULL) { /* handle error */ }File I/O
Example
#include <stdio.h>
FILE *fp = fopen("file.txt", "r"); // Open
if (!fp) { perror("fopen"); exit(1); }
// Reading
char line[256];
fgets(line, sizeof(line), fp); // Read line
fscanf(fp, "%d", &num); // Formatted read
int ch = fgetc(fp); // Read char
fread(buf, size, count, fp); // Binary read
// Writing
fprintf(fp, "Value: %d\n", x); // Formatted write
fputs("text", fp); // Write string
fputc('A', fp); // Write char
fwrite(buf, size, count, fp); // Binary write
// Position
fseek(fp, offset, SEEK_SET); // Move position
long pos = ftell(fp); // Get position
rewind(fp); // Go to beginning
fclose(fp); // Close file
// File modes: "r" "w" "a" "rb" "wb" "r+" "w+" "a+"
Preprocessor
c example
#include <stdio.h> // System header
#include "myheader.h" // Local header
#define PI 3.14159 // Constant macro
#define MAX(a,b) ((a)>(b)?(a):(b)) // Function macro
#define STRINGIFY(x) #x // Stringification
#define CONCAT(a,b) a##b // Token pasting
#ifdef DEBUG
// Compiled only if DEBUG is defined
#endif
#ifndef HEADER_H
#define HEADER_H
// Include guard
#endif
#pragma once // Modern include guardCommon Patterns
Example
// Swap without temp
a ^= b; b ^= a; a ^= b;
// Check power of 2
(n > 0) && ((n & (n-1)) == 0)
// Set bit i
num |= (1 << i);
// Clear bit i
num &= ~(1 << i);
// Toggle bit i
num ^= (1 << i);
// Check bit i
(num >> i) & 1
// Get array length
#define ARRAY_LEN(arr) (sizeof(arr)/sizeof(arr[0]))
// Min/Max
#define MIN(a,b) ((a)<(b)?(a):(b))
#define MAX(a,b) ((a)>(b)?(a):(b))
// Safe free
#define SAFE_FREE(p) do { free(p); p = NULL; } while(0)
Common Library Functions
c example
// stdlib.h
abs(x) // Absolute value
atoi(str) // String to int
atof(str) // String to double
strtol(str,&end,base) // Safe string to long
rand() % n // Random 0 to n-1
srand(seed) // Seed random
qsort(arr,n,size,cmp) // Sort array
bsearch(key,arr,n,size,cmp) // Binary search
exit(status) // Terminate program
system(cmd) // Execute shell command
// math.h (link with -lm)
sqrt(x) pow(x,y) fabs(x)
ceil(x) floor(x) round(x)
sin(x) cos(x) tan(x)
log(x) log10(x) log2(x)
// ctype.h
isalpha(c) isdigit(c) isspace(c)
isalnum(c) isupper(c) islower(c)
toupper(c) tolower(c)Compilation Commands
c example
gcc file.c -o output // Basic compile
gcc -Wall -Wextra -g file.c // With warnings + debug
gcc -O2 file.c // Optimized
gcc -std=c11 file.c // C11 standard
gcc -lm file.c // Link math library
gcc -fsanitize=address file.c // With ASanSummary
This cheatsheet covers the most essential C programming syntax and patterns. Keep it as a quick reference while coding or before interviews. Remember: C trusts the programmer – always validate inputs, check allocations, and free memory. Compile with -Wall -Wextra to catch common mistakes at compile time.
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for C Programming Cheatsheet – Complete Quick Reference Guide.
Interview Use
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