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
Collection of 50+ important C programs frequently asked in exams and interviews covering patterns, arrays, strings, numbers, recursion, and sorting algorithms.
This collection contains the most important C programs asked in exams, lab assignments, and interviews. Each program includes a working solution with output. Practice these to build strong programming fundamentals.
Number Programs
1. Check Prime Number
Example
#include <stdio.h>
int isPrime(int n) {
if (n <= 1) return 0;
if (n <= 3) return 1;
if (n % 2 == 0 || n % 3 == 0) return 0;
for (int i = 5; i * i <= n; i += 6)
if (n % i == 0 || n % (i + 2) == 0) return 0;
return 1;
}
int main() {
int num = 29;
printf("%d is %s\n", num, isPrime(num) ? "Prime" : "Not Prime");
return 0;
}
Output
29 is Prime
2. Fibonacci Series
Example
#include <stdio.h>
void fibonacci(int n) {
int a = 0, b = 1, next;
for (int i = 0; i < n; i++) {
printf("%d ", a);
next = a + b;
a = b;
b = next;
}
printf("\n");
}
int main() {
fibonacci(10);
return 0;
}
Output
0 1 1 2 3 5 8 13 21 34
3. Factorial (Iterative and Recursive)
Example
#include <stdio.h>
long factorialIterative(int n) {
long result = 1;
for (int i = 2; i <= n; i++) result *= i;
return result;
}
long factorialRecursive(int n) {
if (n <= 1) return 1;
return n * factorialRecursive(n - 1);
}
int main() {
printf("5! = %ld (iterative)\n", factorialIterative(5));
printf("5! = %ld (recursive)\n", factorialRecursive(5));
return 0;
}
Output
5! = 120 (iterative) 5! = 120 (recursive)
4. Reverse a Number
c example
#include <stdio.h>
int reverseNumber(int n) {
int reversed = 0;
while (n != 0) {
reversed = reversed * 10 + n % 10;
n /= 10;
}
return reversed;
}
int main() {
printf("Reverse of 12345: %d\n", reverseNumber(12345));
return 0;
}Output
Reverse of 12345: 54321
5. Check Palindrome Number
c example
#include <stdio.h>
int isPalindrome(int n) {
int original = n, reversed = 0;
while (n > 0) {
reversed = reversed * 10 + n % 10;
n /= 10;
}
return original == reversed;
}
int main() {
printf("121: %s\n", isPalindrome(121) ? "Palindrome" : "Not Palindrome");
printf("123: %s\n", isPalindrome(123) ? "Palindrome" : "Not Palindrome");
return 0;
}Output
121: Palindrome 123: Not Palindrome
6. Armstrong Number
Example
#include <stdio.h>
#include <math.h>
int isArmstrong(int n) {
int original = n, sum = 0, digits = 0, temp = n;
while (temp > 0) { digits++; temp /= 10; }
temp = n;
while (temp > 0) {
sum += (int)pow(temp % 10, digits);
temp /= 10;
}
return sum == original;
}
int main() {
printf("153: %s\n", isArmstrong(153) ? "Armstrong" : "Not Armstrong");
printf("370: %s\n", isArmstrong(370) ? "Armstrong" : "Not Armstrong");
return 0;
}
Output
153: Armstrong 370: Armstrong
7. GCD and LCM
c example
#include <stdio.h>
int gcd(int a, int b) {
while (b != 0) { int t = b; b = a % b; a = t; }
return a;
}
int lcm(int a, int b) { return (a / gcd(a, b)) * b; }
int main() {
printf("GCD(12, 18) = %d\n", gcd(12, 18));
printf("LCM(12, 18) = %d\n", lcm(12, 18));
return 0;
}Output
GCD(12, 18) = 6 LCM(12, 18) = 36
8. Power of a Number
c example
#include <stdio.h>
long power(int base, int exp) {
long result = 1;
while (exp > 0) {
if (exp % 2 == 1) result *= base;
base *= base;
exp /= 2;
}
return result;
}
int main() {
printf("2^10 = %ld\n", power(2, 10));
printf("3^5 = %ld\n", power(3, 5));
return 0;
}Output
2^10 = 1024 3^5 = 243
Array Programs
9. Find Largest and Smallest Element
Example
#include <stdio.h>
int main() {
int arr[] = {23, 55, 12, 89, 34, 7, 62};
int n = sizeof(arr) / sizeof(arr[0]);
int max = arr[0], min = arr[0];
for (int i = 1; i < n; i++) {
if (arr[i] > max) max = arr[i];
if (arr[i] < min) min = arr[i];
}
printf("Largest: %d, Smallest: %d\n", max, min);
return 0;
}
Output
Largest: 89, Smallest: 7
10. Reverse an Array
Example
#include <stdio.h>
void reverse(int arr[], int n) {
for (int i = 0; i < n / 2; i++) {
int temp = arr[i];
arr[i] = arr[n - 1 - i];
arr[n - 1 - i] = temp;
}
}
int main() {
int arr[] = {1, 2, 3, 4, 5};
reverse(arr, 5);
for (int i = 0; i < 5; i++) printf("%d ", arr[i]);
printf("\n");
return 0;
}
Output
5 4 3 2 1
11. Bubble Sort
Example
#include <stdio.h>
void bubbleSort(int arr[], int n) {
for (int i = 0; i < n - 1; i++)
for (int j = 0; j < n - i - 1; j++)
if (arr[j] > arr[j+1]) {
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
int main() {
int arr[] = {64, 34, 25, 12, 22, 11, 90};
int n = 7;
bubbleSort(arr, n);
for (int i = 0; i < n; i++) printf("%d ", arr[i]);
printf("\n");
return 0;
}
Output
11 12 22 25 34 64 90
12. Binary Search
Example
#include <stdio.h>
int binarySearch(int arr[], int n, int target) {
int low = 0, high = n - 1;
while (low <= high) {
int mid = low + (high - low) / 2;
if (arr[mid] == target) return mid;
else if (arr[mid] < target) low = mid + 1;
else high = mid - 1;
}
return -1;
}
int main() {
int arr[] = {2, 5, 8, 12, 16, 23, 38, 45, 56, 72};
int result = binarySearch(arr, 10, 23);
printf("Found at index: %d\n", result);
return 0;
}
Output
Found at index: 5
String Programs
13. Reverse a String
Example
#include <stdio.h>
#include <string.h>
void reverseString(char *str) {
int len = strlen(str);
for (int i = 0; i < len / 2; i++) {
char temp = str[i];
str[i] = str[len - 1 - i];
str[len - 1 - i] = temp;
}
}
int main() {
char str[] = "Hello World";
reverseString(str);
printf("Reversed: %s\n", str);
return 0;
}
Output
Reversed: dlroW olleH
14. Check String Palindrome
Example
#include <stdio.h>
#include <string.h>
int isStringPalindrome(const char *str) {
int left = 0, right = strlen(str) - 1;
while (left < right) {
if (str[left] != str[right]) return 0;
left++; right--;
}
return 1;
}
int main() {
printf("madam: %s\n", isStringPalindrome("madam") ? "Palindrome" : "Not");
printf("hello: %s\n", isStringPalindrome("hello") ? "Palindrome" : "Not");
return 0;
}
Output
madam: Palindrome hello: Not
15. Count Vowels and Consonants
Example
#include <stdio.h>
#include <ctype.h>
void countChars(const char *str) {
int vowels = 0, consonants = 0, digits = 0, spaces = 0;
for (int i = 0; str[i]; i++) {
char c = tolower(str[i]);
if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') vowels++;
else if (isalpha(c)) consonants++;
else if (isdigit(c)) digits++;
else if (c == ' ') spaces++;
}
printf("Vowels: %d, Consonants: %d, Digits: %d, Spaces: %d\n",
vowels, consonants, digits, spaces);
}
int main() {
countChars("Hello World 123");
return 0;
}
Output
Vowels: 3, Consonants: 7, Digits: 3, Spaces: 2
Pattern Programs
16. Star Pyramid
Example
#include <stdio.h>
int main() {
int rows = 5;
for (int i = 1; i <= rows; i++) {
for (int j = rows - i; j > 0; j--) printf(" ");
for (int j = 1; j <= 2*i-1; j++) printf("*");
printf("\n");
}
return 0;
}
Output
* *** ***** ******* *********
17. Number Triangle
Example
#include <stdio.h>
int main() {
int rows = 5;
for (int i = 1; i <= rows; i++) {
for (int j = 1; j <= i; j++)
printf("%d ", j);
printf("\n");
}
return 0;
}
Output
1 1 2 1 2 3 1 2 3 4 1 2 3 4 5
Recursion Programs
18. Tower of Hanoi
c example
#include <stdio.h>
void hanoi(int n, char from, char to, char aux) {
if (n == 0) return;
hanoi(n - 1, from, aux, to);
printf("Move disk %d: %c -> %c\n", n, from, to);
hanoi(n - 1, aux, to, from);
}
int main() {
hanoi(3, 'A', 'C', 'B');
return 0;
}Output
Move disk 1: A -> C Move disk 2: A -> B Move disk 1: C -> B Move disk 3: A -> C Move disk 1: B -> A Move disk 2: B -> C Move disk 1: A -> C
19. Sum of Digits (Recursive)
c example
#include <stdio.h>
int sumDigits(int n) {
if (n == 0) return 0;
return n % 10 + sumDigits(n / 10);
}
int main() {
printf("Sum of digits of 12345: %d\n", sumDigits(12345));
return 0;
}Output
Sum of digits of 12345: 15
Sorting Algorithms
20. Selection Sort
Example
#include <stdio.h>
void selectionSort(int arr[], int n) {
for (int i = 0; i < n - 1; i++) {
int minIdx = i;
for (int j = i + 1; j < n; j++)
if (arr[j] < arr[minIdx]) minIdx = j;
int temp = arr[i]; arr[i] = arr[minIdx]; arr[minIdx] = temp;
}
}
int main() {
int arr[] = {29, 10, 14, 37, 13};
selectionSort(arr, 5);
for (int i = 0; i < 5; i++) printf("%d ", arr[i]);
printf("\n");
return 0;
}
Output
10 13 14 29 37
21. Insertion Sort
Example
#include <stdio.h>
void insertionSort(int arr[], int n) {
for (int i = 1; i < n; i++) {
int key = arr[i], j = i - 1;
while (j >= 0 && arr[j] > key) {
arr[j + 1] = arr[j];
j--;
}
arr[j + 1] = key;
}
}
int main() {
int arr[] = {12, 11, 13, 5, 6};
insertionSort(arr, 5);
for (int i = 0; i < 5; i++) printf("%d ", arr[i]);
printf("\n");
return 0;
}
Output
5 6 11 12 13
Quick Reference: All Programs
| # | Program | Key Concept |
|---|---|---|
| 1-8 | Number programs | Loops, modulus, recursion |
| 9-12 | Array programs | Indexing, searching, sorting |
| 13-15 | String programs | Character arrays, traversal |
| 16-17 | Pattern programs | Nested loops |
| 18-19 | Recursion | Base case, divide & conquer |
| 20-21 | Sorting | Comparison-based algorithms |
Summary
These programs form the foundation of C programming proficiency. Each one teaches a specific concept – from basic loops and conditions to recursion and algorithms. Practice writing them from memory, then try variations (e.g., reverse pyramid, merge sort, string compression). The ability to code these quickly and correctly is what interviewers and examiners look for.
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Important C Programs – 50+ Frequently Asked Programs with Solutions.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this C Programming topic.
Search Terms
c-programming, c programming, programming, resources, important, programs, important c programs – 50+ frequently asked programs with solutions
Related C Programming Topics
Continue learning this concept
ResourcesCommon C Programming Errors and Solutions – Debugging GuideFix common C programming errors including segmentation fault, memory leaks, buffer overflow, undefined behavior, linker errors, and compilation warnings with solutions.ResourcesQuick Revision Notes for C Programming – Complete C in 10 MinutesFast-paced C programming revision notes covering all topics from basics to advanced in a concise format. Perfect for last-minute exam preparation and quick review.ResourcesRecommended C Programming Books – From Beginner to ExpertCurated list of the best C programming books for beginners, intermediate, and advanced programmers including K&R, Expert C Programming, and modern C resources.ArraysArray Programs in C - Reverse, Rotate, Duplicates, MergePractice essential array programs in C including reversing arrays, rotating elements, finding duplicates, merging sorted arrays, and more coding problems with solutions.PointersPointer Programs in C - Swap, String Reversal, Dynamic AllocationPractice essential pointer programs in C including swap using pointers, string operations with pointers, dynamic memory allocation, and pointer-based data manipulation.StringsString Programs in C - Anagram, Word Count, Vowels, FrequencyPractice essential string programs in C including anagram check, word count, vowel count, character frequency, remove duplicates, and more coding problems.