Top 50 C Coding Interview Questions and Answers (2024) (2024)

// C Program to find // Largest of three numbers#include <stdio.h>int main(){ int a = 1, b = 2, c = 3; // condition for a is greatest if (a > b && a > c) printf("%d", a); // condition for b is greatest else if (b > a && b > c) printf("%d", b); // remaining conditions // c is greatest else printf("%d", c); return 0;}

// C Program for// Checking value is// Prime or not#include <stdio.h>int main(){ int N = 91; int flag = 0; // Iterate from 2 to N/2 for (int i = 2; i <= N / 2; i++) { // If n is divisible by any number between 2 and // n/2, it is not prime if (N % i == 0) { flag = 1; break; } } if (flag == 0) printf("Not a Prime Number"); else printf("Is a Prime Number"); return 0;}

// C program to calculate Compound Interest#include <stdio.h>// For using pow function we must// include math.h#include <math.h>// Driver codeint main(){ // Principal amount double principal = 2300; // Annual rate of interest double rate = 7; // Time double time = 4; // Calculating compound Interest double amount = principal * ((pow((1 + rate / 100), time))); double CI = amount - principal; printf("Compound Interest is : %lf", CI); return 0;}

// C Program to// Swap two numbers// No Extra Space#include <stdio.h>int main(){ int x = 10; int y = 20; printf("x: %d , y: %d\n", x, y); // Code to swap 'x' and 'y' x = x + y; y = x - y; x = x - y; printf("x: %d , y: %d\n", x, y); return 0;}

// C Program for// Replacing 0 to 1#include <math.h>#include <stdio.h>int main(){ int N = 102301; int ans = 0; int i = 0; while (N != 0) { // Condition to change value if (N % 10 == 0) ans = ans + 1 * pow(10, i); else ans = ans + (N % 10) * pow(10, i); N = N / 10; i++; } printf("%d", ans); return 0;}

// C Program for converting// binary to decimal#include <stdio.h>int main(){ int N = 11011; // Initializing base value a to 1 int a = 1; int ans = 0; while (N != 0) { ans = ans + (N % 10) * a; N = N / 10; a = a * 2; } printf("%d", ans); return 0;}

// C Program to check// Year is leap year or not#include <stdio.h>// Function Declaration to check leap yearvoid leap_year(int year){ // If a year is multiple of 400, then leap year if (year % 400 == 0) printf("%d is a leap year.\n", year); // If a year is multiple of 100, then not a leap year else if (year % 100 == 0) printf("%d is not a leap year.\n", year); // If a year is multiple of 4, then leap year else if (year % 4 == 0) printf("%d is a leap year.\n", year); // Not leap year else printf("%d is not a leap year.\n", year);}int main(){ leap_year(2000); leap_year(2002); leap_year(2008); return 0;}

// C Program to calculate// Factorial of a number#include <stdio.h>// Calculating factorial using iterationvoid factorial_iteration(int N){ unsigned long long int ans = 1; for (int i = 1; i <= N; i++) { ans = ans * i; } printf("Factorial of %d is %lld\n", N, ans);}// Calculating factorial using recursionint factorial(int N){ if (N == 0) return 1; // Recursive call return N * factorial(N - 1);}int main(){ int n; n = 13; factorial_iteration(n); n = 9; printf("Factorial of %d using recursion:%d\n", n, factorial(n)); return 0;}

// C program to check if number// is Armstrong number or not#include <stdio.h>// Function to calculate x raised to the power yint power(int x, unsigned int y){ if (y == 0) return 1; if (y % 2 == 0) return power(x, y / 2) * power(x, y / 2); return x * power(x, y / 2) * power(x, y / 2);}// Function to calculate order of the numberint order(int n){ int res = 0; while (n) { res++; n = n / 10; } return res;}// Function to check whether the given number is// Armstrong number or notint isArmstrong(int x){ // Calling order function int n = order(x); int temp = x, sum = 0; while (temp) { int r = temp % 10; sum += power(r, n); temp = temp / 10; } // If satisfies Armstrong condition if (sum == x) return 1; else return 0;}// Driver Programint main(){ int x = 120; if (isArmstrong(x) == 1) printf("True\n"); else printf("False\n"); x = 1634; if (isArmstrong(x) == 1) printf("True\n"); else printf("False\n"); return 0;}

// C program to find roots// of a quadratic equation#include <math.h>#include <stdio.h>#include <stdlib.h>// Prints roots of quadratic equation ax*2 + bx + xvoid find_roots(int a, int b, int c){ // If a is 0, then equation is not quadratic, but // linear if (a == 0) { printf("Invalid"); return; } int d = (b * b) - (4 * a * c); double sqrt_val = sqrt(abs(d)); if (d > 0) { printf("Roots are real and different \n"); printf("%f\n%f", (double)(-b + sqrt_val) / (2 * a), (double)(-b - sqrt_val) / (2 * a)); } else if (d == 0) { printf("Roots are real and same \n"); printf("%f", -(double)b / (2 * a)); } else // d < 0 { printf("Roots are complex \n"); printf("%f + i%f\n%f - i%f", -(double)b / (2 * a), sqrt_val / (2 * a), -(double)b / (2 * a), sqrt_val / (2 * a)); }}// Driver codeint main(){ int a = 1, b = -16, c = 1; // Function call find_roots(a, b, c); return 0;}

// C Programs to Calculate// reverse of a number#include <stdio.h>// Iterative approachint reverse_iteration(int N){ int ans = 0; while (N != 0) { ans = ans * 10 + (N % 10); N = N / 10; } return ans;}// recursive approachint reverse(int n, int ans){ if (n == 0) return ans; ans = ans * 10 + n % 10; return reverse(n / 10, ans);}int main(){ int N = 15942; printf("Initial number:%d\n", N); N = reverse_iteration(N); printf("%d after reverse using iteration\n", N); int ans = 0; ans = reverse(N, ans); printf("%d after again reverse using recursion", ans); return 0;}

// C Program for// Checking Palindrome#include <stdio.h>// Checking if the number is// Palindrome numbervoid check_palindrome(int N){ int T = N; int rev = 0; // This variable stored reversed digit // Execute a while loop to reverse digits of given // number while (T != 0) { rev = rev * 10 + T % 10; T = T / 10; } // Compare original_number with reversed number if (rev == N) printf("%d is palindrome\n", N); else printf("%d is not a palindrome\n", N);}int main(){ int N = 13431; int M = 12345; // Function call check_palindrome(N); check_palindrome(M); return 0;}

// C Program for checking numbers// are equal using bitwise operator#include <stdio.h>int main(){ int x = 1; int y = 2; // Using XOR // XOR of two equal numbers is 0 if (!(x ^ y)) printf(" %d is equal to %d ", x, y); else printf(" %d is not equal to %d ", x, y); return 0;}

// C program to find GCD of two numbers#include <math.h>#include <stdio.h>// Function to return gcd of a and bint gcd(int a, int b){ // Find Minimum of a and b int result = ((a < b) ? a : b); while (result > 0) { if (a % result == 0 && b % result == 0) { break; } result--; } return result; // return gcd of a and b}// Driver program to test above functionint main(){ int a = 98, b = 56; printf("GCD of %d and %d is %d ", a, b, gcd(a, b)); return 0;}

// C program to find// LCM of two numbers#include <stdio.h>// minimum of two numbersint Min(int Num1, int Num2){ if (Num1 >= Num2) return Num2; else return Num1;}int LCM(int Num1, int Num2, int K){ // If either of the two numbers // is 1, return their product if (Num1 == 1 || Num2 == 1) return Num1 * Num2; // If both the numbers are equal if (Num1 == Num2) return Num1; // If K is smaller than the // minimum of the two numbers if (K <= Min(Num1, Num2)) { // Checks if both numbers are // divisible by K or not if (Num1 % K == 0 && Num2 % K == 0) { // Recursively call LCM() function return K * LCM(Num1 / K, Num2 / K, 2); } // Otherwise else return LCM(Num1, Num2, K + 1); } // If K exceeds minimum else return Num1 * Num2;}int main(){ // Given N & M int N = 12, M = 9; // Function Call int ans = LCM(N, M, 2); printf("%d", ans); return 0;}

// C Program to check// Maximum and Minimum// Between two numbers// Without any condition or loop#include <stdio.h>#include <stdlib.h>int main(){ int a = 55, b = 23; // return maximum among the two numbers printf("max = %d\n", ((a + b) + abs(a - b)) / 2); // return minimum among the two numbers printf("min = %d", ((a + b) - abs(a - b)) / 2); return 0;}

// C program to print// all natural numbers// upto N without using semi-colon#include <stdio.h>#define N 10int main(int val){ if (val <= N && printf("%d ", val) && main(val + 1)) { }}

// C program to find area// of circle#include <math.h>#include <stdio.h>#define PI 3.142double findArea(int r) { return PI * pow(r, 2); }int main(){ printf("Area is %f", findArea(5)); return 0;}

// C Program print Pyramid pattern#include <stdio.h>int main(){ int N = 5; // Outer Loop for number of rows for (int i = 1; i <= N; i++) { // inner Loop for space printing for (int j = 1; j <= N - i; j++) printf(" "); // inner Loop for star printing for (int j = 1; j < 2 * i; j++) printf("*"); printf("\n"); } return 0;}

// C Program to print// Pascal's Triangle#include <stdio.h>int main(){ int n = 5;   for (int i = 1; i <= n; i++) { for (int j = 1; j <= n - i; j++) { printf(" "); } int x = 1; for (int j = 1; j <= i; j++) { printf("%d ", x); x = x * (i - j) / j; } printf("\n"); } return 0;}

// C program to return the Nth row of pascal's triangle#include <stdio.h>// Print the N-th row of the Pascal's Trianglevoid generateNthrow(int N){ // nC0 = 1 int prev = 1; printf("%d", prev); for (int i = 1; i <= N; i++) { // nCr = (nCr-1 * (n - r + 1))/r int curr = (prev * (N - i + 1)) / i; printf(",%d ", curr); prev = curr; }}int main(){ int n = 5; generateNthrow(n); return 0;}

// C Program to reverse// An array#include <stdio.h>void reverse(int* arr, int n){ // Swapping front and back elements. for (int i = 0, j = n - 1; i < j; i++, j--) { int ele = arr[i]; arr[i] = arr[j]; arr[j] = ele; }}int main(){ int arr[] = { 1, 2, 3, 4, 5 }; // Function Call reverse(arr, 5); // reverse array element printing for (int i = 0; i < 5; i++) printf("%d ", arr[i]); return 0;}

// C Program for// checking duplicate// values in a array#include <stdio.h>int Sort(int arr[], int size){ for (int i = 0; i < size - 1; i++) { for (int j = 0; j < size - i - 1; j++) { if (arr[j] > arr[j + 1]) { int temp = arr[j]; arr[j] = arr[j + 1]; arr[j + 1] = temp; } } }}// find repeating elementvoid findRepeating(int arr[], int n){ int count = 0; for (int i = 0; i < n; i++) { int flag = 0; while (i < n - 1 && arr[i] == arr[i + 1]) { flag = 1; i++; } if (flag) printf("%d ", (arr[i - 1])); } return;}int main(){ int arr[] = { 1, 3, 4, 1, 2, 3, 5, 5 }; int n = sizeof(arr) / sizeof(arr[0]);  Sort(arr,n);  findRepeating(arr,n);   return 0;}

// C Program for calculating// maximum and minimum element#include <stdio.h>void find_small_large(int arr[], int n){ int min, max; // assign first element as minimum and maximum min = arr[0]; max = arr[0]; for (int i = 1; i < n; i++) { // finding smallest here if (arr[i] < min) min = arr[i]; // finding largest here if (arr[i] > max) max = arr[i]; } printf("Maximum: %d and Minimum: %d\n", min, max);}int main(){ int arr[] = { 15, 14, 35, 2, 11, 83 }; int len = sizeof(arr) / sizeof(arr[0]); // Function call find_small_large(arr, len); return 0;}

// C program to rotate// Array by k elements#include <stdio.h>// Print arrayvoid printArray(int arr[], int n){ int i; for (i = 0; i < n; i++) printf("%d ", arr[i]);}// Caculates greatest common divisorint gcd(int a, int b){ if (b == 0) return a; else return gcd(b, a % b);}// Rotate arrayvoid Rotate(int arr[], int k, int N){ int i, j, a, temp; k = k % N; int rotate = gcd(k, N); for (i = 0; i < rotate; i++) { temp = arr[i]; j = i; while (1) { a = j + k; if (a >= N) a = a - N; if (a == i) break; arr[j] = arr[a]; j = a; } arr[j] = temp; }}int main(){ int arr[] = { 1, 2, 3, 4, 5 }; // Rotating array Rotate(arr, 2, 5); // Printing array printArray(arr, 5); return 0;}

// C Program for Sorting// First half in Ascending order// and Second Descending order#include <stdio.h>void Sort_asc_desc(int arr[], int n){ int temp; for (int i = 0; i < n - 1; i++) { for (int j = i + 1; j < n; j++) { if (arr[i] > arr[j]) { temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; } } } // printing first half in ascending order for (int i = 0; i < n / 2; i++) printf("%d ", arr[i]); // printing second half in descending order for (int j = n - 1; j >= n / 2; j--) printf("%d ", arr[j]);}int main(){ int arr[] = { 11, 23, 42, 16, 83, 73, 59 }; int N = sizeof(arr) / sizeof(arr[0]); Sort_asc_desc(arr, N); return 0;}

// C Program to print sum of// all subsets#include <stdio.h>// Function to print sum of subset// Using recursionvoid subset_sum(int arr[], int i, int j, int sum){ if (i > j) { printf("%d ", sum); return; } subset_sum(arr, i + 1, j, sum + arr[i]); subset_sum(arr, i + 1, j, sum);}// driver codeint main(){ int arr[] = { 1, 2, 3 }; int n = sizeof(arr) / sizeof(arr[0]); // Function calling to print subset sum subset_sum(arr, 0, n - 1, 0); return 0;}

// C Program to check 0 sum// subarray possible#include <stdio.h>int main(){ // array int arr[] = { -2, 2, 1, 1, 8 }; int n = sizeof(arr) / sizeof(arr[0]); int flag = 0, sum; // Traversing array to check for (int i = 0; i < n; i++) { for (int j = i; j < n; j++) { sum += arr[j]; if (sum == 0) { flag = 1; printf( "True subarray with 0 sum is possible"); break; } } } if (flag == 0) printf("No such condition");}

// C program to implement Kadane's Algorithm#include <limits.h>#include <stdio.h>int main(){ int a[] = { -2, -3, 4, -1, -2, 1, 5, -3 }; int n = sizeof(a) / sizeof(a[0]); int max_so_far = INT_MIN, max_ending_here = 0, start = 0, end = 0, s = 0; for (int i = 0; i < n; i++) { max_ending_here += a[i]; if (max_so_far < max_ending_here) { max_so_far = max_ending_here; start = s; end = i; } if (max_ending_here < 0) { max_ending_here = 0; s = i + 1; } } printf("Maximum contiguous sum is %d\n", max_so_far); printf("Starting index %d Ending index %d", start, end);  return 0;}

#include <stdio.h>// This function stores transpose of A[][] in B[][]void transpose(int N, int M, int A[M][N], int B[N][M]){ int i, j; for (i = 0; i < N; i++) for (j = 0; j < M; j++) B[i][j] = A[j][i];}int main(){ int M = 3; int N = 4;  int A[3][4] = { { 1, 1, 1, 1 }, { 2, 2, 2, 2 }, { 3, 3, 3, 3 } }; // Note dimensions of B[][] int B[N][M], i, j; transpose(N, M, A, B); printf("Result matrix is \n"); for (i = 0; i < N; i++) { for (j = 0; j < M; j++) printf("%d ", B[i][j]); printf("\n"); } return 0;}

// C Program to rotate the array// By 90 degree in clockwise direction#include <stdio.h>void swap(int* a, int* b){ int temp = *a; *a = *b; *b = temp;}int main(){ int n = 4; int arr[4][4] = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 }, { 13, 14, 15, 16 } }; // Print Orignal Matrix printf("Orignal Matrix:\n"); for (int i = 0; i < n; i++) { for (int j = 0; j < n; j++) { printf("%d ", arr[i][j]); } printf("\n"); } // Rotate the matrix about the main diagonal for (int i = 0; i < n; i++) { for (int j = 0; j < i; j++) swap(&arr[i][j], &arr[j][i]); } // Rotate the matrix about middle column for (int i = 0; i < n; i++) { for (int j = 0; j < n / 2; j++) { swap(&arr[i][j], &arr[i][n - j - 1]); } } // Print the rotated matrix printf("Matrix after rotation: \n"); for (int i = 0; i < n; i++) { for (int j = 0; j < n; j++) { printf("%d ", arr[i][j]); } printf("\n"); }}

// C Program to find Spiral Traversal// Of a matrix#include <stdio.h>int main(){ int arr[4][4] = { { 1, 5, 9, 13 }, { 2, 6, 10, 14 }, { 3, 7, 11, 15 }, { 4, 8, 12, 16 } }; int m = 4, n = 4; int i, l = 0, right = m - 1, begin = 0, end = n - 1; while (l <= right && begin <= end) { // Print the first row // from the remaining rows for (i = l; i <= right; ++i) { printf("%d ", arr[begin][i]); } begin++; // Print the last column // from the remaining columns for (i = begin; i <= end; ++i) { printf("%d ", arr[i][right]); } right--; // Print the last row from // the remaining rows if (begin <= end) { for (i = right; i >= l; --i) { printf("%d ", arr[end][i]); } end--; } // Print the first column from // the remaining columns if (l <= right) { for (i = end; i >= begin; --i) { printf("%d ", arr[i][l]); } l++; } } return 0;}

#include <stdio.h>int main(){ char s[] = "124259"; int ans = 0; // iterate through all the number for (int i = 0; s[i] != '\0'; i++) { int ele = s[i] - 48; if (ele <= 9) ans += ele; }  // print sum of the numbers printf("%d", ans); return 0;}

// C Program to calculate// length of a string#include <stdio.h>#include <string.h>int length(char s[], int i){ if (s[i] == '\0') return 0; return length(s, i + 1) + 1;}int main(){ char s[] = "GeeksforGeeks"; // Calculating using strlen int len = strlen(s); printf("length using strlen:%d\n", len); // Calculating using iteration int i; for (i = 0; s[i] != '\0'; i++) { continue; } printf("length using iteration:%d\n", i); // Calculating using recursion int ans = length(s, 0); printf("length using recursion:%d\n", ans); return 0;}

// C implementation to check if a given// string is palindrome or not#include <stdio.h>#include <string.h>#include <stdbool.h>bool is_palindrome(char* str, int i, int j){ if (i >= j) { return true; } if (str[i] != str[j]) { return false; } return is_palindrome(str, i + 1, j - 1);}void check_palindrome(char* str){ // Start from leftmost and // rightmost corners of str int h = 0; int flag = 0; int l = strlen(str) - 1; // Keep comparing characters // while they are same while (h > l) { if (str[l++] != str[h--]) { printf("%s is not a palindrome\n", str); flag = 1; break; // will break from here } } if (flag == 0) printf("%s is a palindrome\n", str);}int main(){ char str[] = { "GeekeeG" }; char str2[] = { "GeeksforGeeks" }; check_palindrome(str); printf("Checking %s using recursive approach\n", str2); bool ans = is_palindrome(str2,0,strlen(str2)-1); if (ans) printf("It is Palindrome\n"); else printf("Not a Palindrome\n"); return 0;}

// C Program to print all permutations of a string in sorted// order.#include <stdio.h>#include <stdlib.h>#include <string.h>// function two compare two characters a and bint compare(const void* a, const void* b){ return (*(char*)a - *(char*)b);}// function two swap two characters a and bvoid swap(char* a, char* b){ char t = *a; *a = *b; *b = t;}// function finds the index of the smallest characterint findCeil(char str[], char first, int l, int h){ int ceilIndex = l; for (int i = l + 1; i <= h; i++) if (str[i] > first && str[i] < str[ceilIndex]) ceilIndex = i; return ceilIndex;}// Print all permutations of str in sorted ordervoid sortedPermutations(char str[]){ int size = strlen(str); qsort(str, size, sizeof(str[0]), compare); int isFinished = 0; while (!isFinished) { printf("%s \n", str); int i; for (i = size - 2; i >= 0; --i) if (str[i] < str[i + 1]) break; if (i == -1) isFinished = 1; else { int ceilIndex = findCeil(str, str[i], i + 1, size - 1); swap(&str[i], &str[ceilIndex]); qsort(str + i + 1, size - i - 1, sizeof(str[0]), compare); } }}int main(){ char str[] = "123"; sortedPermutations(str); return 0;}

// C program to calculate the Power of a Number using// Recursion#include <stdio.h>int power(int a, int b){ if (b == 0) return 1; return power(a, b - 1) * a;}int main(){ int a = 4, b = 5; int ans = power(a, b); printf("%d", ans); return 0;}