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Functions and Recursion in C
//Basic Syntax
#include<stdio.h>
void add() { int a,b,c; scanf("%d",&a); scanf("%d",&b); c=a+b; return c; } int main() { printf("%d",add()); return 0; }
//Functions
A function is a block of code that performs a specific task. It allows us to divide a large program into smaller, manageable parts.
//Syntax of a Function
return_type function_name(parameter_list) { // Function body return value; // (if return type is not void) }
//Example of a Function
#include <stdio.h> // Function declaration int add(int, int); int main() { int a = 5 , b = 10 ; int result = add(a, b); // Function calling printf("Sum = %d\n", result); return 0 ; } // Function definition int add(int x, int y) { return x + y;
//Types of Functions Based on Arguments and Return Type
Type Arguments Return Type Example Function with return & arguments Yes Yes int add(int, int); Function with return, no arguments No Yes int getValue(); Function with arguments, no return Yes No void printValue(int); Function with no return & no arguments No No void display();
//Recursion
Recursion is a technique where a function calls itself directly or indirectly to solve a problem.
//Properties of Recursion
- Base Condition – A condition to stop recursion.
- Recursive Case – A part where the function calls itself.
//Example: Factorial Using Recursion
#include <stdio.h> // Function to calculate factorial int factorial(int n) { if (n == 0 ) // Base Condition return 1 ; return n * factorial(n - 1 ); // Recursive Call } int main() { int num = 5 ; printf("Factorial of %d = %d\n", num, factorial(num)); return 0 ; }
//Types of Recursion
- Direct Recursion – A function directly calls itself.
- Indirect Recursion – Function A calls Function B, which in turn calls Function A.
// Validating input if (r > num || num < 0 || r < 0) { printf("Invalid input! Ensure that n >= r >= 0.\n"); } else { printf("P(%d, %d) = %lld\n", num, r, permutations(num, r)); } return 0; }
circular prime
#include <stdio.h> #include <math.h> int is_prime(int n) { if (n < 2) { return 0; // Numbers < 2 are not prime } for (int i = 2; i <= sqrt(n); i++) { // Corrected loop if (n % i == 0) { return 0; // Not prime } } return 1; // Prime } int main() { int num, temp, l, f, rot; printf("Enter number: "); scanf("%d", &num); int d = log10(num) + 1; // Get number of digits temp = num; // Preserve original number for (int i = 0; i < d; i++) { // Rotate based on digit count f = temp / 10; // Remove last digit l = temp % 10; // Extract last digit rot = (l * pow(10, d - 1)) + f; // Shift last digit to front if (!is_prime(rot)) { // Check if rotation is prime printf("not circular\n"); return 0; } temp = rot; // Update temp to new rotation
printf("circular\n"); return 0; }
Sum of odd numbers in an array using recursion
Way 1
#include <stdio.h> // Recursive function to sum odd numbers in the array int sumOdd(int arr[], int n) { if (n == 0) return 0; int lastElement = arr[n - 1]; // Get the last element return (lastElement % 2 != 0? lastElement : 0) + sumOdd(arr, n - 1); } int main() { int n; // Get the size of the array printf("Enter the number of elements: "); scanf("%d", &n); int arr[n]; // Input elements printf("Enter %d elements: ", n); for (int i = 0; i < n; i++) { scanf("%d", &arr[i]); } // Call the recursive function int sum = sumOdd(arr, n); // Output result printf("Sum of odd numbers: %d\n", sum); return 0;
