C Functions

User-defined Functions: Functions in C are blocks of code designed to perform a particular task. User-defined functions help organize and reuse code by breaking programs into smaller modules.

Types of Functions: Built-in functions (like printf(), scanf()) and User-defined functions (created by programmers).

Return Types: Functions can return different data types like int, float, char, or void (no return).

1. void sum() - No parameters, no return

#include <stdio.h>

void sum() {
  int a = 5, b = 10;
  printf("Sum = %d\n", a + b);
}

int main() {
  sum();
  return 0;
}

Output: Sum = 15

This function prints sum of 5 and 10. No input parameters, no return.

2. void sum(int a, int b) - Parameters, no return

#include <stdio.h>

void sum(int a, int b) {
  printf("Sum = %d\n", a + b);
}

int main() {
  sum(7, 8);
  return 0;
}

Output: Sum = 15

Function takes two inputs and prints their sum, but does not return any value.

3. int sum() - No parameters, returns int

#include <stdio.h>

int sum() {
  int a = 3, b = 4;
  return a + b;
}

int main() {
  int result = sum();
  printf("Sum = %d\n", result);
  return 0;
}

Output: Sum = 7

Function returns the sum of two fixed numbers.

4. int sum(int a, int b) - Parameters and returns int

#include <stdio.h>

int sum(int a, int b) {
  return a + b;
}

int main() {
  int result = sum(12, 13);
  printf("Sum = %d\n", result);
  return 0;
}

Output: Sum = 25

Function adds two inputs and returns the sum.

5. Function to calculate percentage (no params, returns float)

#include <stdio.h>

float calculatePercentage() {
  int total = 500;
  int obtained = 425;
  return (obtained * 100.0) / total;
}

int main() {
  float percent = calculatePercentage();
  printf("Percentage = %.2f%%\n", percent);
  return 0;
}

Output: Percentage = 85.00%

Calculates percentage of obtained marks out of total.

6. Function with parameters and return float (percentage calculation)

#include <stdio.h>

float calculatePercentage(int total, int obtained) {
  return (obtained * 100.0) / total;
}

int main() {
  int total, obtained;
  printf("Enter total marks: ");
  scanf("%d", &total);
  printf("Enter obtained marks: ");
  scanf("%d", &obtained);

  float percent = calculatePercentage(total, obtained);
  printf("Percentage = %.2f%%\n", percent);
  return 0;
}

Output (example input):

Enter total marks: 600
Enter obtained marks: 480
Percentage = 80.00%

Calculates percentage based on user input using function with parameters.

7. void function with scanf()

#include <stdio.h>

void greetUser() {
  char name[50];
  printf("Enter your name: ");
  scanf("%49s", name);
  printf("Hello, %s!\n", name);
}

int main() {
  greetUser();
  return 0;
}

Output (example input):

Enter your name: Aryan
Hello, Aryan!

Function asks for user input and greets by name.

8. Function returning character

#include <stdio.h>

char getGrade(int marks) {
  if (marks >= 90) return 'A';
  else if (marks >= 75) return 'B';
  else if (marks >= 60) return 'C';
  else return 'F';
}

int main() {
  int score = 85;
  char grade = getGrade(score);
  printf("Grade: %c\n", grade);
  return 0;
}

Output: Grade: B

Returns grade based on marks.

9. Recursive function to calculate factorial

#include <stdio.h>

int factorial(int n) {
  if (n == 0) return 1;
  else return n * factorial(n - 1);
}

int main() {
  int num = 5;
  printf("Factorial of %d is %d\n", num, factorial(num));
  return 0;
}

Output: Factorial of 5 is 120

Calculates factorial recursively.

10. Function with default parameter behavior (simulate)

#include <stdio.h>

int multiply(int a, int b) {
  return a * b;
}

int multiplyDefault(int a) {
  return multiply(a, 2); // default b=2
}

int main() {
  printf("Multiply 5 * 3 = %d\n", multiply(5, 3));
  printf("Multiply 5 * default(2) = %d\n", multiplyDefault(5));
  return 0;
}

Output:

Multiply 5 * 3 = 15
Multiply 5 * default(2) = 10

Simulates default parameter by calling function with fixed value.

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