Functions

Function declaration and definition

int main(void) {
  printf("Hello World!\n");

  return 0;
}

The function consists of two parts

void myFunction() { // declaration declaration
  // function body (code to be executed) (definition)
}

---

• Declaration declares the function name, return type and parameters (if any)
• Definition function body (code to execute)

---

// function declaration
void myFunction();
// main method
int main() {
  myFunction(); // --> call the function

  return 0;
}

void myFunction() {// Function definition
  printf("Good evening!\n");
}

Call function

// create function
void myFunction() {
  printf("Good evening!\n");
}

int main() {
  myFunction(); // call the function
  myFunction(); // can be called multiple times

  return 0;
}
// Output -> "Good evening!"
// Output -> "Good evening!"

Function parameters

void myFunction(char name[]) {
  printf("Hello %s\n", name);
}

int main() {
  myFunction("Liam");
  myFunction("Jenny");

  return 0;
}
// Hello Liam
// Hello Jenny

Multiple parameters

void myFunction(char name[], int age) {
  printf("Hi %s, you are %d years old.\n",name,age);
}
int main() {
  myFunction("Liam", 3);
  myFunction("Jenny", 14);

  return 0;
}
// Hi Liam you are 3 years old.
// Hi Jenny you are 14 years old.

Return value

int myFunction(int x) {
  return 5 + x;
}

int main() {
  printf("Result: %d\n", myFunction(3));
  return 0;
}
// output 8 (5 + 3)

Two parameters

int myFunction(int x, int y) {
  return x + y;
}

int main() {
  printf("Result: %d\n", myFunction(5, 3));
  // store the result in a variable
  int result = myFunction(5, 3);
  printf("Result = %d\n", result);

  return 0;
}
// result: 8 (5 + 3)
// result = 8 (5 + 3)

Recursive example

int sum(int k);

int main() {
  int result = sum(10);
  printf("%d\n", result);

  return 0;
}

int sum(int k) {
  if (k > 0) {
    return k + sum(k -1);
  } else {
    return 0;
  }
}

Mathematical functions

#include <math.h>

void main(void) {
  printf("%f\n", sqrt(16)); // square root
  printf("%f\n", ceil(1.4)); // round up (round)
  printf("%f\n", floor(1.4)); // round down (round)
  printf("%f\n", pow(4, 3)); // x(4) to the power of y(3)
}

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• abs(x) absolute value
• acos(x) arc cosine value
• asin(x) arc sine
• atan(x) arc tangent
• cbrt(x) cube root
• cos(x) cosine
• the value of exp(x) Ex
• sin(x) the sine of x
• tangent of tan(x) angle

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