functions.md

Functions

Function: a function is a block of code that can return a value and that can be called wherever it is needed.

Example:

void birthday() { // void is the data type of the return value, since we don't have a return value here, we use a void
	printf("Happy birthday to you!\n");
	printf("Happy birthday to you!\n");
	printf("Happy birthday dear you!\n");
	printf("Happy birthday to you!\n");
}

int main() {
	birthday(); // -> Happy birthday to you!
		    //    Happy birthday to you!
		    //    Happy birthday dear you!
		    //    Happy birthday to you!
	return 0;
}

Function arguments

Functions can take in variables called arguments to be used inside of itself.

Example:

void birthday(char s[], int x) { // the birthday function takes in two arguments: s (of type char) and x (of type int)
	printf("Happy birthday, dear %s!\n", s);
	printf("You are %d years old!\n", n);
}

int main() {
	char name[] = "DarkblooM";
	int age = 21;
	birthday(name, age); // -> Happy birthday, dear DarkblooM!
			     //    You are 21 years old! 
	return 0;
}

Return statement

The return statement returns a value back to a calling function.

Example:

double square(double x) { // this function expects to return a double
	double result = x * x;
	return result;    // returning a double as expected by the function type indicated earlier
}

int main() {
	double n = square(3.14);
	printf("%lf", n); // -> 9.859600
	return 0;
}

Ternary operators

Ternary operators behave as shortcuts to if/else statements when assigning or returning a value.

Example:

int findMax(int x, int y) {
	return (x > y) ? x : y; // if x > y (?), then return x, else (:) return y
}

int main() {
	int max = findMax(3, 4);
	printf("%d", max);      // -> 4
}

Function prototypes

Prototyping a function is essentially declaring it without a body before main() to ensure that calls to said function are made with the correct arguments.

Example:

void hello(char name, int age);    // function prototype

int main() {
	char name[] = "DarkblooM";
	int age = 20;
	hello(name, age);          // -> Hello DarkblooM
			           //    You are 20 years old
	return 0;
}

void hello(char name[], int age) { // function with body
	printf("Hello %s\n", name);
	printf("You are %d years old\n", age);
}

Many C compilers do not check for parameter matching, missing arguments will result in unexpected behavior. A function prototype causes the compiler to flag an error if arguments are missing.