Functions

[Baljeet]

Functions

A function is a way of encapsulating code for reuse. The proper use of functions can make modifying your code much easier.

A Basic Function

void out(int v) {
	v++;
	cout << v << endl;
}

You call this function like this:

out(6);

Output:



Now, whenever you want to output an integer. All you need to do is call the out function and pass the integer.

When you declare a function you use this syntax:

return type name(parameters) {
body
}

Arrays by Reference? Passing Arrays

When you pass parameters they are passed by copy. However, arrays and objects are a little different. When you pass an array to a function, you pass the memory address of the array to the function. This is how it appears to be passed by reference.


Passing by reference

void update(int& v) {
 	v++;
}

int main() {
	int v = 5;
	update(v);
	cout << v << endl;

	return 0;
}

Output:

6

When you want things updated in the function, passing by reference is useful. You might want this behaviour when you are sorting arrays.

Example:

void sort(int v[], int size) {
	for (int i=0;i<size-1;i++) {
		for (int x=i+1;x<size;x++) {
			if (v[x] < v[i]) {
				v[x] ^= v[i];
				v[i] ^= v[x];
			}
		}
	}
}

int arn[] = {4,3,2,5,1,7};

sort(arn,6);

    for (int i=0;i<6;i++) {
        cout << arn[i] << " ";
    }
    cout << endl;

Even though, the function is not indicating the array is being passed by reference, it is being passed by a reference as you can tell when you look at the output. The array has been sorted.

Output:



Constant parameters

Passing a value as a constant ensures that you can never modify the variable in the function.

This might be useful in a search function.

Example:

int search(const int v[], int size, int target) {
    for (int i=0;i<size;i++) {
        if (v[i] == target) {
                return i;
        }
    }
    return -1;
}

This code returns i which is the index of the target in the array or -1 if it is not found.

If I try to modify v in the function, I get an error saying trying to modify a read only parameter.

Return values

All methods return a value which is indicated with a return statement. There may be several return statements in a function but a function can onyl return 1 value. Unless the function is a void function in which case it does not return any value.

Recursive functions

A function that calls itself is said to be a recursive function. These are complicated beasts and are a topic for their own tutorial.

Example:

int fib(int n) {
        if (n <= 1) return n;
        return fib(n-1) + fib(n-2);
}

All Credits goes to one who really made this...