cpp functions

Functions improves a program by modularizing it and allowing code to be reused. 3 steps:

1. Declare the function - The functions should be declared at the top or it should be defined at the top
2. Define the function - The declared function should be defined. Please note the the arguments and the return datatype should match.
3. Call the function.

The following program gives an example of a function that take two double value. The function does not return any value therefore it is declared as void.

#include <iostream>
using namespace std;
void findSum(double, double); //1. Declare the function

int main() {

	double num1, num2;
	cout << "Enter first number : ";
	cin >> num1;
	cout << "Enter second number : ";
	cin >> num2;
	findSum(num1, num2); //3. Call the function
	return 0;
}

void findSum(double i, double j) { //2. Define the function
	double result;
	result = i + j;
	cout << "The sum is : " << result << endl;
}

The following program gives an example of two functions. Both functions return a value.

#include <iostream>
using namespace std;
double findSum(double, double); //1. Declare the function
double findProduct(double, double);
int main() {
	double num1, num2, result;
	cout << "Enter first number : ";
	cin >> num1;
	cout << "Enter second number : ";
	cin >> num2;
	result = findSum(num1, num2); //3. Call the function
	cout << "The sum is : " << result << endl;
	cout << "The product is : " << findProduct(num1, num2) << endl;
	return 0;
}
double findSum(double i, double j) { //2. Define the function
	double r;
	r = i + j;
	return r;
}
double findProduct(double i, double j) { //2. Define the function
	double r;
	r = i * j;
	return r;
}

The following example shows default argument for the power function. Note that the power function declaration specifies a default value for the second argument. The power function will work with one or two arguments.

#include <iostream>
using namespace std;
double findSum(double, double); //1. Declare the function
double findProduct(double, double);
int power(int, int = 2);
int main() {
	double num1, num2, result;
	cout << "Enter first number : ";
	cin >> num1;
	cout << "Enter second number : ";
	cin >> num2;
	result = findSum(num1, num2); //3. Call the function
	cout << "The sum is : " << result << endl;
	cout << "The product is : " << findProduct(num1, num2) << endl;
	cout << num1 << " raised to the power " << num2 << " is : " << power(num1, num2) << endl; 
	cout << num1 << " raised to the power of 2 is : " << power(num1) << endl;
	return 0;
}
double findSum(double i, double j) { //2. Define the function
	double r;
	r = i + j;
	return r;
}
double findProduct(double i, double j) { //2. Define the function
	double r;
	r = i * j;
	return r;
}
int power(int b, int p) { //2. Define the function
	return pow(b, p);
}

Another example:

#include <iostream>
using namespace std;
void max(double, double); //Declare Function
double min(double, double); //Declare Function
double sum(double, double);
double average(double, double);
int main(){
	double num1, num2, result;
	cout << "Enter the first number: ";
    cin >> num1;
    cout << "Enter the second number: ";
    cin >> num2;
    max(num1, num2); //call the function
	result = min(num1, num2);
	cout << "Min: " << result << endl;
    cout << "Sum: " << sum(num1, num2) << endl;
    cout << "Average: " << average(num1, num2) << endl;
    return 0;
}
void max(double a, double b) { //Define
	if (a > b)
    	cout << "Max: " << a << endl;
    else
		cout << "Max: " << b << endl;
}
double min(double a, double b) { //Define
	if (a < b)	
    	return a;
	else
		return b;
}
double sum(double a, double b) { //Define
	return a + b;
}
double average(double a, double b) { //Define
	return (a + b)/2;
}