# Functions 1:

## Structure of Function

## Syntax

For eg: Write a function that returns the factorial of given number.

Code :

int factorial (int N){
    int ans = 1;
    for(int i = 1; i <= N; i++){
        ans = ans*i;
    }
    return ans;
}

In order to get some result just creating the function is not enough, we need to use the function.

### Syntax 1: In order to use the function, we need to call it.
Code:

function_name(input);

### Syntax 2: When function is returning something, we need to either print or store the function call to see the output.

Code:

static int factorial (int N){
    int ans = 1;
    for(int i = 1; i <= N; i++){
        ans = ans*i;
    }
    return ans;
}

public static void main(String args[]) {
    factorial(5);
}

Output:

Explanation:

We are not getting any output because even though we are receiving 120 from our factorial function, we are not printing it.

Code:

static int factorial (int N){
    int ans = 1;
    for(int i = 1; i <= N; i++){
        ans = ans*i;
    }
    return ans;
}

public static void main(String args[]) {
    int x = factorial(5);
    System.out.println(x);
}

Output:

120

Explanation:

We are receiving 120 from our factorial function in out function call and then we are assigning this value to variable x and printing the value of x.

Code:

static int factorial (int N){
    int ans = 1;
    for(int i = 1; i <= N; i++){
        ans = ans*i;
    }
    return ans;
}

public static void main(String args[]) {
    System.out.println(factorial(5));
}

Output:

120

Explanation:

We are receiving 120 from our factorial function in our function call and we are printing it.

### Syntax 3: When we have more than one input parameter we seprate them by comma ( , )

For eg: Write a function that returns the sum of two numbers.

Code:

int addition(int x, int y){
    int ans = x + y;
    return ans;
}

### Syntax 4: When the function is not returning anything, the return type is void

For eg: Write a function that prints the max of two numbers.

Code:

void maxOfTwo(int a, int b){
    if(a > b){
        System.out.println(a);
    }
    else{
        System.out.println(b);        
    }
}

### Syntax 5: When the return type is void, We can neither print the function call nor store it

Code 1:

static void maxOfTwo(int a, int b){
    if(a > b){
        System.out.println(a);
    }
    else{
        System.out.println(b);        
    }
}
public static void main(String[] args){
    System.out.println(maxOfTwo(19, 36));
}

Output:

Error: 'void' type not allowed here
		System.out.println(maxOfTwo(19,36));
		                           ^
1 error                                   

Code 2:

static void maxOfTwo(int a, int b){
    if(a > b){
        System.out.println(a);
    }
    else{
        System.out.println(b);        
    }
}
public static void main(String[] args){
    int ans = maxOfTwo(19, 36);
    System.out.println(ans);
}

Output:

Error: incompatible types: void cannot be converted to int
		int ans = maxOfTwo(19, 36);
		                  ^
1 error

## Predefined functions
These are built – in functions in Java, which are instantly available to use in your program.

Things to keep in mind while using predefined functions:
1. Check number of parameters required in the function
2. Check the return type of the function

Java Math functions List : [Link](https://www.w3schools.com/java/java_ref_math.asp)

Code:

public static void main(String[] args){
    int x1 = Math.max(51, 90);
    System.out.println(x1);
    int x2 = Math.min(51, 90);
    System.out.println(x2);
    double x3 = Math.pow(3, 4);
    System.out.println(x3);
}

Output:

90
51
81

Explanation:

Math.max(a,b) gives the bigger value between a and b
Math.min(a,b) gives the smaller value between a and b
Math.pow(a,b) gives a^b as output