Functions 2¶

Agenda¶

Function Examples
Given N return sum of all even number
Given radius find area of circle
Even or odd
Given M check if it is a perfect square

Problem 1

Given N find and return sum of all even numbers till N ?

Example 1

 N = 10

Solution

N = 10
Even numbers less than equal to 10
2 -> 4 -> 6 -> 8 -> 10
adding 2 + 4 + 6 + 8 + 10 = 30

Example 2

 N = 5

Solution

N = 5
Even numbers less than equal to 5
2 -> 4
adding 2 + 4 = 6

Approach

Iterate from 2 to N with an increament of 2 in each step of iteration
Add the values obtained in each iteration.

static int evenSum(int N){
    int sum = 0;
    for(int i = 2 ;i <= N ; i += 2){
        sum += i;
    }
  return sum;
}

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int sum = evenSum(N);
    System.out.println(sum);
}

Dry run

 N = 7


Step	i	i<=N	Sum=sum+i	i=i+2
1	2	Yes	0+2=2	4
2	4	Yes	2+4=6	6
3	6	Yes	6+6=12	8
4	8	No

Problem 2

Given R (radius of the circle) find area of the circle

Approach

Calculate area using formula π*r2
But do we know the exact value of π ?
We might think it to be 3.14 but it is just an approximation.
therefore we will use the value of π using Math.PI in java.

Code

static double areaOfCircle(int R) {
  double area = Math.PI * R * R;
  return area;
}
public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int radius = scanner.nextInt();
  double circleArea = areaOfCircle(radius);
  System.out.println(circleArea);
}

Function Rules

When will a function end?
- When all lines are executed.
- We execute return statement in function.
What will happen a function ends ?
- What will happen a function ends ?
- We will go back to line from where it was called

Question¶

What will be the output?

public static void test1(){
  System.out.println("Hi");
  System.out.println("Welcome");
}
public static void main(){
  test1();
  System.out.println("Home");
}

Choices¶

Hi
Welcome
Home
Welcome
Home
Hi
Home
Welcome
Hi

Explanation

According to rule main() is executed and first test1() gets called.
Inside test1 there is no return statement since it is void. test ends after executing all lines of code so Hi and Welcome are printed.
after test1 ends we go back again in main() and Home is printed

Question¶

What will be the output?

public static void test2(){
  System.out.println("Hi");
  return;
}
public static void main(){
  test2();
  System.out.println("Hello");
}

Choices¶

Hi
Hello
Hello
Hi
Error

Explaination

Some people might answer Error because of return statement in void type function But will it actually produce an error ?
Since return statement is not returning any thing it won't produce an error.

Question

What will be the output?

public static boolean isEven(int N){
    if(N % 2 == 0){
      return true;
    }else{
      return false;
    }
}
public static void main(){
    System.out.println(isEven(60));
    System.out.println("Hello");
}

Choices¶

true
Hello
Hello
false
false
Hello

Explaination

We are calling isEven function with n = 60. So on entering the function we check for if n%2 == 0
Since 60 % 2==0 it enters if statement and returns true and isEven execution ends here
After that Hello is printed

Question¶

What will be the output?

public static boolean EvenOdd(int N){
  if(N % 2 == 0){
    System.out.println("Even");
     return;
  }
  System.out.print("Odd");
}
public static void main(){
  EvenOdd(10);
  System.out.println("Hello");
}

Choices¶

Even
Hello
Odd Hello
Hello

Explanation

We are calling EvenOdd function with N = 10 So on entering function the we check for if N%2 == 0
Since 10 % 2 ==0 it enters if statement an prints Even and due to return statement EvenOdd execution ends.
After that Hello is printed.

Question¶

What will be the output?

public static int check(int N){
  System.out.print(N+10);
}
public static void main(){
  check(15);
}

Choices¶

15
Error
No output

Explanation

When we run the function we get an ERROR : Missing return statement in function

Note : If any function having return type other then void then should have atleast one return statement.

Question¶

What will br the output?

public static int even(int n){
    if(n % 2 == 0){
      return 2;
    }
}
public static void main(){
    int a = even(10);
    System.out.print(a);
}

Choices¶

Even
Error
2

Explanation

When we run the function we get an ERROR : Missing return statement in function
This occurred because compiler checks if the condition is false then is there any return statement. Since there is no return statement Error is thrown.
If you create a function and there is a mistake in it. It doesn't weather you call it or not you will get an error
If you create a function and there is a mistake in it. It doesn't weather you call it or not you will get an error
If any function having return type other then void then should have return statements for all cases.
If any function having return type other then void then should have return statements for all cases.
So According to rules if we add return statement after if we can resolve the error

Question¶

What will be the output?

public static int test(int n){
    if(n % 2 == 0){
      return 2;
    }
    if(n % 5 == 0){
      return 5;
    }
}
public static void main(){
    int a = test(15);
}

Choices¶

5
Error
2
No output

Explanation

When we run the function we get an ERROR : Missing return statement in function.
This occurred because compiler checks if the first condition is false then is there any return statement.
Compiler checks if the second condition is false then is there any return statement.
Since there is no return statement Error is thrown.

Problem 3¶

Given N return true if the number is perfect square else return false?

N is said to be a perfect square if it can be expresses as product of two equal positive numbers.

Testcases

Idea

Starting from 1 (Smallest +ve number) check if there is any number p that satisfies the condition p*p == N

Example 1

Example 2

Observations

We can observe from above examples that :-
- We need to iterate starting from i=1
- We need iterate till i*i <= N
- On each iteration we check if i_i == N if so then return true else we return false.

Code

static boolean isPerfectSquare(int N){
   int i = 1;
   while(i * i <= N){
       if(i * i == N){
          return true;
       }
       i ++ ;
   }
    return false;
}
public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    System.out.println(isPerfectSquare(N));
}

Problem 4

Given N find the sum of all factor of N ?

Testcases

Observations & Approach

All factors of a number lies in range [1,N].
We iterate over range [1,N] and if a number is an factor we add it to the answer.

Code

static int sumOfFactors(int N){
  int ans = 0;
  for(int i = 1;i <= N;i ++ ){
    if(N % i == 0){
      ans += i;
    }
  }
return ans;
}
public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int N = scanner.nextInt();
  System.out.println(sumOfFactors(N));
}

Question¶

What will be the output?

public static int sum(int a, int b){
  return a+b;
  System.out.println("Hey");
}
public static void main(){
  int x = 10, y = 20;
  System.out.pritnln(sum(x,y));
}

Choices¶

Error
30
Hey

Explanation

Here error is generated because of print command just after return in function sum
The code after return can not be executed still compiler sees valid statements(not commented lines) and hence throws unreachable statement error
Statements after return are not executed. If there are statements after return then compiler throws error → [Statement Unreachable]

Question¶

What will be the output?

public static int sum(int a, int b){
  return a+b;
}
public static void main(){
  int a = 10, b = 5;
  int x = 100, y = 200;
  System.out.pritnln(sum(x,y));
}

Choices¶

300
15
Compilation Error

Explanation

We get answer 300 because value passed to function sum was 100 and 200 respectively(i.e. values of x and y of main function ) hence value of variables a and b in function sum is set to 100 and 200 respectively and value of variables a and b in function sum is independent of the values of a and b defined in function main.
Therefore we can say that variables in a function are defined only in scope of the function.

Question¶

What will be the output?

public static int sum(int a, int b){
  int x = 20, y = 30;
  return a+b;
}
public static void main(){
  int a = 10, b = 5;
  int x = 100, y = 200;
  System.out.pritnln(sum(x,y));
}

Choices¶

300
15
Compilation error

Explanation

We get answer 300 because value passed to function sum was 100 and 200 respectively(i.e. values of x and y of main function ) hence value of variables a and b in function sum is set to 100 and 200 respectively and value of variables a and b in function sum is independent of the values of a and b defined in function main.
Also x and y defined in sum() & x and y defined in main() are separate entities and changing the value of x and y in sum() won't affect the x and y defined in main().

Question¶

What will be the output?

public static int sum(int a, int b){
    a = 20; b = 30;
    return a+b;
}
public static void main(){
    int a = 10, b = 5;
    int x = 100, y = 200;
    System.out.pritnln(sum(x,y));
}

Choices¶

50
300
Compilation error

Explanation

We get answer 50 because value passed to function sum was 100 and 200 respectively(i.e. values of x and y of main function ) hence value of variables a and b in function sum is set to 100 and 200 respectively and value of variables a and b in function sum is independent of the values of a and b defined in function main.
But in sum() we set the value of a and b to 20 and 30 respectively since a and b are defined within scope of sum() there values are changed.

Question¶

What will be the output?

public static int sum(int a, int b){
  int a = 20, b = 30;
  return a+b;
}
public static void main(){
  int a = 10, b = 5;
  int x = 100, y = 200;
  System.out.pritnln(sum(x,y));
}

Choices¶

50
300
Error

Explanation

We get compilation error because we declared variables that are already defined in function sum()