Control/Lopping Statement : For loop and While loop

What is for and while loop?

• loops are used to repeat a block of code. For example, if we want to show a message 100 times,then rather than typing the same code 100 times, we can use a loop.
• loop is used to run a specific code until a certain condition is met.

while loop:

• A while loop evaluates the expression inside the parenthesis ().
• If the expression evaluates to true, the code inside the while loop is executed.
• The expression is evaluated again.
• This process continues until the expression is false.
• When the expression evaluates to false, the loop stops.

Example :

class LearWhileLoop{
  public static void main(String[] args) {

    int i = 1;
    while(i <= 5) {
      System.out.println(i);
      i++;
    }
  }
}

output :
1
2
3
4
5

for loop:

• The initialexpression initializes and/or declares variables and executes only once.
• The condition is evaluated. If the condition is true, the body of the for loop is executed.
• The updateexpression updates the value of initialexpression.
• The condition is evaluated again. The process continues until the condition is false.

Example :

class LearForLoop{
  public static void main(String[] args) {

    int n = 5; 
    for (int i = 1; i <= 5; ++i) {
      System.out.println(i);
    }
  }
}

Output:
1
2
3
4
5

• We use for loop when we know how many times the loop should run.
• We use while when the loop depends on a condition, not a fixed number.

Example :

    public static void main(String args[]) {
    {

        Scanner sc = new Scanner(System.in);
        boolean bl = true;
        while(bl)
        {
            System.out.print("Enter a character in small alphabet: ");
            char ch = sc.next().charAt(0);
            if(ch >='a' && ch <= 'z') {
                System.out.println("Good! you have entered a vowel");
                bl = false;
            }
            else
                System.out.println("Entered Character is not vowel");
        }

    }

But we can also do this in for loop

    public static void main(String args[])
        {

            Scanner sc = new Scanner(System.in);
            boolean bl = true;
            for (; bl; ) {
                System.out.print("Enter a character in small alphabet: ");
                char ch = sc.next().charAt(0);
                if (ch >= 'a' && ch <= 'z') {
                    System.out.println("Good! you have entered a vowel");
                    bl = false;
                } else
                    System.out.println("Entered Character is not vowel");
            }

        }