Friday, 29 May 2015

Java Iteration Statements (Loop Control Structure)

The Java supports the while, do-while and for iteration/loop control statements. The syntax is similar to C/C++. With JDK1.5, a second form of for was added that implements a “for-each” style loop.

while Statement

The general form of a while statement is:

while(condition)

loop body

Loop body may contain one or more statements. If loop body contains more than one statement then they must be enclosed between braces.

Example: The following program accepts one natural number say n as command line argument and then calculates and displays the sum of first n natural numbers.

class SumNaturalNumbers

{

public static void main(String a[])

{ int n, sum=0;

n = Integer.parseInt(a[0]); //command line argument

int i = 1;

sum = 0;

while (i <= n)

{

sum = sum + i;

i  = i + 1;

}

System.out.println("Sum of first " + n + " natural numbers is " + sum);

}

}

do-while Statement

The general form of a do-while statement is:

do

{

} while (condition)

loop body

Example: The following program accepts one integer number say n as command line argument and then calculates and displays the sum of its digits.

class SumOfDigits

{ public static void main(String a[])

{ int n, m, sum, digit;

n = Integer.parseInt(a[0]); //command line argument

m = n;

if(m < 0)

m = -m;

sum = 0;

do

{ digit = m % 10;

sum = sum + digit;

m = m / 10;

}while (m > 0);

System.out.println("Sum of digits of number " + n + " is: " + sum);

}

}

for Statement

The general form of a for statement is:

for(initialization; condition; increment/decrement)

loop body

Loop body may contain one or more statements. If loop body contains more than one statement then they must be enclosed between braces.

Example: The following program accepts one natural number say n as command line argument

and then calculates and displays the sum of first n natural numbers.

class SumNaturalNumbers1

{ public static void main(String a[])

{ int i, n, sum;

n = Integer.parseInt(a[0]); //command line argument

for(i = 1, sum = 0; i <= n; i++)

{

sum = sum + i;

}

System.out.println("Sum of first " + n + " natural numbers is " + sum);
}
}


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