The for-statement

Different loop-statements in Java

Java provides 3 types of loop-statements:

1. The for-statement

2. The while-statement

3. The do-while-statement

The for-statement (1)

The for-statement is ideally suited for making the following type of program:

Let some variable x take on a series of value one at a time

For each value taken on by a variable x, the body of the for-statement is executed once.

repeat ( for x = 1, 2, 3, .... 10 )

execute this statement;

The for-statement (2)

Flow chart of a for-statement

The most common way to use a for-statement (2)

The most common way to use a for-statement (3)

public class For01{

public static void main(String[] args) { int a;

for ( a = 1 ; a <= 10 ; a = a + 1 ) { System.out.println(a); // Print a }

System.out.println("Done"); }}

The most common way to use a for-statement (1)

The for-statement was originally invented to let some variable take on a series of value

for ( var = START_VALUE ; var <= STOP_VALUE ; var = var + INCR )

{

/* for-body (statements) */

}

For each of the value, the statements in the for-body are executed

Flow chart of this program:

Programming example 1: find all divisors of a number (1)

Write a Java program that reads in an integer n... and prints all its divisors

Input: n = 12

Output: 1, 2, 3, 4, 6, 12

Programming example 1: find all divisors of a number (2)

Check if 12 is divisible by 1

Check if 12 is divisible by 2

...

Check if 12 is divisible by 12

We do not need to check numbers > 12 because only number ≤ 12 can be divisors !

Programming example 1: find all divisors of a number (3)

for (x = 1, 2, 3, ...., 10) do

{

print x;

}

This notation can be converted to a for-statement very naturally:

for ( x = 1; x <= 10; x = x + 1 )

{

print x;

}

Programming example 1: find all divisors of a number (4)

public class Divisors01{ public static void main(String[] args) {

Scanner in = new Scanner(System.in); int n, x;

n = in.nextInt(); // Read in number

for ( x = 1; x <= n; x++ ) // Run x = 1, 2, ..., n{

if ( n % x == 0 ) { // x is a divisor of n

System.out.println(x); }

}}

}

Programming example 2: compute the sum 1+2+3+...+n (1)

input: n = some integer number

sum = 0; // Clear the running total !

for ( x = 1, 2, 3, ..., n ) do

{

Add x to sum

}

Print sum;

Programming example 2: compute the sum 1+2+3+...+n (2)

public class Divisors01{

public static void main(String[] args){

Scanner in = new Scanner(System.in); int n, x, sum = 0; System.out.print("Enter a number n: "); n = in.nextInt(); // Read in number

for ( x = 1; x <= n; x++ ) // Run x = 1, 2, ..., n {

sum = sum + x; // Add x to sum}System.out.println(sum); // Print final sum

}}

Programming example 3: compute factorial n! (1)

Write a Java program that reads in an integer n... and prints the factorial n! = 1×2×3×...×n

Input: n = 5

Output: 120 (because 1 × 2 × 3 × 4 × 5 = 120)

Programming example 3: compute factorial n! (2)

input: n = some integer number

product = 1; // Set running product to 1

for ( x = 1, 2, 3, ..., n ) do

{

Multiply x into product

}

Print sum;

Programming example 3: compute factorial n! (3)

public class Factorial01 {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int n, x, product = 1;

System.out.print("Enter a number n: ");

n = in.nextInt(); // Read in number

for ( x = 1; x <= n; x++ ) {

product = product * x; // Multiply x into product

}

System.out.println(product); // Print final product

}

}

The break and continue statements

• Introduction

• There are 2 special statements that can affect the execution of loop statements (such as a for-statement)

• The special statements are:

■ break

■ continue

• We will study their meaning and how to use these special statements inside the while-statement

Effect of the break and continue statements on the for-statement (1)

The continue statement

• Syntax:

continue;

Effect:

◦ When the continue statement is executed inside a loop-statement, the program will skip over the remainder of the loop-body to the end of the loop body

◦ Note:

■ What happens next when the program reaches the end of a loop depends on the type of loop statement !!!

Effect of the break and continue statements on the for-statement (2)