CODEWITHSUNDEEP
javafor-loopinfinite-loop
kakarotto
kakarotto

Reputation: 21

What is the reason for these two for loop acting differently?

Hi can anyone help me with this?

First block of codes gives the output as intended. But second one goes for infinite loop. What is the reason?

Thank you.

1.

import java.util.Scanner;
class Numbers
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter a starting number: ")
        int start = scan.nextInt();

        for(int a = start;a<=(start+10);a++)
        {
             System.out.println(a);
        }

    }
}

2.

import java.util.Scanner;
class Numbers
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter a starting number: ")
        
        for(int start = scan.nextInt();start<=(start+10);start++)
        {
             System.out.println(start);
        }

    }
}

Upvotes: 1

Views: 87

Answers (3)

dani-vta
dani-vta

Reputation: 7130

In your second snippet, you have a semantic error, since you're comparing start to itself plus 10.

for(int start = scan.nextInt(); start <= (start + 10); start++)

Regardless of what you perform in a loop, a variable is always equal or lower than itself plus 10, hence the conceptually infinite loop. In reality, just a really long loop until start + 10 overflows to Integer.MIN_VALUE, turning the condition to false.

To fix your code, you should use a different variable to keep track of the loop iteration (as you did in the first snippet), leaving start unmodified and just for confrontation to terminate the loop.

Upvotes: 1

DrakeLiam
DrakeLiam

Reputation: 123

In the first block, start is a constant variable which has fixed value and the condition is between a and start (a keeps increasing a++ and start won't change its value).

While in second block, the condition is between start and start+10, but start keeps increasing with start++ in the loop function, which makes the loop is infinite (start keeps changing its value so start<=(start+10) is always true).

Upvotes: 2

Yunnosch
Yunnosch

Reputation: 26763

This for(int start = scan.nextInt();start<=(start+10);start++) compares the changing variable to a changing value, which keeps the same distance ahead.
I.e. the value of start will always be lower than start+10, what you get is at first an endless loop. It can only terminate when values get so high that they cannot be represented anymore an strange things occur. At that point start+10 might appear to be lower than 0 for example and hence seem also lower than start which not yet is past that weird border.

Upvotes: 2

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