Java For Loop Logic

Question

Okay, i'm a beginner learning from "Java Beginner Guide" Book from Herbert Schildt. Here is piece of code i run across when learning for loop chapter.

the code basicly ask for user input and if the user input match with condition which is "s" the loop wont start, if its match its star and print "pass# + i" each time its iterates.

my question is why when i input anything except "s" the output is two line of "pass#"? why not just one line?

    System.out.println("pls type s");

    for( i = 0; (char) System.in.read() != 's'; i++)
        System.out.println("pass#" + i);

Wow, I've never thought of doing a for loop like that where the condition is completely unrelated to the iterator. Honestly kind of confusing at first (for me at least) — MCMastery, Oct 27 '19 at 03:31
You hit `enter` button when you finish input, System will reads it. — Tangoo, Oct 27 '19 at 03:37

score 1 · Answer 1 · edited Oct 27 '19 at 04:11

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It's due to pressing enter after an input, which signals the shell to put your input, which includes the enter press, into standard input. Enter itself has an ASCII value. So, it (enter) is also counted as a character.

Try pressing enter only; you will see a pass# message.

edited Oct 27 '19 at 04:11

Bohemian

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answered Oct 27 '19 at 03:46

Shakib Uz-Zaman

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But once the `s` is read, the loop exits – Bohemian Oct 27 '19 at 04:13

score 0 · Answer 2 · answered Oct 27 '19 at 05:04

The System.in.read() function reads data byte wise. So,when you type a character and press enter....what happens is,

Prompt:pls type s

Input:a(press enter)

Java perceives this as: "a \n" as enter is also accounted as a byte value.

As a result of two bytes the print statement is run two times.

Java For Loop Logic

2 Answers2