What does array[++variable] stand for?

Question

Sample code here:

static class stack 
{
    int top=-1;
    char items[] = new char[100];

    void push(char x) 
    {
        if (top == 99)
            System.out.println("Stack full");
        else
            items[++top] = x;
    }
}

What exactly happens when items[++top] occurs?

What part of the code is not clear? Is it the `items[...]` syntax or the `++top` syntax? Or both? — Daniel Pryden, Jan 16 '18 at 13:44
Look up `pre-increment` and `post-increment` to explain the `++top`. [Here is a link to Java docs for arrays](https://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html) — TheCrzyMan, Jan 16 '18 at 13:47
[What does x-- or x++ do here?](https://stackoverflow.com/q/4104944) [What is the difference between a += b and a =+ b , also a++ and ++a?](https://stackoverflow.com/q/5098282) [Assignment, Arithmetic, and Unary Operators](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/op1.html) — Bernhard Barker, Jan 16 '18 at 14:00

Vel · Accepted Answer · 2018-01-16T13:46:36.740

6

It's pre incrementation. It's equal to:

void push(char x) 
    {
        if (top == 99)
            System.out.println("Stack full");
        else {
            top = top + 1;
            items[top] = x;
        }

    }

edited Jan 16 '18 at 13:46

answered Jan 16 '18 at 13:42

Vel

524
3
11

It is pre increment – Amit Jan 16 '18 at 13:43
1

oh yeah I've realised that just after posting, my bad. – Vel Jan 16 '18 at 13:43
2

The curly brace for the else block is missing – Jan 16 '18 at 13:46
You're right, I've added it. – Vel Jan 16 '18 at 13:47

Youcef LAIDANI · Answer 2 · 2018-01-16T13:50:57.173

2

This called Pre-increment, so this items[++top] = x; equivalent to :

top++; // this also equivalent to top+=1; or top = top + 1;
items[top] = x;

edited Jan 16 '18 at 13:50

answered Jan 16 '18 at 13:43

Youcef LAIDANI

55,661
15
90
140

What does array[++variable] stand for?

2 Answers2