Hello guyz please help me with this problem.there's already a predefined array/list containing 100 integer values. Loop through each values, compute their squares, and display them.

Quote:

Hello guyz please help me with this problem.there's already a predefined array/list containing 100 integer values. Loop through each values, compute their squares, and display them.

This is not what your code is doing. your code do not output anything because it don't try to.
To understand what your code is doing, use the debugger, it will show you;

Advice: Learn to indent properly your code, it show its structure and it helps reading and understanding. It also helps spotting structures mistakes.

import java.util.Scanner;

class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		List<integer> Numbers = new ArrayList<integer>();
		int num[] = new int[100];
		for (int i = 1; i <= num.length; i ++) {
			Numbers.add(i * i);
		}

		if(Numbers.contains(10000)) {
			int a = 1;

			int user = sc.nextInt();
			while(a < 100) {
				if(Numbers.contains(user)) {
					user = sc.nextInt();
					a++;
				}else {
					break;
				}
			}
		}
	}
}

Indentation style - Wikipedia[^]
Best C++ Formatter and Beautifier[^]
Online C/C++ Formatter, Indenter and Beautifier – Techie Delight[^]

Professional programmer's editors have this feature and others ones such as parenthesis matching and syntax highlighting.
Notepad++ Home[^]
ultraedit[^]
Enabling Open Innovation & Collaboration | The Eclipse Foundation[^]

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

jdb - The Java Debugger[^]
https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.
[Update]

Quote:

dont know where's the 10000 came from,

May be it comes from 100*100