13,868,977 members
See more:
```public class prob_4
{

public static void main(String[] args)
{
int product = 0;
int rev = 0;
int max_product = 0;
int r;

for(int i=100;i<=999;i++)
{
for(int j=101;j<=999;j++)
{

product = i * j;

if(product < max_product)
{
break;
}
int number = product;

while(number > 0)
{
r =  number % 10;
rev = (rev * 10) + r;
number = number/10;
}

if(product == rev && product > max_product)
{
max_product = product;
}

}

}

System.out.println(max_product);
}

}
```

What I have tried:

`I am tring my best for solving this question but i got 0 answer after run the code....whats wrong in that code?`
Posted
Updated 8-Dec-18 1:59am
Graeme_Grant 8-Dec-18 6:40am

This is homework, a chance for you to show that you understand. Work out the answer on paper like a normal math question then convert it to code.

To help you a little with your program, the question is "Find the largest". So would it not be quicker to work from the largest to smallest number rather than from the smallest to the largest?

I found same result in largest to smallest also...

## Solution 1

Hint: 101*101=10201, 111*111=12321
First use it to test if your code is correct to detect palindromes.
Quote:
I checked my "rev" value its geting weird......what is wrong in reverse logic ?

What is the starting value of `rev` when you reverse a number ?
Use the debugger to watch what you do with it.

For testing purpose, change the range of values to 100-112 and use the debugger to see what your code is really doing.
-----
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.

The downside of this solution:
- It is a DIY, you are the one tracking the problem and finding its roots, which lead to the solution.
The upside of this solution:
- It is also a great learning tool because it show you reality and you can see which expectation match reality.

secondary effects
- Your will be proud of finding bugs yourself.
- Your learning skills will improve.

You should find pretty quickly what is wrong.

Debugger - Wikipedia, the free encyclopedia[^]

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

http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html[^]
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.
v2

public class Prob_4
{

public static void main(String[] args)
{
int product = 0;
int rev = 0;
int max_product = 0;
int r;

for(int i=100;i<=999;i++)
{
int j = i;

product = i * j;
System.out.println(product + " " + i + " " + j);

if(product < max_product)
{
break;
}

int number = product;

while(number > 0)
{
r = number % 10;
rev = (rev * 10) + r;
number = number/10;
}

if(product == rev && product > max_product)
{
max_product = product;
}

}

System.out.println(max_product);
}

}

Give same ouput as 0.
Patrice T 8-Dec-18 8:18am

Use Improve question to update your question.
So that everyone can pay attention to this information.
and explain problems with the code.

public class Prob_4
{

public static void main(String[] args)
{
int product = 0;
int rev = 0;
int max_product = 0;
int r;

for(int i=100;i<=999;i++)
{
//int j = i;
for(int j=100;j<=999;j++)
{

product = i * j;
System.out.println(product + " " + i + " " + j);

if(product < max_product)
{
break;
}

int number = product;

while(number != 0)
{
r = number % 10;
rev = (rev * 10) + r;
number = number/10;

}

System.out.println(rev);

if(product == rev && product > max_product)
{
max_product = product;
}

}
}

System.out.println(max_product);
}

}

I checked my "rev" value its geting weird......what is wrong in reverse logic ?

Top Experts
Last 24hrsThis month
 CPallini 90 OriginalGriff 90 Afzaal Ahmad Zeeshan 60 RickZeeland 40 Richard MacCutchan 30
 OriginalGriff 5,808 Maciej Los 2,460 Richard MacCutchan 2,350 Dave Kreskowiak 1,733 CHill60 1,325