user1440323 user1440323 - 4 years ago 113
C# Question

Finding out whether a number is a palindrome or not in C#

I am new to C# and was doing this program as an exercise. I have managed to get my program to print the reversed number of the input given by the user, but when I move onto checking whether it is a palindrome or not, it does not calculate the answer correctly. It always prints 'not a palindrome'.

After some error checking, I realized that the reason why it was doing this is because the last number that gets stored in

is just the last digit after being reversed and not the entire number. How can I rectify this??

My Code

int i, remainder = 0, newnum = 0;
Console.WriteLine("Enter a Number: ");
int uinput = Convert.ToInt32((Console.ReadLine()));
for (i = uinput; i > 0; i = (i / 10))
remainder = i % 10;

newnum = remainder;


if (newnum == uinput)
Console.WriteLine("The Number {0} is a palindrome", uinput);
Console.WriteLine("Number is not a palidrome");

I also looked online at another code example, but the thing I don't understand in that is why num is being converted to boolean type in the while loop? Is that just to keep the loop running?

The Code reffered to above

int num, rem, sum = 0, temp;
Console.WriteLine("\n >>>> To Find a Number is Palindrome or not <<<< ");
Console.Write("\n Enter a number: ");
num = Convert.ToInt32(Console.ReadLine());
temp = num;
while (Convert.ToBoolean(num))
rem = num % 10; //for getting remainder by dividing with 10
num = num / 10; //for getting quotient by dividing with 10
sum = sum * 10 + rem; /*multiplying the sum with 10 and adding
Console.WriteLine("\n The Reversed Number is: {0} \n", sum);
if (temp == sum) //checking whether the reversed number is equal to entered number
Console.WriteLine("\n Number is Palindrome \n\n");
Console.WriteLine("\n Number is not a palindrome \n\n");

Any sort of help is much appreciated!! Thank You :)

Answer Source

I'm not sure what you're asking, since the second snippet of code you found online should fix your issue. Your code works, if you just change the line

newnum = remainder;


newnum = (newnum*10) + remainder;

The issue in your case is not the condition you used in the for loop, it's just that you're overwriting newnum with the remainder every time, so newnum is only storing the last reminder that was calculated in the loop, "forgetting" all the others it had calculated before.

To reverse the number, every time you enter the loop, you should add the last remainder you've found to the right of newnum, which is effectively equivalent to multiplying everything by 10 and adding remainder.

Try to follow it step by step with pen and paper (or with a debugger).

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