Could you please tell me the Palindrome number checking code?

Answer 1

The most efficient method is to reverse the digits in the number and then check if the reversed number is equal to the original number. In C, we can implement this as follows (using long-hand notation for clarity). Note the use of base (defaulting to base 10) so that we can check values in other bases.

bool is_palindrome (unsigned num, unsigned base = 10) {

// local variables

unsigned rev, digit, digits;

// copy the input number

digits = num;

// initialise the accumulator

rev = 0;

// repeat while there are digits

while (digits) {

// extract the low-order digit using modulo (%) operator

digit = digit % base;

// shift the accumulated digits (if any) one position to the left

rev = rev * base;

// add on the new digit

rev = rev + digit;

// shift the remaining digits one position to the right

digits = digits / base;

} // end while

// return true if the number and its reverse are equal

return num == rev;

}

Answer 2

To determine if a number is a palindrome, we need to reverse the number to see if it is the same as the original number. If the number were 12345, the reverse would be 54321. They are not equal, so the number is not a palindrome. But if the number were 12321, the reverse would also be 12321, so the number is a palindrome.

To achieve this in code we need two functions, one to reverse the number and the other to determine if the number is a palindrome. We use two functions instead of one because reversing a number is a useful function in and of itself. It also makes code easier to read when every function does just one simple job.

unsigned reverse (unsigned number)

{

unsigned accumulator=0; // initialise an accumulator

while (number) // repeat while the number is non-zero

{

accumulator *= 10; // move all accumulated digits one place to the left

accumulator += number%10; // add the least significant digit of the number (modulo 10)

number /= 10; // move all digits one place to the right

}

return accumulator; // the accumulator is the reverse of the original number

}

bool is_palindrome (unsigned number)

{

return number reverse (number, base);

}