Largest palindrome built with n digits

004.palindromeLargest.cpp

// 004.palindromeLargest.cpp
// juanfc 2012-06-24
// A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 x 99.
// Find the largest palindrome made from the product of two 3-digit numbers.

#include <iostream>
using namespace std;

const int NOOFDIGITS = 3;

bool isPalind(int);

int main()
{

    // find the limits
    int baseTop = 1;
    for (int i = 0; i < NOOFDIGITS; ++i) {
        baseTop *= 10;
    }
    int baseBot = baseTop / 10;

    int greatestPal = 0;
    int ii, jj;
    int test;
    for (int i = baseTop-1; i >= baseBot; i--) {
        for (int j = baseTop-1; j >= i; j--) {
            test = i * j;
            if (isPalind(test) and test > greatestPal) {
                greatestPal = test;
                ii = i;
                jj = j;
            }
        }
    }

    if ( greatestPal == 0 )
        cout << "None" << endl;
    else
        cout << greatestPal << ": " << ii << "x" << jj << endl;
    return 0;
}

bool isPalind(int a)
{
    // here you need to convert the int to its decimal string chars
    // it can be done several ways:
    char s[24];
    sprintf(s, "%d", a);

    int i = 0;
    int j = 0;

    // length
    while (s[j] != '\0')
        j++;

    --j; // last char

    while (i < j and s[i] == s[j]) {
        ++i;
        --j;
    }

    return i >= j;
}
// 1: 9: 3x3
// 2: 9009: 91x99
// 3: 906609: 913x993
// 4: 99000099: 9901x9999