A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99. Find the largest palindrome made from the product of two n-digit numbers.

largest_palendrome_product.c

#include<math.h>
#include<stdlib.h>
int is_palindrome(int n){
	int len=0;
	while(n/(int)pow(10,len)) len++;
	while(len>1){
		int mul=pow(10,len-1);
		int d1=n/mul;
		int d2=n%10;
		if(d1!=d2) return 0;
		n-=d1*mul;
		n/=10;
		len-=2;
	}
	return 1;
}
int largest_palendrome_product(int digit){
	int max=(int)pow(10,digit)-1;
	int min=(int)pow(10,digit-1);
	int ret=-1;
	for(int i=max;i>=min;i--){
		for(int j=max;j>=min;j--){
			int num=i*j;
			if(num>ret && is_palindrome(num)) ret=num;
		}
	}
	return ret; 
}