The following code is meant to find total numbers between l and r whose product of digits is even (for multiple test cases t). This code runs perfectly but is extremely slow for r greater than 100000. Can anyone suggest a better alternative?

#include 
#include 
using namespace std;
long long int nd(long long int x, int n) //return the digit at a particular index    staring with zero as index for unit place
{
while (n--) {
    x /= 10;
}
return (x % 10);
}
int ng(long long int number) //returns total number of digits in an integer
{
int digits = 0;
if (number < 0) digits = 1;
while (number) {
    number /= 10;
    digits++;
}
return digits;
}

int main()
{
int t;
cin>>t;
long long int l[t], r[t], c;
for(long long int j=0;j>l[j]>>r[j];
}
for(long long int k=0;k