help !!!! to understand this code!

Question

Given an integer X within the range of 0 to 9, and given two positive integers as upper and lower bounds respectively, find the number of times X occurs as a digit in an integer within the range, excluding the bounds. Print the frequency of occurrence as output.
using namespace std;

int main() {
int t;
cin>>t;
while(t--)
{int l,u,x;
cin>>x;
cin>>l>>u;
int c=0;
for(int i=l+1;i<u;i++)
{int num=i;
while(num!=0)
{
if(num%10==x)
{c++;}
num=num/10;}}
cout<<c<<endl;
}
return 0;
}