Another doubt in Bucket sort in c++

#1

Please explain me the following lines of code that bhaiya has explained inside the bucketsort function:
for(int i=100;i>=0:i–)
{
for(vector:: iterator it=v[i].begin(); it! =v[i].end();it++)
{
------@

}
}
Please explain both the above loops

#2

see we need a sorted array at the end
on the basis of marks
hence we are iterating from the maximum marks
for(int i = 100 ; i >=0 ; i–)

and since we need to tell the student name and marks at the corresponding index
hence we iterate over the vector using
for(vector:: iterator it=v[i].begin(); it! =v[i].end();it++)

u will study about how to iterate over the vector in the future videos