Sieve of erastosthene

#1

for( ll j=i*i; i<=n;J=j+i)

in the above code what does ll j mean cuz in the video explanation this concept was used

#2

ll used here means long long int
You can define it earlier as -
#define ll long long
and then use ll wherever you want long long int.

#3

ll used stands for long long int.
It’s a macro
and can be declared like
#define ll long long