Doubt in prime sieve video

#1

what is LL used in this video,and in this video prateek bhaia 1st mark all odd no. as prime no. and loop is stated from i=3 and is inrmented as i++,and it will surely go to 4,6,8,10,…
so how it can go and mark all odd no. as prime.

#2

LL denotes long long
he must have defined the declaration as

#define ll long long
in the vedio he is incrementing i twice
for (ll int i=3;i<1000000;i+=2)
so it won;t go for even numbers we have done this for optimization as we are know that even numbers can’t be prime(except 2)

even if we had incremented i once then also we have initialized p with 0 so even numbers are already stated as non prime and for 2 we are making 2 explicilty prime by doing p[2]=1;

#3

sir ,till now prateek bhaiya did not tell about any #define ll long long…,what is this plese tell me.

#4

The #define preprocessor allows us to define symbolic names and constants. For example,

#define PI 3.14159
This statement will translate every occurrence of PI in the program to 3.14159.

#define allows you to make text substitutions before compiling the program. Here’s an example :
#define NAME “Computer Science C++”

Every time the preprocessor sees NAME it will replace it with “Computer Science C++”

if you don;t know about preprocessor then i highly suggest you to read this article
https://www.learncpp.com/cpp-tutorial/introduction-to-the-preprocessor/

#5

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