Daught regarding prime sieve code

#1

code-https://ide.codingblocks.com/s/198699
trying to print prime no from 1 to 100 using sieve but getting output as 0 .cant figure out mistake

#2

not getting output after making correct at line no-17 as a[1]=a[0]=0

#3

you are not taking input p; write statement cin>>p.

Hope it Helps.