I have doubt in code of Divisible subarrays problem

#1
  1. If I declare ll a[1000005],pre[1000005]; in main, I am getting segmentation error. Why??
  2. Why are we doing sum=(sum+n)%n; for negative numbers and getting the correct answer?
#2

hello @sahilkhan2312000131

when u declare array in function then it get allocated in stack , whereas when we make array global then it is stored in data segment.data segment allow more memory compared to stack that why we see such behaviour.

its a mod property .
when we do sum% n then it gives us number in range [-(n-1)…(n-1)]

so to make it non negative we add n ,and then take its mod.

i would recommend to read about all mod property.

#3

When we make Prime sieve we declare array of the same size inside main and get no error but here we are getting error why?

#4

share that code with me

#5

#include<bits/stdc++.h>
using namespace std;
void abc(int p[]){
for(int i=3;i<=1000000;i+=2){
p[i]=1;
}
for(long long i=3;i<=1000000;i+=2){
if(p[i]==1){
for(long long j=i*i;j<=1000000;j+=i){
p[j]=0;
}
}
}
p[2]=1;
p[1]=p[0]=0;
}
int main() {
int p[1000005]={0};
abc§;
int sum[1000005]={0};
for(int i=1;i<=1000000;i++){
sum[i]=sum[i-1]+p[i];
}
int t; cin>>t;
while(t–){
int a,b;
cin>>a>>b;
cout<<sum[b]-sum[a-1]<<endl;
}
return 0;
}
This is code for Prime visits problem

#6

Replace int with long long and then run

#7

Ok, I got it…Thank you so much

#8

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