Getting a run time error on this divisible sub array code is given

#1

#include<bits/stdc++.h>
using namespace std;
int main() {
int t;
cin>>t;
while(t–)
{
long long n,ans=0;
cin>>n;
vectorv(n),pre(n+1,0),c(n,0);
for(int i=0;i<n;i++)
{
cin>>v[i];
}
for(int i=0;i<n;i++)
{
pre[i+1]=pre[i]+v[i];

	}
	for(int i=0;i<=n;i++)
	{
		pre[i]%=n;
	}
	for(int i=0;i<=n;i++)
	{
		c[pre[i]]++;
	}
	for(int i=0;i<n;i++)
	{
		ans+=((c[i]*(c[i]-1))/2);
	}
	cout<<ans<<endl;
}
return 0;

}

#2

Now it’s working https://ide.codingblocks.com/s/572204. You weren’t performing modular arithmetic correctly.

#3

explain why we do p[i+1]=(p[i+1]+n)%n after p[i+1]%=n; it would de great if great

#4

Reason being p[i] can be negative as array can have negative elements.
You can study about it from here https://www.hackerearth.com/practice/math/number-theory/basic-number-theory-1/tutorial/

#5

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