prime1 ques 2

[namanjain2050]

PLEASE HELP ME HERE
I AM STUCK AT THIS QUESTION FROM PAST 3 DAYS
I AM GETTING A SIGFPE RUNTIME ERROR FOR THIS CODE

#include<bits/stdc++.h>
#define MAX_NO 1000000000
using namespace std;
void SimpleSieve(vector<int> &prime)
{
    int limit = (int) ceil(sqrt(MAX_NO));
    bool mark[limit+1];
    memset(mark,true,sizeof(mark));
    for(int p=2;p*p<=limit;p++)
    {
        if(mark[p])
        {
            for(int i=2*p;i<=limit;i+=p)
                mark[i]=false;
        }
    }
    for(int p=2;p<=limit;p++)
    {
        if(mark[p])
            prime.push_back(p);
    }
}
int main()
{
    vector<int> prime;
    SimpleSieve(prime);
    int t,low,high,temp,flag;
    cin>>t;
    while(t--)
    {
        cin>>low>>high;
        for(int i=low;i<=high;i++)
        {
            flag=0;
            if(i==1)
                continue;
            else if(i==2 || i==3)
                cout<<i<<endl;
            else
            {
                temp=(int) floor(sqrt(i));
                for(int j=0;;j++)
                {
                    if(prime[j]<=temp)
                    {
                        if((i%prime[j])==0)
                        {
                            flag=0;
                            break;
                        }
                        else
                        {
                            flag=1;
                            continue;
                        }
                    }
                    else
                        break;
                }
            }
            if(flag==1)
                cout<<i<<endl;
        }
        cout<<endl;
    }
}

[leppyr64]

SIGFPE is usually caused by division by zero. You are dividing by zero.

When posting code, please paste it in, select it, and click the preformatted text button.

[namanjain2050]

But where i am dividing by zero?

i cross checked many times

[leppyr64]

You only divide in one place, so it must be right there (and it is)

[namanjain2050]

I am taking (i%prime[j]) where prime is an array in which I stored all the prime numbers upto ~32000
and it does not contain a zero, so why am I getting this error

[leppyr64]

Well, it's true that you're not directly inserting a zero into prime, that doesn't mean that there's not one.

What is the largest number in prime[]? Take it's square. Think about how you use those numbers in other portions of your code nearby.

[namanjain2050]

why will i take the square of my largest prime?

[leppyr64]

What is the value?

[namanjain2050]

largest prime is 31607

[leppyr64]

31607^2 = 999002449

What's the largest prime in the input set?

[namanjain2050]

the constrains are 1<=m<=n<=10^9

[leppyr64]

That was not the answer to my question. If you want help then you need to think.

[namanjain2050]

ohh i am sorry

But i didný get your question.
input set as in what user entered the two limits ?

[leppyr64]

The largest number in the input set will be 10^9 but what will be the largest possible prime that occurs in your output?

[namanjain2050]

i believe it will be 999999937

[leppyr64]

i believe it will be 999999937

And what is the square root of this number?

[namanjain2050]

it will be approximately 31622

[leppyr64]

So the largest number in your list of primes is 31607 but you want to stop looping when that value reaches the square root of the number being input (temp) which can be as large 31622. What happens next?

[namanjain2050]

ok i get you, but what's the alternative here?
why algorithm is like I take the square root of input(i) and store it in temp
Than check for every prime in prime array that is less than temp if i is divisible by any of those primes its considered not prime.
And still is this is the problem by am i getting a RE shouldn't i be getting a WA error?

[namanjain2050]

its my instead of why in second line