Prime no between m and n - c

Question

I tried a prime no generating question in SPOJ(link : http://www.spoj.com/problems/PRIME1/) .
I'm using seive algorithm . I get the SIGSEGV error when i use spoj gcc . But when i compiled using my ubuntu gcc it works for all the test cases.
Here is my source code . Plz Help
float sqroot( float x)
{
float a , b;
a = x; // copy given value to 'a'
do
{
b = a; // copy value of 'a' to 'b' before 'a' is modify
a = (a + x/a) / 2; // modify 'a' value until we reach sqroot result
}
while( a!= b); // execute loop until a == b
return( a); // 'a ' or 'b' is sqroot of 'x'
}
int main()
{
int prime[4000];
int prime_index=0;
bool find_prime[100001];
int i,j;
int m,n;
int iremainder;
int T,t_index;
int PRIME_FLAG=1;
float square;
int limit;
prime_index++;
prime[prime_index]=2;
for(i=3;i<=32000;i=i+2)
{
PRIME_FLAG=1;
square = sqroot((float)i);
limit = ((int)(square))+1;
for(j=1;j<=prime_index,prime[j]<=limit;j++)
{
if(prime[j]!=0)
{
if((i%prime[j]) == 0)
{
PRIME_FLAG = 0;
break;
}
}
}
if(PRIME_FLAG)
{
prime_index++;
prime[prime_index]=i;
printf("%d\n",i);
}
}
printf("Enter the no of test cases:");
scanf("%d",&T);
if(T<=10)
{
for(t_index=1;t_index<=T;t_index++)
{
printf("Enter the values of m and n :");
scanf("%d%d",&m,&n);
if((m>=1) && (n<=1000000000) && ((n-m)<=100000))
{
if(m == 1)
m=2;
//Set all numbers from m to n as prime
for(i=m;i<=n;i++)
find_prime[i]=true;
//Find the prime numbers between m to n
square = sqroot((float)n);
limit = ((int)(square))+1;
for(i=1;i<=prime_index,prime[i]<=limit;i++)
{
if(m>=prime[i])
{
if(prime[i]!=0)
iremainder=m%prime[i];
j=prime[i]*iremainder;
}
else
{
iremainder=prime[i]-m;
if(m+iremainder == prime[i])
j=2*(m+iremainder);
else
j=m+iremainder;
}
for(;j<=n;j=j+prime[i])
find_prime[j]=false;
}
//Print all prime no's
for(i=m;i<=n;i++)
{
if(find_prime[i])
printf("%d\n",i);
}
}
}
}
return 0;
}

Answer 1

your for loops are wrong.
for(j=1;j<=prime_index,prime[j]<=limit;j++)
should be
for(j=1;(j<=prime_index)&&(prime[j]<=limit);j++)
the first condition will be executed, but the result will be ignored.
So it is luck, that you find a number in the uninitialized array that is larger than limit before you go out of range of the array, which will lead to a SIGSEGV.
for(i=1;i<=prime_index,prime[i]<=limit;i++)
has the same problem.
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