Programming Forums - strange problem of compiling

Hi ,
I urgently need help . I make a program that compute the area of triangle.
When I run my program on my computer everything is OK. But when I run it on the school system I get this
compilation error:

ld:
Unresolved:
sqrt

My function is fixed ..I mean the argument types have been imposed.
Please can someone help me I just have few hours left.

#include<iostream>

#include<cmath>

#include<ctime>

#include<cstdlib>



using namespace std;



void compute_area(double&,double&,double,double,double);



int main()

{

    double area,perimeter;

    double a,b,c;



 

    cout<<"Enter length a: ";

    cin>>a;

    cout<<endl;



    cout<<"Enter length b: ";

    cin>>b;

    cout<<endl;



    cout<<"Enter length c: ";

    cin>>c;

    cout<<endl;

    

    compute_area(area,perimeter,a,b,c);

    

  return 0;

}//end main





void compute_area (double& area, double& perimeter, double a, double b,

double c)

{   

    double s;

    //s=0;



    if( (a>(b+c))||(b>(a+c))||(c>(b+a)) )

     {   cout<<"bad combination!"<<endl;

         return;

      }



    else

     {

         s = (a + b + c)/ 2.0;

         area = sqrt (s*(s-a)*(s-b)*(s-c));

         perimeter=a+b+c;

         cout << "The area of a triangle with sides of length " << a

         << ", " << b << " and " << c << " is " << area <<

         " and its perimeter is "<<perimeter<< endl;

         return;

     }   

}

Thank you