#include <iostream.h>
#include <math.h>
#include <iomanip.h>
#include <stdlib.h>
 
void main()
{
    //program d6r5
    //driver for routine expdev
	int npts,i,j,idum;
	double y;
	double ee,trig[22], x[22],expect,total;
    npts = 10000; ee = 2.718281828;
    for (i = 1; i<=21; i++)
	{
        trig[i] = (i - 1) / 20.0;
        x[i] = 0.0;
    }
    idum = -1;
    for (i = 1; i<=npts; i++)
	{
        y = expdev(idum);
        for (j = 2; j<=21; j++)
		{
            if ((y < trig[j]) && (y > trig[j - 1])) 
			{
                x[j] = x[j] + 1.0;
			}
        }
    }
    total = 0.0;
    for (i = 2; i<=21; i++)
	{
        total = total + x[i];
    }
    cout<<"Exponential distribution with"<<npts<<"points;"<<endl;
    cout<<"      interval       observed    expected"<<endl;
    for (i = 2; i<=21; i++)
	{
        x[i] = x[i] / total;
        expect = exp(-(trig[i - 1] + trig[i]) / 2.0);
        expect = expect * 0.05 * ee / (ee - 1.0);  
	    cout<<setiosflags(ios::fixed);
		cout<<setprecision(2)<<setw(8)<<trig[i - 1];
        cout<<setprecision(2)<<setw(8)<<trig[i];
		cout<<setprecision(4)<<setw(12)<<x[i];
        cout<<setprecision(4)<<setw(12)<<expect<<endl;
	}
}