程序代码：

#include <stdio.h>
#include <math.h>
double sqrt (double x)
{
double Epplion = 1E-5;
double  Guessnum = 1.0;
if(x > 0.0) {
while (fabs (Guessnum * Guessnum - fabs (x)) >= Epplion)
{
    Guessnum = ( fabs (x) / Guessnum + Guessnum) / 2.0;
}
return Guessnum;
}
else if (x == 0.0) return 0.0;
else exit (0);
}
main ()
{
    double x;
    scanf ("%lf",&x);
    printf ("%lf\t",sqrt (x));
    getch ();
    return 0;
    }