.............................
program 20
..............................
#include<stdio.h>
#include<math.h>
#define PREC 0.0000001
main()
{
	double x_old,x_new,z,f;
	int i,j,k;
	scanf("%lf",&z);
	x_old = 0;
	x_new = 1;
	i = 0;
	f = 1;
	while( fabs((x_old-x_new)/x_old) > PREC){
          x_old = x_new;
	  ++i;
          f *= i;
	  x_new += pow(z,i)/f;
	  printf("%d  %15.12f  %15.12f\n",i,x_new,exp(z));
	}
}

..................................
program 21
..................................
#include<stdio.h>
main()
{
  double y,sum;
  int n;

  n = 0;
  sum = 0;
  while(scanf("%lf",&y) != EOF){
    ++n
    sum += y;
  } 

  printf("number of data= %d\n",n);
  printf("average= %f\n",sum/n);
}

......................................
program 22
......................................
#include<stdio.h>
main()
{
  int x1,x2;
  int n,m,q;

  scanf("%d",&x1);
  scanf("%d",&x2);

  if(x1 >= x2) {n = x1; m = x2;}
  else {n = x2; m = x1;}

  while( (q = n % m) > 0) {
    n = m;
    m = q;
  }

  printf("%d\n",m);
}