C :

#include<stdio.h>
#include<math.h>
int main()
{
	int a,s,f,n;
	double i,j,t,q,r;
	n=1;
	f=1;
	q=0.0;
	t=1;
	scanf("%lf",&i);
	while(t>i)
	{
		t=(double)1/n;
		q=q+t*f;
		f=-f;
		n++;
		r=1/n;
		if(r<=i)
		{
			t=fabs(t);}
	}
	printf("%.4lf",q);

	return 0;
}

C++ :

#include<stdio.h>

int main()
{
	
	double e, a, b, c, d;
	scanf("%lf", &e);
	for(a = 1, c = 0, d = 1.0 ; ( 1 / a ) >= e  ; a++ )
	{
		b = d * (1 / a);
		c = c + b;
		d = -d;
	}
	printf("%.4lf", c);
	return 0;
}

Pascal :

program nghj;
var
  n,f:integer;
  s,e:real;
  begin
    readln(e);
    n:=1;
    s:=0;
    f:=-1;
    repeat
     f:=f*(-1);
     s:=s+(1/n*f);
     n:=n+1;

    until abs(1/(n-1))<=e;
    writeln(s:0:4);
end.