Code Golf: Leibniz Series

Question

This is the same question as Solve the CodeSprint4 Leibniz code golf challenge in Python in 66 characters. The variation is that I'm a C programmer. My code for the above question is:

#include <math.h>
main(){  
int i,t,p;  
scanf("%d",&t);  
while(t--)  
{  
double s=1;  
scanf("%d",&p);  
for(i=1;i<p;++i)  
s+=pow(-1,i)/(2*i+1);  
printf("%.12lf\n",s);  
}  
} 

Now I just need to know the places where I could reduce my code length.

Answer 1

1. Do everything in one line.
2. Don't read number of test cases, scanf will return -1 on EOF
3. Don't include anything, pow(-1,i) can be replaced by 1-i%2*2
4. Do the sum loop in reverse to save a variable.

Here is my 102 bytes code

main(n){gets(&n);for(double s;s=scanf("%d",&n)>0;printf("%.15f\n",s))while(--n)s+=(1-n%2*2)/(1.+2*n);}

Answer 2

Remove include and replace pow by check.
Use the fact that scanf returns number of read and saved fields.
Replace while via for.
Remove figure brackets.
Use %f in printf for double - only scanf needs %lf.

I didn't check if following code works fine, but even if smth is wrong, the correct result have to be somewhere near it:

main(){  
int i,t,p;
double s;
for(scanf("%d",&t);t--;printf("%.12f\n",s))
for(s=i=scanf("%d",&p);i<p;++i)  
s+=(i&1?-1:1)/(2.*i+1);  
}

By the way, what about making all variables double instead of int?