help on c programming involving taylor series

Create a program that will approximate the error function erf(x) and erfc(x). Use the following Taylor series expansion:

http://i49.photobucket.com/albums/f2...r/untitled.jpg

Code:

Restrictions:

1. Use at most 6 variables in the main function.

2. Create a separate function for power using recursion.

3. Create a separate function for factorial using iteration.

4. Calculate the approximation until the 100th term of the Taylor series and print out approximation up to 4 decimal places.

*I have accomplished numbers 2 and 3.

2.)

int power(int b, int e){

if(b==0 && e==0){

printf("Invalid.\n");

main();

}

if(e==1){

return b;

}

if(e==0){

return 1;

}

else{

return b*power(b,e-1);

}

}

3.)

double factorial(double value){

int ctr;

double fact;

if(fact<0){

printf("Invalid.\n");

main();

}

else{

fact=1;

for(ctr=1;ctr<=value;ctr++){

fact*=ctr;

}

return fact;

}

}

***Any help will be appreciated. Thanks!