pi approximation using a series

Write a function that will use a series to calculate the value of π. Follow so many articles until the contribution of the last article is lower than 10^-4.Call the function and compare it with matlab function pi.

i tried it like this but it is far from correct.:

x=0;
sum=PI(x)
matlab=exp(x)

function [sum]=PI(x)
n=0;
N=(4*((-1)^i))/(2*i + 1);
sum=clen;
x=x+1;
while N>=10^(-4)
    n=n+1;
    N=(4*((-1)^i))/(2*i + 1);
    sum=sum+N;
end   
end

Answer 1

[KSSV]

x = 0 ;
n = 0 ; 
while ~(abs(pi-x) <= 10^-4 )
    x = x+4*(-1)^n/(2*n+1) ; 
    n = n+1 ; 
end

[Fe99]

Thanks!