How to make a sum series using a for loop

Given the power series of sin(x) I have to create a function that takes in x vector and N (number of terms in the sequence) and outputs the power series approximation of pi at that N. I cannot use any trig command or any sum command in the answer. I have written this code so far, which says that the sum= the first term (which would be x) plus the k'th term in the sequence. My problem is that MatLab keeps printing out the x value as the answer instead of the sum. How can I fix this code to make it so that MatLab prints out the sum.

for k=1:N
    s=x+((-1)^k)*((x^(2*k+1))/factorial(2*k+1));
end

Answer 1

[Geoff Hayes]

Petch - in your code, you are assigning the kth iteration value (plus x) to s rather than summing all values. Try instead

s = x;
for k=1:N
    s = s + ((-1)^k)*((x^(2*k+1))/factorial(2*k+1));
end