I don't think you need an if statement or a for loop. Here is one way to do it:
X = 30 % Sample starting number.
while X < -pi
% Add multiples of 2*pi to X until the result is between [-pi, pi)
X = X + 2 * pi
end
while X > pi
% Subtract multiples of 2*pi until the result is between [-pi, pi)
X = X - 2 * pi
end
The code works and you don't need an if to check the value of X beforehand.
