How to use if statement to add if negative and minus if positive

I am trying to write an if statement to add 180 if the value is negative, and minus 180 if the value is positive. I have tried the below script and it does not work! I do not know how to fix this, and was hoping someone might have an idea? get a bit stick on if statements so find it difficult to problem solve! I have also attached the bit of code beforehand for context

%% Zeros to NaN
P5LANK=PLANK;
P5LANK(P5LANK==0) = NaN;

%% Unwrap so doesn't jump at 180 degrees
P5LANK_unwrap=unwrap(P5LANK*pi/180)*180/pi;
[m,n] = size(P5LANK_unwrap);

%% Interpolate

[Ny,Nx] = size(P5LANK_unwrap);
Nz = sum(~isnan(P5LANK_unwrap));                          % Determine number of non-NaN
for k = 1:Nx
    P5LANK_interp(:,k) = interp1(1:Nz(k),P5LANK_unwrap(1:Nz(k),k),1:Ny,'linear','extrap');    
end

%% Minus 180

for k = 1:Nx
if 
    P5LANK_interp(:,k) > 0
    P5LANK_minus180 = P5LANK_interp(:,k) - 180;
else
    P5LANK_minus180 = P5LANK_interp(:,k) + 180;
end

[Torsten]

You know that

P5LANK_interp(:,k) > 0

is only true if all elements in the k-th column are >0 ?

[Stephen23]

Perhaps MOD does what you want.

Answer 1

[dpb]

PM180=P-sign(P)*180;