How to convert this code to c++ in opencv?

clc;
clear;
disp('Rotate Operation');
disp('--------------------');
disp('input file name with the extension');
image= input('input image file = ');
citra=imread(image);
[n,m]=size(citra);
for x=1:n
  k=m;
  for y=1:m
      new_citra(k,x)=citra(x,y);
      k=k-1;
  end;   
end;
subplot(1,2,1),imshow(citra),title('Citra Gray');
subplot(1,2,2),imshow(new_citra),title('Citra Rotate 90');