Matrix dimensions must agree. Error while using if.

     %example 
shape=input('What shape do you want?','s');
if shape=='square'
      side=input('What is the length of one side?');
      area=side^2;
      fprintf('The area is %f\n',area')
elseif shape=='rectangle'
      length=input('What is the length?');
      width=input('What is the width?');
      area=length*width;
      fprintf('The area is %f\n',area')
end

(after running the program it says:)

What shape do you want?rectangle
Matrix dimensions must agree.

Error in untitled (line 2) if shape=='square'

Answer 1

[Stephen23]

Use strcmp or strcmpi to compare the character vectors:

strcmpi(shape,'square')

Or switch:

switch lower(shape)
    case 'square'
        ...
    case 'rectangle'
        ...
end

When you use == on character vectors it performs an element-wise comparison, i.e. it compares like this:

shape(1)=='s'
shape(2)=='q'
shape(3)=='u'
...

and you can see the problem when it gets to the 'g' of 'rectangle':

shape(7)==???

because the sizes of the two vectors do NOT match, so this is an error.