Why do I get an error?

Hi I was writing a script for a program that ask the user to enter the material of an object and the surface's material to use the friction consent to find the force, and here is my script :

object=input('Enter the matiral of the object : ','s');
surface=input('Enter the matiral of the surface : ','s');
W=input('Enter weight : ');
U=[0.2 0.4 0; 0 0.35 0 ; 0 0 0.7];
%calculation_section
if object=='metal'
    OB=1;
elseif object=='wood'
    OB=2;
elseif object =='rubber'
    OB=3;
elseif surface=='metal'
    S=1;
elseif surface=='wood'
    S=2;
elseif surface=='concrete'
    S=3;
end
F=U(OB,S);
%output_section
disp(['The force is :',num2str(F)]);

The error i receive comes from different lines sometimes from this line OB=1; and sometimes from this line F=U(OB,S) each time I hit run it gives me a different error massage. I am stuck in this error for two days, I searched a lot but I couldn't fix it.I hope if you guys can help me.

[David Fletcher]

you should note that object=='metal' will not return a logical scaler: instead it returns a 1x5 logical vector correspnding to a match (or not) in each of the character positions. If the things you are testing are of a different lengths then you will get an error. Use a string comparison function instead

[Geoff Hayes]

See strcmp or strcmpi for details.

Answer 1

[Jan]

Instead of a bunch of if statements with strcmp, you can use switch also:

switch object
  case 'metal'
    OB = 1;
  case 'wood'
    OB = 2;
  case 'rubber'
    OB = 3;
  otherwise
    error('Unexpected object.')
end

switch surface
  case 'metal'
    S = 1;
  case 'wood'
    S = 2;
  case 'concrete'
    S = 3;
  otherwise
    error('Unexpected surface.')
end

In addition you need two different if or switch blocks. In your case after an object was found, the surface is not examined anymore.

Answer 2

[Eyad Alharbi]

thank you guys I tried strcmpi and it worked.