Switch case with strings?

I'm trying to create a loop which takes the name of a regular polygon from the user. It should be case insensitive and the program should have cases for a pentagon, hexagon, heptagon, octagon, and nonagon all with fixed side length 10 (I have precalculated the areas, I just want the program to output the numbers I give it). If a typo is made or the user inputs an unrecognized shape name, the program should output an error message and run the loop again. The user is supposed to have 3 chances to type a shape name correctly before the program terminates, and if they always type one correctly, the loop should run infinitely.

This is all I have so far, and it's not working:

if true
  t=input('Enter shape name: ');
ShapeName=char(t);
switch ShapeName
  case char('pentagon')
      fprintf('The area of the pentagon is 172.05 m^2.')
  case char('hexagon')
      fprintf('The area of the hexagon is 259.81 m^2.')
  case char('heptagon')
      fprintf('The area of the heptagon is 363.39 m^2.')
  case char('octagon')
      fprintf('The area of the octagon is 482.84 m^2.')
  case char('nonagon')
      fprintf('The area of the nonagon is 618.18 m^2.')
  otherwise
      disp('Error, no such shape is found! Try again!') 
end
end

Please help! I'm totally lost.

Answer 1

[sixwwwwww]

Dear Shannon, maybe you can do as follows:

count = 0;
while count < 3
    ShapeName = input('Enter shape name: ', 's');
    switch ShapeName
        case 'pentagon'
            fprintf('The area of the pentagon is 172.05 m^2.\n')
            count = 0;
        case 'hexagon'
            fprintf('The area of the hexagon is 259.81 m^2.\n')
            count = 0;
        case 'heptagon'
            fprintf('The area of the heptagon is 363.39 m^2.\n')
            count = 0;
        case 'octagon'
            fprintf('The area of the octagon is 482.84 m^2.\n')
            count = 0;
        case 'nonagon'
            fprintf('The area of the nonagon is 618.18 m^2.\n')
            count = 0;
        otherwise
            fprintf('Error, no such shape is found! Try again!\n')
            count = count + 1;
    end
end

I hope it helps. Good luck!

[Shannon]

Thank you, that helped a lot!

Now I'm trying to get the program to display "Error, no such shape is found! Program terminated." after the 2nd over all error. For example, the user could input:

if true
  Enter shape name: "Pentagon" 
>>The area of the pentagon is 172.05 m^2.
Enter shape name: "heCagon"
>>Error, no such shape is found! Try again!
Enter shape name: "octagon"
>>The area of the octagon is 363.39 m^2.
Enter shape name: "noTagon"
>>Error, no such shape is found! Program terminated.
end

Do you happen to know how I could get this to work without using if/elseif?

[sixwwwwww]

You can do it as follows:

count = 0;
ErrorMsg = {'Error, no such shape is found! Try again!', 'Error, no such shape is found! Program terminated.'};
while count < 2
    ShapeName = input('Enter shape name: ', 's');
    switch ShapeName
        case 'pentagon'
            fprintf('The area of the pentagon is 172.05 m^2.\n')
        case 'hexagon'
            fprintf('The area of the hexagon is 259.81 m^2.\n')
        case 'heptagon'
            fprintf('The area of the heptagon is 363.39 m^2.\n')
        case 'octagon'
            fprintf('The area of the octagon is 482.84 m^2.\n')
        case 'nonagon'
            fprintf('The area of the nonagon is 618.18 m^2.\n')
        otherwise
            fprintf('%s\n', ErrorMsg{count + 1});
            count = count + 1;
    end
end

Good luck!

[Mitch Lautigar]

count = 0;
ErrorMsg = {'Error, no such shape is found! Try again!', 'Error, no such shape is found! Program terminated.'};
while count < 2
    ShapeName = input('Enter shape name: ', 's');
    switch ShapeName
        case (strcmpi(ShapeName,'pentagon')==1)
            fprintf('The area of the pentagon is 172.05 m^2.\n')
        case (strcmpi(ShapeName,'hexagon')==1)
            fprintf('The area of the hexagon is 259.81 m^2.\n')
        case (strcmpi(ShapeName,'heptatagon')==1)
            fprintf('The area of the heptagon is 363.39 m^2.\n')
        case (strcmpi(ShapeName,'octatagon')==1)
            fprintf('The area of the octagon is 482.84 m^2.\n')
        case (strcmpi(ShapeName,'nontagon')==1)
            fprintf('The area of the nonagon is 618.18 m^2.\n')
        otherwise
            fprintf('%s\n', ErrorMsg{count + 1});
            count = count + 1;
    end
end

strcmpi() compares two string inputs without caring about case. I haven't run this code, and i know this question is from 2013, but maybe it'll help someone else in the future.

[Steven Lord]

If you want the switch / case not to take case into account, switch on lower(ShapeName).

[Walter Roberson]

Mitch, the cases that you use in switch need to be a compatible datatype with the switch expression. You are switching on a character vector, but your cases are all logical. You would need

count = 0;
ErrorMsg = {'Error, no such shape is found! Try again!', 'Error, no such shape is found! Program terminated.'};
while count < 2
    ShapeName = input('Enter shape name: ', 's');
    switch true
        case (strcmpi(ShapeName,'pentagon')==1)
            fprintf('The area of the pentagon is 172.05 m^2.\n')
        case (strcmpi(ShapeName,'hexagon')==1)
            fprintf('The area of the hexagon is 259.81 m^2.\n')
        case (strcmpi(ShapeName,'heptatagon')==1)
            fprintf('The area of the heptagon is 363.39 m^2.\n')
        case (strcmpi(ShapeName,'octatagon')==1)
            fprintf('The area of the octagon is 482.84 m^2.\n')
        case (strcmpi(ShapeName,'nontagon')==1)
            fprintf('The area of the nonagon is 618.18 m^2.\n')
        otherwise
            fprintf('%s\n', ErrorMsg{count + 1});
            count = count + 1;
    end
end

which is ugly but legal.

Steven's recommendation to switch on lower(ShapeName) is much better coding.