Using if statement for switch

function [success, Out_Torque] = convertTorque(In_Torque, UnoF, UnoL, DesF, DesL )

success=0;
Out_Torque=0;

forceconv=0;
lengthconv=0;

switch UnoF
   
    case "N"
        switch DesF
            case "N"
                forceconv= 1;
            case "lb"
                forceconv=(1/(0.453592 * 9.80665));
            case "oz"
                forceconv=(16/(0.453592 * 9.80665));
            case "kN"
                forceconv=(1/1000);
        end 

    case "kN"
        switch DesF
            case "N"
                forceconv= 1000;
            case "lb"
                forceconv= (1000/(0.453592 * 9.80665));
            case "oz"
                forceconv= 16 * (1000/(0.453592 * 9.80665));
            case "kN"
                forceconv= 1;
        end

    case "lb"
        switch DesF
            case "N"
                forceconv = (0.453592 * 9.80665);
            case "lb"
                forceconv = 1;
            case "oz"
                forceconv= 16;
            case "kN"
                forceconv= (0.453592 * 9.80665)/1000;
        end 
    case "oz"
        switch DesF
            case "N"
                forceconv = (0.453592 * 9.80665)/ 16;
            case "lb"
                forceconv = 1/16;
            case "oz"
                forceconv = 1;
            case "kN"
                forceconv= (0.453592 * 9.80665)/(16*1000);
        end 
end 


switch UnoL
    case "ft"
        switch DesL
            case "ft"
                lengthconv= 1;
            case "in"
                lengthconv= 12;
            case "mm"
                lengthconv= (12*25.4);
            case "m"
                lengthconv= (12*25.4)/1000;
        end
    case "in"
        switch DesL
            case "ft"
                lengthconv= 1/12;
            case "in"
                lengthconv= 1; 
            case "mm"
                lengthconv= 25.4;
            case "m"
                lengthconv= 25.4/1000;
        end 
    
    case "mm"
        switch DesL
            case "ft"
                lengthconv= 1/(12*25.4);
            case "in"
                lengthconv= 1/25.4;
            case "mm"
                lengthconv= 1;
            case "m"
                lengthconv= 1/1000;
        end 
    case "m"
        switch DesL
            case "ft"
                lengthconv= (1000/(12*25.4));
            case "in"
                lengthconv= (1000/ 25*4);
            case "mm"
                lengthconv= 1000; 
            case "m"
                lengthconv= 1;
        end 
end 

% if ((UnoF ~= "N" || "lb" || "oz" || "kN") || (UnoL ~= "ft" || "in" || "mm" || "m") )
%     Out_Torque=0;
%     success=0;
% end 

Out_Torque= In_Torque * forceconv * lengthconv;
success=1;

I'm having trouble creating a check for the input on my function. I want the function to return status=0 and Out_Torque= 0 if anything other than "N" "lb" "oz" "kN" is entered for Units of Force and likewise for "ft" "in" "mm" "m" for Units of Length.

The commented out part at the end is what I've been able to come up but it doesn't work and I know there's an easier way to do this.

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[DGM]

This is a simplified conceptual example of one way.

% define a list of valid strings
validforcestr = lower(["N" "lb" "oz" "kN"]);

% if this argument isn't valid, return with an error message stating why
if ~ismember(lower(Unof),validforcestr) 
    error('some error message about Unof')
end

You'd have to do similar for both force arguments and both length arguments. If you want it to be case-sensitive, omit the usage of lower().

If for some reason you want it to return null results without error, simply replace the error() call with output assignment and return.

% define a list of valid strings
validforcestr = lower(["N" "lb" "oz" "kN"]);

% if this argument isn't valid, return with an error message stating why
if ~ismember(lower(Unof),validforcestr) 
    Out_Torque = 0;
    success = 0;
    return;
end

Obviously, this has to happen before the main switch-case structure.

[Rahim Parvez]

When I try to implement the argument before the main switch-case structure, the function fails to run?

[DGM]

That's because the logical tests you were using don't work. This

if ((UnoF ~= "N" || "lb" || "oz" || "kN") || (UnoL ~= "ft" || "in" || "mm" || "m") )

is either true or will throw an error because this

UnoF ~= "N" || "lb" || "oz" || "kN"

is the same as this

(UnoF ~= "N") || "lb" || "oz" || "kN"

and "lb" is not a logical value, nor can it be interpreted as one.

Putting the input validation after the inputs are used defeats the purpose entirely.

[Rahim Parvez]

So how can I create an argument that recognizes "lb" as one of the few accepted answers of the input? Forgive my inexperience, MATLAB is still very new to me.

[DGM]

I already did. The example I gave above uses ismember() to check whether the specified argument matches one of the strings in the array called validforcestr.