Change if -statement by userinput

Is it possible to change an if condition by a User input? E.g. I have a dropdown menu with the options ('<','>') and an if condition (if i>5 ....) I want to adapt my if-condition to the selected option in the dropdown menu. So if I choose '<' in the dropdown menu, my if condition changes from (if i>5 to if i<5).

Answer 1

[Stephen23]

Method one: use a cell array of function handles, and simply use the index from the menu to select which one you want:

idx = index of selection in menu, where 1='<' 2='>'
C = {@lt,@gt};
if C{idx}(i,5)
   ...
end

Method two: logical selection:

str = the selected string, either '<' or '>'
if strcmp(str,'>')&&(i>5) || strcmp(str,'<')&&(i<5)
    ...
end

[Matthias Berger]

Thank you a lot, the solution works just fine

[John K. George]

Hi Stephen,

Could you provide a more complete example? I am getting the following errors:

str = the selected string, either '<' or '>'

↑

Error: Invalid expression. Check for missing multiplication operator, missing or

unbalanced delimiters, or other syntax error. To construct matrices, use brackets

instead of parentheses.

[John K. George]

Thank you!

[Steven Lord]

A third approach, if you have a small fixed set of options:

% operator = input(['Enter the operator, either > or <, to be used ', ...
%    'in the comparison'], 's');
operator = '>'; % hard-coding this because you can't run INPUT in an Answers post
x = pi;
switch operator
    case '>'
        if x > 5
            disp('x is greater than 5.')
        else
            disp('x is not greater than 5.')
        end
    case '<'
        if x < 5
            disp('x is less than 5.')
        else
            disp('x is not less than 5.')
        end        
    otherwise
        error(['I asked for either > or < and you entered ', operator, '.'])
end

x is not greater than 5.