How do I use characters with an if statement?

My code looks like this

Prompt='Please press any key to roll the dice, press Q or q to quit program: ';
str=input(Prompt, 's');
if str == q||Q
    fprintf('program terminated')
end

end

Essentially what I want to do is if the user inputs Q, the fprintf statement is true. However, I'm unsure of how to do this, as it only see's q as an unrecognized value

Answer 1

[Jan]

Prompt = 'Please press any key to roll the dice, press Q or q to quit program: ';
str    = input(Prompt, 's');
if strncmpi(str, 'q', 1)
    fprintf('program terminated')
end

strncmpi compares the given number of characters ignoring the case. This is nicer than:

if ~isempty(str) && str(1) == 'q' || str(1) == 'Q'    

or

if ~isempty(str) && lower(str(1)) == 'q'    

[Ishana Alviar]

why does it need to have 's' ?

[Adam Danz]

See documentation,

str = input(prompt,'s')

Answer 2

[Adam Danz]

If you want to consider case (assuming str, q, and Q are all strings or character arrays)

if any(strcmp(str, {q,Q})) % [q,Q] for string arrays

or

if ismember(str, {q,Q}) % [q,Q] for string arrays

If you want to ignore case

if any(strcmpi(str, {q,Q})) % [q,Q] for string arrays

or

if ismember(lower(str), lower({q,Q})) % [q,Q] for string arrays

[Rik]

I suspect q and Q were meant as literal characters, not variables.

[Adam Danz]

@John Jamieson In that case (see Rik's comment above), {q,Q} would be {'q','Q'} or ["q","Q"] for strings.

Also, just a public service announcement, when using input() you should include input validation. For example,

if you're expecting a single character,

assert(numel(str)==1, 'Input must be 1 character.')

if you're expecting a word with no spaces,

assert(any(isspace(str)), 'Input must not contain spaces.')

if you're expecting only letters and no numbers,

assert(all(isletter(str)),'Input must only be letters')

etc....