CODEWITHSUNDEEP
matlab
user8717568
user8717568

Reputation: 11

Numbers on telephone to letters. 2=ABC 3=DEF etc. Using switch case but code isnt giving desired results. How would I return the code as asked below

for var=1:length(str)
switch str(var)
   case {'A':'C'}
     disp('2')
   case {'D':'F'}
     disp('3')
   case {'G':'I'}
     disp('4')
   case {'J':'L'}
     disp('5')
   case {'M':'O'}
     disp('6')
   case {'P' 'R' 'S'}
     disp('7')
   case {'T':'V'}
     disp('8')
   case {'W':'Y'}
     disp('9')
end

I am using this code in trying to make a statement such as ('1-800-TO-WELLS') become '1-800-86-93557', but the output is "str=1-800-TO-WELLS and 7". Any amount of tips and help is very appreciated. If I haven't provided a valid enough question please leave comments so I can improve.

Upvotes: 1

Views: 232

Answers (2)

gnovice
gnovice

Reputation: 125874

Troy gives a very clear answer as to why your code isn't working: {'A':'C'} results in a 1-element cell array {'ABC'}, but you want to use a 3-element cell array {'A' 'B' 'C'} since the way the switch compares case expressions will result in a match if one cell element exactly matches a given character.

As an alternative to using a for loop and switch statement, you could also do this using the ismember function and some indexing:

% Character/number map and test string:
map = ['ABCDEFGHIJKLMNOPRSTUVWXY'; '222333444555666777888999'];
str = '1-800-TO-WELLS';

% Convert test string:
[isInMap, index] = ismember(str, map(1, :));
str(isInMap) = map(2, index(isInMap));

And the result:

str =

1-800-86-93557

Upvotes: 1

TroyHaskin
TroyHaskin

Reputation: 8401

For strings, the cases in the switch block act like calls to strcmp, so case <caseExpression> is true if any(strcmp(<caseExpression>,<switchExpression>)).

This is important because {'P' 'R' 'S'} and {'P':'S'} do not generate the same output:

>> {'P' 'R' 'S'}
ans = 
    'P'    'R'    'S'
>> {'P':'S'}
ans = 
    'PQRS'

The first is a 1-by-3 cell array with individual characters as the elements' contents; the second is a 1-by-1 cell array with a 1-by-4 character array as the element's content. Performing a strcmp on the first one will give true if the <switchExpression> is a letter in the set while the second will only give a true if <switchExpression> is exactly 'PQRS':

>> strcmp({'P' 'R' 'S'},'S')
ans =
     0     0     1
>> strcmp({'P':'S'},'S')
ans =
     0
>> strcmp({'P':'S'},'P':'S')
ans =
     1

So the 7 pops out because its case is the only one that gives true when given a matching character.

As a side note, you may consider using the otherwise statement to echo non-matching characters:

switch str(var)
.
.
.
    otherwise
        disp(str(var));
end

Upvotes: 2

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