# convert lower case to upper and upper to lower

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Lauren Kinchla on 21 Nov 2019
Edited: Jan on 21 Nov 2019
I need help writing a code to flip the case of the characters so that lower case are converted to upper case and upper case characters are converted to lower case and any number values remains unchanged

#### 1 Comment

Star Strider on 21 Nov 2019
There are MATLAB functions to do exactly that! This seems to be homework, so I will defer to you to explore the documentation.

Jan on 21 Nov 2019
Edited: Jan on 21 Nov 2019
You can use the function isstrprop with the category 'lower' and 'upper' to identify the specific characters. Then use the commands upper and lower to change the case.
An alternative is to use a comparison:
str = 'aSd12Bqm'
low = (str >= 'a' & str <= 'z')
high = (str >= 'A' & str <= 'Z')
Now upper and lower can be useful again. But you can try it with calculations of the ASCII code also:
str = 'a'
str2 = str + ('A' - 'a')
char(str2)
A smart trick is to flip the 5th bit of the ASCII representation, if the character is a letter:
str = 'Aa'
char(bitxor(double(str), 32))
% 'aA'
% Coversion to DOUBLE is needed, because BITXOR cannot operate on CHARs
You have to use a mask to affect the letters only. See the creation of low and high above, which can be combined.
See:
doc char
doc isstrprop
doc lower