I am using the CS50 appliance from Harvard and trying to make a character lowercase. I am trying to use the tolower() function but when I try to use it I get the message implicit declaration of function 'tolower' is invalid in C99. Anyone care to elaborate on why I would be getting this message. I have included stdio.h as well as string.h.
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Jonathan Leffler
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ChapmIndustries
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1You didn't include the header and, in C99, functions are not assumed to be valid and return an int if there is no definition. – Ed S. Sep 27 '12 at 03:21
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To use tolower in C99, use #include <ctype.h>
It is not an I/O function and it doesn't operate on strings (it operates on characters), so it's not in stdio or string.
Gabe
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Well this has corrected the problem of calling an unidentified function but now when I try to just say `character[0]="A";` i get trouble. Any ideas? Says something about pointers and integers. For reference I declared `char character[2];`. – ChapmIndustries Sep 27 '12 at 03:22
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2character[0] = 'A' should work. By doing character[0] = "A", you are trying to assign a string to a character, which is not allowed. – Jay Sep 27 '12 at 03:25
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@ChapmIndustries "A" is `const char *`, so the assignment is dealign with `const char *`, a pointer type, assigned to `char`, an integral type. – obataku Sep 27 '12 at 03:48
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tolower is defined in ctype.h. That is the file you should be including:
#include <ctype.h>
will solve your problem.
epsalon
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