##### Synopsis

    #include <ctype.h>
    int toupper(int c);

##### Description

toupper converts a lowercase letter to a corresponding uppercase letter.
If the argument c is a character for which islower is true, toupper returns the corresponding uppercase letter; otherwise, the argument is returned unchanged.

##### Portability

toupper conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).