The toupper() function is used to convert lowercase alphabet to uppercase. i.e. If the character passed is a lowercase alphabet then the toupper() function converts a lowercase alphabet to an uppercase alphabet. It is defined in the ctype.

How do you use toupper?

The toupper() function converts the lowercase letter c to the corresponding uppercase letter. Both functions return the converted character. If the character c does not have a corresponding lowercase or uppercase character, the functions return c unchanged.

Which library is toupper in?

C library function - toupper()

The C library function int toupper(int c) converts lowercase letter to uppercase.