toupper

From cppreference.com
< c‎ | string‎ | byte
Defined in header <ctype.h>
int toupper( int ch );

Converts the given character to uppercase according to the character conversion rules defined by the currently installed C locale.

In the default "C" locale, the following lowercase letters abcdefghijklmnopqrstuvwxyz are replaced with respective uppercase letters ABCDEFGHIJKLMNOPQRSTUVWXYZ.

Parameters

ch - character to be converted. If the value of ch is not representable as unsigned char and does not equal EOF, the behavior is undefined.

Return value

Uppercase version of ch or unmodified ch if no uppercase version is listed in the current C locale.