C language reference manual

C Standard Library <ctype.h>

C library function toupper() usage and example

If the parameter passed is a lowercase letter, the toupper() function will convert the lowercase letter to uppercase.

C toupper() function prototype

int toupper(int arg);

The toupper() function accepts a single parameter in integer form and returns an int type value.

Even if toupper() uses an integer as a parameter, the character is still passed to the function. Internally, the character is converted to the corresponding ASCII value for checking.

If the parameter passed is not a lowercase letter, it returns the same character passed to the function.It<ctype.h>

Defined in header files.

Example: C toupper() function
#include <stdio.h>
#include <ctype.h>
int main()
　　　　{
　　　　char c;
　　　　c = 'm';　->　%c", c, toupper(c));
　　　　//If the character passed to toupper() is not a lowercase character, it displays the same parameter passed.
　　　　c = 'D';
　　　　printf("\n%c　->　%c", c, toupper(c));
　　　　c = '9';
　　　　printf("\n%c　->　%c", c, toupper(c));
　　　　return 0;
}

Output Result

m　->　M
D　->　D
9　->　9

C Standard Library <ctype.h>