How to use toupper on char * in C?

So I have a problem with using toupper on char *. Let me show you what I tried.

#include <stdio.h>
#include <ctype.h>
#include <string.h>
int main() {
    char* shi = command->args[0]; //which is "binance"

    while(*shi) {
        toupper((unsigned char) *shi);
        shi++;
    
    }

    printf("Capitalized version is: %s",shi); // which should be "BINANCE".

return 0;
}

This statement

toupper((unsigned char) *shi);

has no effect. The result of the call of toupper is not used.

Also after this while loop

while(*shi) {
    toupper((unsigned char) *shi);
    shi++;

}

the pointer shi points to the terminating character '\0' of the string.. So the following call of printf

printf("Capitalized version is: %s",shi);

will deal with an empty string.

You should write for example

for ( char *p = shi; *p; ++p ) {
    *p = toupper((unsigned char) *p);
}