upcase.c

#include <stdio.h>
#include <string.h>

int main (int argc, char const *argv[])
{
    static char upcase[] =
        "\0______________________________"
        "_________________0123456789_____"
        "__ABCDEFGHIJKLMNOPQRSTUVWXYZ____"
        "__ABCDEFGHIJKLMNOPQRSTUVWXYZ____"
        "________________________________"
        "________________________________"
        "________________________________"
        "________________________________";
    
    char string[] = "hello world";
    
    for (int i = 0; i < strlen(string); i++) {
        string[i] = upcase[string[i]];
    }
    
    puts(string);
    
    return 0;
}