Ascii to lower / upper

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

int main(void) {
    char text[8] = "Hell^23o";
    size_t len = strlen(text);
    
    uint64_t mask = 0;
    for (size_t i = 0; i < 8; ++i) {
        if ((text[i] >= 'a' && text[i] <= 'z') || (text[i] >= 'A' && text[i] <= 'Z'))
            mask |= (size_t)0x20 << (i * 8);
    }
    
    *(uint64_t *)&text &= ~mask;
    printf("Upper: %.8s\n", text);
    
    *(uint64_t *)&text |= mask;
    if (len < 8) {
        text[len] = 0;
    }
    printf("Lower: %.8s\n", text);
    
    return 0;
}