const char *str = "level";
//a string ends with the zero character
for (const char *p = str; *p != '\0'; p++) {
putchar(*p);
}
putchar('\n');
//strlen walks the whole string: call it once, not in the condition
size_t length = strlen(str);
for (size_t i = 0; i < length; i++) {
printf("str[%zu] = %c\n", i, str[i]);
}