or download this
C:\Users\Tony\dev\perl\git>gcc -Wformat -oint64.exe int64.c
int64.c: In function 'main':
int64.c:6:15: warning: format '%u' expects argument of type 'unsigned
+int', but argument 2 has type 'long long unsigned int' [-Wformat=]
...
int main() {
printf("%I64u\n", x);
}