Can not print out the elements of an array in a for-loop

Question

Why can not I print out the elements of an array in a for-loop? My environment is Windows 7 Maximum, gcc (MinGW.org GCC-6.3.0-1) 6.3.0 I input the data from the prompt like 3 1 2 3. I can do, e.g., printf("%" PRId64 " ", marray[2]) but from the for-loop it doesn't work.

Here is the source code:

#define __USE_MINGW_ANSI_STDIO 1
#define __STDC_FORMAT_MACROS 1

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>

size_t read_size() {
    size_t x;
    scanf("%lu", &x);
    return x;
}

int64_t read_int64() {
    int64_t x;    
    scanf("%" SCNd64, &x);
    return x;
}

int main() {
    size_t *size;
    *size = read_size();
    int64_t *marray = malloc(sizeof(int64_t) * *size);
    for (size_t i = 0; i < *size; i++) {
        marray[i] = read_int64();
    }
        
    for (size_t i = 0; i < *size; i++) {
        printf("%" PRId64 " ", marray[i]);
    }
    free(marray);
    return 0;
}