如果联合声明为[闭合],则不会显示循环

为什么 for 如果我包含 union test

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

union test{
    int intv;
    float floatv;
};

int main(){
    union test test1; // When this is removed the below loop displays.

    for(int i, j = 0; i < 5; i++, j = (j + i) * 2){
        printf("%d %d\n", i, j);
    }

    return 0;
}