程序接收信号SIGSEGV，输出分段故障

我在调试程序时遇到了这个奇怪的错误（程序接收到信号SIGSEGV，Segmentation fault->，指向下面的代码行）。求你了，真的需要你的帮助。我试图设置一些"if"条件，以处理构造函数和析构函数中的"负"初始化值。

class a
{
public:
    a(int _number1=0, float* _array1=NULL);
    ~a();
    friend ostream& operator<<(ostream& output1, a& all_1);
private:
    int number1;
    float* array1;
};
class b
{
public:
    b(int _number2=0, float* _array2=NULL);
    ~b();
    friend ostream& operator<<(ostream& output2, b& all_2);
private:
    int number2;
    float* array2;
};
a::a(int _number1, float* _array1)
{
    if(_number1>0)
    {
        number1 = _number1;
        array1 = new float[number1];
        memset(array1, 0, number1*sizeof(float));
    }
    else array1=_array1;
}
a::~a()
{
    if(number1>0) delete[] array1;
}
ostream& operator<<(ostream& output1, a& all_1)
{
    if(all_1.number1>0)
    {
        for(int i=0;i<all_1.number1;i++) output1<<all_1.array1[i]<<"n";
    }
    else output1<<"";
    return(output1);
}
b::b(int _number2, float* _array2)
{
    if(_number2>0)
    {
        number2 = _number2;
        array2 = new float[number2];
        memset(array2, 0, number2*sizeof(float));
    }
    else array2=_array2;
}
b::~b()
{
    if(number2>0) delete[] array2;
}
ostream& operator<<(ostream& output2, b& all_2)
{
    if(all_2.number2>0)
    {
        for(int i=0;i<all_2.number2;i++) output2<<all_2.array2[i]<<"n"; //This is where the error appeared.
    }
    else output2<<"";
    return(output2);
}
int main()
{
    a input1(-1);
    b input_1(-1);
    cout<<input1;
    cout<<input_1;
}