C语言怎么实现matlab定义的空矩阵

简单的说怎么实现上面图片显示的功能？主要困扰我的就是怎么实现空矩阵，，，把矩阵赋值为NULL，显示的是0；如果只是开辟内存空间不赋值，显示的又是随机数。怎么解决啊？

#include
#include
#include
#include

void main()////
{
int M,M1,**M2;
int i, j,y;

M = (int **)malloc(sizeof(int *));
for (i = 0; i < 1;i++)
{
    for (j = 0; j < 3; j++)
    {
        *(M + i) = (double *)malloc(sizeof(double) * 3);
    }
}
for (i = 0; i < 3;i++)
{
    M[0][i] = 1;
}
scanf("%d", &y);

if (y>5)
{  //如何定义M1为空矩阵
    /*M1 = (int **)malloc(sizeof(int *));
    for (i = 0; i < 1; i++)
    {
        for (j = 0; j < 3; j++)
        {
            *(M1 + i) = (double *)malloc(sizeof(double) * 3);
        }
    }
    for (i = 0; i < 3; i++)
    {
        M1[0][i] = NULL;
    }*/
}
else
{
    M1= (int **)malloc(sizeof(int *));
    for (j = 0; j < 3; j++)
    {
        *M1 = (double *)malloc(sizeof(double) * 3);
    }

    for (i = 0; i < 3; i++)
    {
        M1[0][i] = 2;
    }

}
M2 = (int **)malloc(sizeof(int *) * 2);
for (i = 0; i < 2; i++)
{
    for (j = 0; j < 3; j++)
    {
        *(M2 + i) = (double *)malloc(sizeof(double) * 3);
    }
}
for (j = 0; j < 3; j++)
{
    M2[0][j] = M[0][j];
}

for (j = 0; j < 3; j++)
{
    M2[1][j] = M1[0][j];
}

//输出：
for (i = 0; i < 2; i++)
{
    for (j = 0; j < 3; j++)
    {
        printf("%d\t", M2[i][j]);
    }
    printf("\n");
}

}

我需要的是输入6的话 显示的是1 1 1