编辑：刚注意到您正在使用C ++。在这种情况下，std :: vector绝对是最方便的解决方案。如果您对如何使用C风格的普通数组感到好奇，请继续阅读...

Edit: Just noticed you are using C++. In this case, std::vector is definitely the most convenient solution. If you are curious about how to do this with plain arrays, C style, then read on...

您可以不要这样您需要做的是创建一个3维数组（或2维数组，具体取决于您的观点...）

You can't do it like this. What you need to do is create a 3 dimensional array (or an array of 2-dimensional arrays, depending on your point of view...)

在C的情况下，内存分配很麻烦...您可以静态分配：

As is always the case with C, memory allocation is a pain... You can statically allocate:

long double x[N][size][size];

（N是在编译时确定的。请确保它足够大。
也如果N确实很大，则可以声明数组（可以作为全局变量，也可以使用 static 关键字）。否则，可能会导致堆栈溢出。）

(N is determined at compile time. Make sure you have it large enough. Also if N is really big, declare the array stactically (either as a global variable or with the static keyword). If you don't you can get a stack-overflow.)

或者您可以使用动态内存分配：

Or you can use dynamic memory allocation:

long double (*x)[size][size]; // x is a pointer to size by size arrays
x = malloc(n * sizeof(*x));
//You can now use x[j][a][b]...

也许使用typedef看起来会更好（即使我不是100％肯定在上一个示例中也得到了数组声明...）：

Maybe things look better with a typedef (even I am not 100% sure I got that array ceclaration right in the last example...):

typedef long double typename_here[size][size];
typename_here *x;
x = malloc(n * sizeof(typename_here);

顺便说一句，您当前的代码不起作用的原因是

BTW, the reason your current code doesn't work is

1. x（j）语法是虚构的：）


2. 在循环内声明的变量在该块的内部。这意味着您不能在循环正文之后访问它们。

1. The x(j) syntax is ficticious :)
2. Variables declared inside a loop are internal to that block. This means you can't access them after the loop body.