为什么我们需要在c中同时初始化或声明两个维度​​而不是一个接一个地

Question

int a[3][3] = { {1, 2, 3} , {4, 5, 6} , {7, 8, 9} };

Is working

int a[3][3] ;
a[3][3] = { {1, 2, 3} , {4, 5, 6} , {7, 8, 9} 

Is not working . It shows and error in my gcc compiler

Answer 1

The first line of code is declaring the array and defining the entire contents . What you're saying here is "create a 3x3 array of integers with these contents."

When you write:

int a[3][3];

What you're saying is, "create a 3x3 array of integers." You're not specifying the contents.

Your second example has two problems.

First, arrays are 0-based, so a[3][3] doesn't exist. The valid indexes are 0, 1, and 2.

More importantly, when you address a[x][y] , you're addressing that specific cell . In other words, "assign a value to cell [2][2] in the array."

So a[2][2] = 42; is valid. But you can't assign an array to a[2][2] because it only holds one integer.