When defining an array, the size must be constant

Sometimes we need to dynamically determine the size of the array , The following methods may be adopted ：

int n=5;

int a[n];

Be careful ： The above definition is wrong , Because when defining an array , The size of the array must be explicitly determined , Such as int a[5], The size of the array must be a constant , In this way, the compiler can allocate a certain and accurate space to the data .

It can be understood in this way ：

1. When defining an array, the allocation of memory is already involved , If the compiler finds that the size of the array is not given directly when allocating space to the array , It's a variable , If this variable is not initialized , The system randomly assigns a value , The size of the array is also uncertain .

2. If you want to dynamically allocate the array size according to your needs , Use pointer +malloc Methods , Dynamically allocate an array in the heap , Use a pointer to access this array , Is a more flexible way .

summary ： When defining an array , Be sure to specify the specific size of the array , Otherwise, some compilers will report errors , such as vs.