External variable initialization and constant expressions

Code:

# Include <stdio. h> # include <stdlib. h> // External Storage Class: type with File Scope, external links, and static storage period // external variables ): int A, a variable with an external storage class; // if the external variable is not explicitly initialized, the initial value 0int B is automatically assigned; int ages [10]; // The file scope variable can only be initialized using a constant expression // as long as it is not a variable-length array, the sizeof expression is considered a constant expression int Len = 20; int d = sizeof (INT) * 5; // The sizeof expression below is not a constant expression // sizeof (INT [Len]) * 5int main (void) {return exit_success ;}

External variable initialization and constant expressions