Global Variable

A local variable is declared inside a procedure or function and is available only within that routine. A global variable is declared outside all routines and is available throughout the program, including inside the routines. A routine's parameters behave as local variables too. Local variables are preferred because they cannot be changed by accident from somewhere else in the program, which makes a routine easier to test on its own; too many globals make a program harder to understand, harder to test and harder to change safely.