Which type of variable is available throughout the entire program?

A global variable is a type of variable that is declared outside of all functions and is accessible from any part of the program. This means that once a global variable is created, it can be used in any function, allowing for easy data sharing among different parts of the program.

The significance of global variables lies in their scope; they have a program-wide reach, making them useful for storing information that should be accessible in multiple functions. However, it's important to use global variables judiciously, as excessive reliance on them can lead to code that is difficult to understand and maintain, especially in larger programs where many functions may alter the value of the global variable.

Local variables, in contrast, are defined within a specific function and cannot be accessed outside of that function's scope. Private and protected variables, commonly associated with object-oriented programming, pertain to the accessibility of attributes within classes, but these concepts do not apply to variables that are universally available across a program. Hence, global variables are the best fit for this context.