Which of the following function declaration is illegal?

In C, what is a function primarily used for?

A. Decision making

B. Variable declaration

C. Code organization and reusability

D. Printing output

What is the purpose of a function prototype in C?

A. To declare a function's return type

B. To declare a function's name

C. To declare a function's parameters and return type

D. To declare a function's name and parameters

What is the result of the expression sqrt(16) in C, assuming proper inclusion of the math library?

A. 4

B. 8

C. 2

D. Error

In C, how are function arguments passed by default?

A. By value

B. By reference

C. By pointer

D. By address