Call by Value

• That last program, power changed i but nothing strange happened. This is because C is a call by value language: when you pass a function a variable, it gets only the variables' value, which is then put into a local variable. This local variable can then be freely changed, and it disappears when the function is done.

• Call by value is one way in which C encourages you to write functions without side effects, functions that don't change the programming enviornment except in returning a value.

• Two types of side effects we are already familiar with are
  • Changing a global variable from inside a function, and
  • Printing or getting input from inside a function.

• People don't like side effects because they violate our intuitive idea of what a function should be.