Explain the differences between a parameter, a local variable, and a local static variable. Give an example of a function in which each might be useful

A **local variable** is a variable defined inside the function scope.

  - The scope of a local variable is the function body.

  - The lifetime of the ordinary local variable (non`static`) starts when control passes through the variable's definition, and ends when control passes through the end of the block in which the variable is defined.

  - It is initialized if its definition contains an initializer, otherwise, it is default initialized.

A **parameter** is also a local variable, but the definition is in the parameter list of the function.

  - The scope of a parameter is the same as local variable, which is the function body.

  - The lifetime of the parameter starts when the function begins, and ends when the function terminates.

  - It is initialized by the arguments passed to the function.

A **local `static` variable** is a local variable that defined with `static` keyword. It has a lifetime much longer than usual local variable.

  - The scope of a local `static` variable is the same as local variable, which is the function body.

  - The lifetime of the local static varible starts when the *first* time control passes through the variable's definition, and ends when the *program* terminates.

  - It is initialized if its definition contains an initializer, otherwise, it is value initialized.

For example,

    int foo(int param) {
      int lv;
      static int lsv = 1;
      lv = param + lsv;
      ++lsv;
      return lv;
    }

every time the function `foo` is called, it will add how many times it has been called to the argument and return the sum.