Function Calls

• Functions are small bits of code that can be called anywhere in the code.
  • Function usually solve small problems.
  • They can take input
  • They can produce output
• The math library provides a set of functions
• Let's look at the square root function.
  • reference
  • First, we see that it has changed over the years.
  • C++11 and beyond it needs #include < cmath>
  • It takes a single parameter or input value.
  • It returns a single value.
• Note a function prototype
  • double sqrt (double x);
  • Lists the return type
  • The function name.
  • At least the types of any parameters or arguments.
• The standard library supplies a large number of functions.
  • If you need a function, searching is probably the best way to find it.
  • Beware you might need to add a library for some.
  • a list
  • Memorizing all of the math functions is not a good idea.
• Our author discusses several functions
  • int abs(int)
  • float fabs(float)
  • double cos(double)
    • (but float, long double, ...
    • the angle is expected to be in radians
    • But M_PI is a constant from cmath
  • float pow(float base, float exponent)
• Eventually we will write our own functions.
• /usr/include/math.h has additional constants.
  • We will need M_E for the next problem.
• An approximation for n! is $e^{-n}n^n\sqrt{2\pi n}$.
  • Compute 15! directly and using this approximation.
  • This is problem 3 from page 134