1. CSC 107 – Programming For Science

2. Today’s Goal  Discuss writing functions that return values  return statement’s meaning and how it works  When and why we use the return statement  Why skipping return statements are bad ideas

3. Why We Use Functions  Simplify code  Replace copies of code by placing in single location  Locate commonly-used computations & actions  Good to find code, but can only return a single value  Input & output performed in these functions  Will discuss ways to change parameters’ values

4. Functions  Already been programming with functions  Built-in functions like pow, exp, & log  Writing & using programmer-defined function: main  All functions similar  Will be using same process to call function  Handling return result same for all functions  Process is same for variables, scoping, passing data

5. Functions  All functions similar, differ only in who wrote it Built-in Function WriterUser-Defined Function Writer

6. Function Names  Rules over legal names identical to variables  Letter or underscore start name for it to be legal  Can use any letters, numbers, or underscore after  Names should be unique (including variables)  Function names rely upon relaxed style rules  Start with a letter & make name meaningful  Names should only use words you would say to:

7. Function Declaration

8. Return Type  Functions must specify their return type  Type of value returned by the function float abs(float x); double pow(double x, double t); int main();  Use special return type, void, if no value is returned void goodSoldier(); void doSomethingWithX(int x);

9. Function Definitions

10. return Statement

11. return Examples

17. return Statement

18. return Examples

19. Multiple return Statements  Multiple return s possible in a single function  Each time function is called, only one is executed  Gives greater flexibility by not tying code down bool userTypedOddNumber() { int num; cout > num; if ( (num % 2) == 1) { return true; } else { return false; } }

20. Your Turn  Get into your groups and try this assignment

21. For Next Lecture  Read about parameters in Section 9.4 – 9.4.3  How do we pass values to a function?  How does a function take in those values?  What can a function do to those values?  Weekly Assignment #6 out & due next Tues.  Avoid the rush by start working on it now  Programming Assignment #2 now on Angel  This is a larger assignment and due in 3 weeks