CSCI-1200 Computer Science II — Spring 2006
Lecture 9 — Introduction to Recursion
Review from Lecture 8
•Returning const references to member variables provides access to important variables without the cost of
copying and without the danger of allowing them to be changed.
•Lists vs. vectors
•Iterators
•Special properties of vector iterators
•The erase function from vectors and lists.
•Sieve of Eratosthenes
Today’s Lecture
•Introduction to recursion: factorials and exponentiation
•How recursion works
•Iteration vs. recursion
•Rules for writing recursive functions
•Examples that we will work on together:
–Printing a vector in reverse order
–Binary search
We will look at more sophisticated problems in Lecture 10.
9.1 Recursive Definitions of Factorial and Integer Exponentiation
•The factorial is defined for non-negative integers as
n! = (n·(n−1)! n > 0
1n== 0
•Computing integer powers is defined as:
np=(n·np−1p > 0
1p== 0
9.2 Recursive C++ Functions
C++, like other modern programming languages, allows functions to call themselves. This gives a direct method of
implementing recursive functions.
•Here’s the implementation of factorial:
int fact(int n) {
if (n == 0) {
return 1;
} else {
int result = fact(n-1);
return n * result;
}
}
