1. Functions and Recursion
By Hector M Lugo-Cordero
September 10, 2008
Department of Electrical and Computer Engineering

2. The Department of Electrical and Computer Engineering
Outline
Functions
Parameters
Return Value
Recursion
Base Case
Process Stack
The Department of Electrical and Computer Engineering

3. The Department of Electrical and Computer Engineering
Functions
Functions
A function is a piece of code that performs specific tasks
Allows code reuse
Syntax
<return_type> <name_of_function>(<params>){
//code goes here
[return statement] }
Functions can be declared before or after main
The Department of Electrical and Computer Engineering

4. The Department of Electrical and Computer Engineering
Recursion
Recursion
Recursion is the act of a function calling itself
The computer can easily run out of memory
Thus the base case is then introduced
Indicates when the function will stop calling itself
Each function run has a different process stack
The Department of Electrical and Computer Engineering

5. The Department of Electrical and Computer Engineering
Examples
Write a function that simulates Windows system(“pause”) command for a Linux computer.
void pause(){ … }
Write a function that compares two integers
int compare(int x, int y){ … }
This funcion returns
1 if x is greater than y
0 if x is equal to y
-1 if x is less than y
The Department of Electrical and Computer Engineering

6. The Department of Electrical and Computer Engineering
Examples (cont.)
Write a function that checks if a number is prime or not
bool isPrime(int num){ … }
The function checks if num is 2 if so returns true
If not then it verifies if the number is even in which case returns false if it is
Finally if none of these conditions are met then it starts dividing num by 3, 5, 7, … until it finds that any of these divides the number, in which case returns false
The function returns true if the divisor is greater than the square root of the number
The Department of Electrical and Computer Engineering

7. The Department of Electrical and Computer Engineering
Questions? ?
The Department of Electrical and Computer Engineering