Week 11: Recursion / Command Line Parameters / UNIX Flashcards
What is recursion?
Defining something in terms of itself
Recursive definitions MUST include
A base case
In recursion, the base case is also known as the
Simplest case
In recursion, the recursive part is also known as the
General case
Why is a base case needed in recursion?
Recursive definitions without a base case will run infinitely
Recursion can be an alternative to
Iteration
A function that makes use of recursion is called
A recursive method
What does a recursive method for defining a factorial look like?
The base case is that the number being tested is 1
With recursion, what happens with the memory?
Every time the recursive function calls itself, it creates a new place in memory in the stack frame for the new function call
For a RECURSIVE function that calculates the factorial of a number, what is the BASE case?
if (numb == 1) {
result == 1;
}
For a RECURSIVE function that calculates the factorial of a number, what is the NON BASE case? When does it execute?
*given the function is called SumRec()*
else {
result = (numb + SumRec( numb - 1));
}
This executes when numb is not equal to 1
For a recursive function , how many copies of the code are there?
Just one, like any other function
When does the recursive function stop calling itself?
When the base case is reached
What happens when the base case is finally reached?
One after one, the function returns by popping off the runtime stack to the calling function until we get to the first call of the function.
The most important function of C is ____ function. It is mostly defined with a return type of _____ and without _____
The most important function of C is main() function. It is mostly defined with a return type of int and without parameters
For C, command-line arguments are given after the …
Name of the program in the command-line shell of the operating system
To allow a C program to take in command line arguments, we must make the _____ of the _____ have the following two ______
________
and
________
To allow a C program to take in command line arguments, we must make the main function of the file have the following two parameters
first argument is the number of command-line arguments
and
the second is the list of the arguments
int main( int argc, char *argv[])
What does a main function is C look like that is designed to take in command-line arguments?
int main( int argc, char *argv[])
In a C main function parameter that is intended to take command-line arguments, the first parameter ____ should….
int argc
Should never be negative
In C, for a command-line argument main function, the command line argument argv[0] is what?
The name of the program
In C, for a command-line argument main function, argc stands for what?
ARGument Count
In C, for a command-line argument main function, argv means what?
ARGument Vector
What are the properties of command-line arguments?
- They are passed to main() function.
- They are parameters/arguments supplied to the program when it is invoked.
- They are used to control program from outside instead of hard coding those values inside the code.
- argv[argc] is a NULL pointer.
- argv[0] holds the name of the program.
- argv[1] points to the first command line argument and argv[n] points last argument.
To pass multiple words as a single command-line argument, you can…
Surround them with double or single quotes
What must be included in order to use functions such as getting a process ID?
include
What data type is a process ID?
pid_t
To get a process ID what must be done first?
include
pid_t n = getpid()
What lines are required to get the current working directory?
include unistd.h
char *getcwd(char *buf, size_t size);
int chdir(const char *path);
The time.h header includes _ different representations of time
___
___
Two different representations of time:
time_t
struct tm
struct tm
Has what information?
struct tm{
int tm_sec; // seconds [0,61]
int tm_min; // minutes [0,59]
int tm_hour; // hour [0,23]
int tm_mday; // day of month [1,31]
int tm_mon; // month of year [0,11]
int tm_year; // years since 1900
int tm_wday; // day of week [0,6] (Sunday = 0)
int tm_yday; // day of year [0,365]
int tm_isdst; // daylight savings flag
}
struct tm tm_wday has information regarding the ____
if tm_wday = 0 what does this mean?
6?
3?
struct tm tm_wday has information regarding the day of the week
if tm_wday = 0 the day is SUNDAY
6 = SATURDAY
3 = WEDNESDAY
What is the difference between tm_mday and tm_wday
tm_mday is the day of the month while tm_wday is the day of the week from 0-6
In a C program we can run a UNIX command using …
The system() function
form: int k = system(“string”);
In a C program we can pipe using the…
popen() function
popen(“command”, “mode”);
if mode is r, for read
if mode is w, for write
In a C program, to run a command or program IN PLACE of the current program, use….
execl()
execl() does what and has what parameters?
Transfers the current process to the one called, it has the following parameters:
int execl(const char *path, const char *arg0, …, const char *argn, char * /*NULL*/);
path is the pathname of the executable file. arg0 should be the same as path or the filename. arg1 to argn are the actual arguments The last parameter must be NULL (or 0).
To run several processes im parallel, use the ___ function
fork() function
fork() returns … if a child process and … if the parent process, otherwise …
fork() returns 0 if a child process and the child process ID if the parent process, otherwise -1 if there was an error
