Week 11: Recursion / Command Line Parameters / UNIX

Question 1

What is recursion?

Answer 1

Defining something in terms of itself

Question 2

Recursive definitions MUST include

Answer 2

A base case

Question 3

In recursion, the base case is also known as the

Answer 3

Simplest case

Question 4

In recursion, the recursive part is also known as the

Answer 4

General case

Question 5

Why is a base case needed in recursion?

Answer 5

Recursive definitions without a base case will run infinitely

Question 6

Recursion can be an alternative to

Answer 6

Iteration

Question 7

A function that makes use of recursion is called

Answer 7

A recursive method

Question 8

What does a recursive method for defining a factorial look like?

Answer 8

The base case is that the number being tested is 1

Question 9

With recursion, what happens with the memory?

Answer 9

Every time the recursive function calls itself, it creates a new place in memory in the stack frame for the new function call

Question 10

For a RECURSIVE function that calculates the factorial of a number, what is the BASE case?

Answer 10

if (numb == 1) {

result == 1;

}

Question 11

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()*

Answer 11

else {

result = (numb + SumRec( numb - 1));

}

This executes when numb is not equal to 1

Question 12

For a recursive function , how many copies of the code are there?

Answer 12

Just one, like any other function

Question 13

When does the recursive function stop calling itself?

Answer 13

When the base case is reached

Question 14

What happens when the base case is finally reached?

Answer 14

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.

Question 15

The most important function of C is ____ function. It is mostly defined with a return type of _____ and without _____

Answer 15

The most important function of C is main() function. It is mostly defined with a return type of int and without parameters

Question 16

For C, command-line arguments are given after the …

Answer 16

Name of the program in the command-line shell of the operating system

Question 17

To allow a C program to take in command line arguments, we must make the _____ of the _____ have the following two ______

________

and

________

Answer 17

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[])

Question 18

What does a main function is C look like that is designed to take in command-line arguments?

Answer 18

int main( int argc, char *argv[])

Question 19

In a C main function parameter that is intended to take command-line arguments, the first parameter ____ should….

Answer 19

int argc

Should never be negative

Question 20

In C, for a command-line argument main function, the command line argument argv[0] is what?

Answer 20

The name of the program

Question 21

In C, for a command-line argument main function, argc stands for what?

Answer 21

ARGument Count

Question 22

In C, for a command-line argument main function, argv means what?

Answer 22

ARGument Vector

Question 23

What are the properties of command-line arguments?

Answer 23

1. They are passed to main() function.
2. They are parameters/arguments supplied to the program when it is invoked.
3. They are used to control program from outside instead of hard coding those values inside the code.
4. argv[argc] is a NULL pointer.
5. argv[0] holds the name of the program.
6. argv[1] points to the first command line argument and argv[n] points last argument.

Question 24

To pass multiple words as a single command-line argument, you can…

Answer 24

Surround them with double or single quotes

Question 25

What must be included in order to use functions such as getting a process ID?

Answer 25

include

Question 26

What data type is a process ID?

Answer 26

pid_t

Question 27

To get a process ID what must be done first?

Answer 27

include

pid_t n = getpid()

Question 28

What lines are required to get the current working directory?

Answer 28

include unistd.h

char *getcwd(char *buf, size_t size);

int chdir(const char *path);

Question 29

The time.h header includes _ different representations of time

___

___

Answer 29

Two different representations of time:

time_t

struct tm

Question 30

struct tm

Has what information?

Answer 30

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

}

Question 31

struct tm tm_wday has information regarding the ____

if tm_wday = 0 what does this mean?

6?

3?

Answer 31

struct tm tm_wday has information regarding the day of the week

if tm_wday = 0 the day is SUNDAY

6 = SATURDAY

3 = WEDNESDAY

Question 32

What is the difference between tm_mday and tm_wday

Answer 32

tm_mday is the day of the month while tm_wday is the day of the week from 0-6

Question 33

In a C program we can run a UNIX command using …

Answer 33

The system() function

form: int k = system(“string”);

Question 34

In a C program we can pipe using the…

Answer 34

popen() function

popen(“command”, “mode”);

if mode is r, for read

if mode is w, for write

Question 35

In a C program, to run a command or program IN PLACE of the current program, use….

Answer 35

execl()

Question 36

execl() does what and has what parameters?

Answer 36

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).

Question 37

To run several processes im parallel, use the ___ function

Answer 37

fork() function

Question 38

fork() returns … if a child process and … if the parent process, otherwise …

Answer 38

fork() returns 0 if a child process and the child process ID if the parent process, otherwise -1 if there was an error