CS Week 2 - Streams

Question 1

ostream

Answer 1

output stream
a class that supports output
available via iostream and in namespace std

Question 2

insertion operator

Answer 2

&laquo_space;
for converting different types of data into a sequence of characters, that sequence is normally placed into a buffer, and the system then outputs the buffer at various times

Question 3

cout

Answer 3

a predefined ostream object that is pre-associated with a system’s standard output, usually a computer screen

Question 4

how the ostream &laquo_space;works

Answer 4

1. the insertion operator converts the string literal to characters, temporarily storing characters in an output buffer
2. the system then writes the buffer’s content to the screen

Question 5

istream

Answer 5

input stream
a class that supports input
available via iostream

Question 6

extraction operator

Answer 6

> > to extract data from a buffer and write the data into different types of variables

Question 6

cin

Answer 6

a predefined istream pre-associated with a system’s standard input, usually a keyboard

Question 6

how istream&raquo_space; works

Answer 6

1. the system automatically puts the standard input into a data buffer associated with cin
2. > > operator skips leading whitespace and extacts as many characters as possible consistent with the target variable’s type
3. the operator then stops at the next whitespace
4. converts the extracted characters to the target variable’s type and stores the result into the variable

Question 6

to read file input

Answer 6

include <fstream></fstream>

can create a new input stream that comes from a file

ifstream inFS;

inFS.open(str);

if(!inFS.is_open()){
cout &laquo_space;“error opening”; return 1;}

inFS&raquo_space; aVar;

inFS.close();

Question 7

when would we use cin, cout, ifstream, ofstream, istringstream, ostringstream

Answer 7

cin - input from the keyboard

cout - output to the screen

ifstream - input from a file

ofstream - write to a file

istringstream - read input from a string

ostringstream - insert characters into a string buffer (instead of screen)

Question 8

reading to the end of the file

Answer 8

while (inFS&raquo_space; aVar) {
//do something with aVar;
}

Question 9

inFS.eof();

Answer 9

returns true if the previous stream operation reached the end of the file

Question 10

inFS.fail();

Answer 10

returns true if the previous stream operation had an error
- instead of this use while (inFS&raquo_space; aVar){ /do something/ }

Question 11

stream error

Answer 11

occurs when insertion or extraction fails causing the stream to enter an error state
- wrong type, too large, too small
- may skips extraction, set the var to 0, or set the var to the max or min of the type

Question 12

inFS.clear();
inFS.good();
inFS.eof();
inFS.fail();
inFS.bad();

and when to use

Answer 12

1-bit error flags

clear - stream’s error state is cleared

good- returns true if no stream errors have occurred

eof - returns value of eofbit, if end of file reached on extraction

fail - returns true if either failbit or badbit is set, indicating an error for the previous stream operation

bad - returns true id badbit is set. indicating the stream is bad

• use if you want to know what went wrong

Question 13

how to write to a file

Answer 13

include <fstream></fstream>

declare a variable of type ofstream to write to a file

ofstream outFS;

outFS.open(fileName);

if(!outFS.is_open()) {
//output error
}

outFS &laquo_space;“Hiya!! &laquo_space;endl;

outFS.close();

Question 14

how to ask if the right value was extracted

Answer 14

if (!cin) {
cout &laquo_space;“bad input” &laquo_space;endl;
}

Question 15

how to use input string stream

Answer 15

include <sstream></sstream>

read input from an associated string

istringstream inSS (strToUse);

string firstName;
string lastName;

inSS&raquo_space; firstName;
inSS&raquo_space; lastName;

istringstream inSS;
string lineStr;
string data;
cout &laquo_space;“Enter names separated by spaces” &laquo_space;endl;
getline(cin, lineStr);
inSS.str(lineStr);
while (inSS&raquo_space; data) {
cout &laquo_space;data &laquo_space;endl;
}

Question 16

.get();
» or «

Answer 16

get - gets one character

> > or &laquo_space;- stops at whitespace

getline(stream, storingVar, stopWhere)
stopWhere - “,” or empty to stop at a new line

Question 17

getline with string streams

Answer 17

while (getline(cin, lineStr) {
inSS.str(lineStr);
inSS&raquo_space; name;
}

Question 18

inSS.str();
oSS.str();

Answer 18

.in - copies a string into the string streams input buffer

o- returns the contents of an ostringstream buffer as a string

Question 19

how to use output string stram

Answer 19

include <sstream></sstream>

ostringstream infoOSS;
cin&raquo_space; aVar;

infoOSS &laquo_space;aVar;

string infoStr = infoOSS.str();

Question 20

command line arguments

Answer 20

values entered by a user when running a program from a command line

Question 21

argc

Answer 21

number of command line arguments in argv
- includes the program name itself

int argc

Question 22

argv

Answer 22

array of strings, one string for each command line argument
argv[0] is the program name

char* argv[]

Question 23

when you run the program with argc and argv what happens

Answer 23

• system passes an int parameter argc to main(), indicating the number of command line arguments
• system passes a second parameter argv to main(), defined as an array of string, one string for each command line agument

Question 24

what happens when user does not type in the amount of command lines

Answer 24

extra is ignored
too few cause a problem

• error- accessing elements in argv without first checking argc to ensure the user entered enough arguments, out of range array access

Question 25

usage message

Answer 25

lists a programs expected command line arguments, program should then return 1, indicating the system that an error occurred

if (argc != the size of argv/a #) {
cout &laquo_space;“Usage: programName input 1…input n” &laquo_space;endl;
return 1;
}

Question 26

command line arguments are what…

Answer 26

c strings

Question 27

what converts a string into an integer

Answer 27

in var = atoi(ageStr.c_str());

included in cstdlib

Question 28

putting quotes arounf an arument in a command line…and how should you access argv elements

Answer 28

allows the string to have any number of spaces

[], no .at

Question 29

what do command line arguments and files allow you to do

Answer 29

allow user to specify the location of an input or outpur file

argv[#] - # is where that file is located in the command line

inFS.open(argv[1]);

Question 30

selection sort defifniton

Answer 30

sorting algorithm that treats the input as 2 parts, a sorted part, and an unsorted part and repeatedly selects the proper next value to move from the unsorted to sorted part

Question 31

selection sort code

Answer 31

function to find location of smallest

int locationOfSmallest (const vector<int> v, int begin, int end) {
int smallest = v.at(begin);
int location = being;</int>

for (i = begin + 1; i < end; ++i) {
if (v.at(i) < smallest) {
location =i; }
}
return location;
}
—————–
code in main

for ( i = 0; i < v.size(); ++i) {
location = locationOfSmallest(v, i, v.size());
swap(v.at(i), v.at(location);
}

Question 32

runtime of selection sort algorithm

Answer 32

O(N^2)

a list with N elements
outer loop executes N-1 times
inner loop executes an average of N/2 times

if input increases in size by x times, the runtime increases x^2 times

Question 33

you can use inFS&raquo_space; data in the while conditional when

Answer 33

you know your data is clean

Question 34

both ways of writing argv

Answer 34

char** argv

char* argv[]