I've tried a bunch of methods listed on here but none of them work. It's always waiting for more input.
I've tried while(std::getline(std::cin, line)) and the method below, nothing seems to work:
#include <iostream>
#include <sstream>
using namespace std;
int main(){
long length = 1UL<<32;
int array[length];
// memset(array, 0, (length-1) * sizeof(int));
for(int i = 0; i < length; i++)
array[i] = 0;
string line;
int num;
while(!cin.eof()){
getline(cin,line);
stringstream ss(line);
ss >>num;
array[num]++;
}
for(int i = 0; i < length; i++)
if(array[i]){
cout << i << ": ";
cout << array[i] << endl;
}
}
First off, do not use std::cin.eof() to control your loop! It doesn't work. Also, you always need to check for successful input after the input.
That said, to terminate the input you'll need to enter the appropriate end of file character, probably at the start of the line (how it works entirely somewhat depends on the system, some settings, etc.). On Windows you'd use Ctrl-Z, on UNIXes you'd use Ctrl-D.
First off, this part of your program attempts to allocate 4 GB of memory on the stack, which doesn't work on my machine (good luck finding any machine with 4 GB of continuous memory space):
long length = 1UL<<32;
int array[length];
If I change that to a much more reasonable:
long length = 32;
Then it works fine for me:
$ g++ -g test.cpp -o test && ./test
2
5
# pressed control+d
2: 1
5: 2
$
So I'm guessing something else is wrong.
Note: Unless you actually plan to use all of those indexes, you may want to considering using an unordered_map, so you only use the space you actually need.
The condition you are looking for can be most easily tested by evaluating "std::cin" as a bool, i.e. while (cin). But it won't do this until you have tried to read beyond EOF, so expect an empty getline:
#include <iostream>
#include <string>
int main() {
std::string input;
while (std::cin) {
std::cout << "Type something in:\n";
std::getline(std::cin, input);
if(input.empty())
continue;
std::cout << "You typed [" << input << "]\n";
}
std::cout << "Our work here is done.\n";
return 0;
}
Live demo: http://ideone.com/QR9fpM
Related
I'm just beginning to learn C++ and I am having some trouble with a program. It's supposed to sort numbers from an external file. I've managed to successfully code the sorting algorithm, but I am having trouble working with the external file. I am just testing some things out in a separate program to gain an understanding of how things like ifstream work. I should be able to figure out how to implement it into my program once I gain a better understanding of how it works.
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
int main() {
using namespace std;
int count;
ifstream InFile;
InFile.open ("unsorted.txt");
InFile >> count;
int numbers[count];
for(int a = 0; a < count; a++)
InFile >> numbers[a];
cout << numbers << endl;
}
Currently, the output for this is 0x7ffc246c98e0 I am not sure why this is the case I'm just attempting to print my file of integers. Could anyone help explain what I am doing wrong? I'd be very thankful.
When you do
cout << numbers << endl;
you print the pointer to the first element of the array.
You want
cout << numbers[a] << '\n';
to print the current element.
Furthermore, if that's all your program is doing, then you don't actually need the array. All you need is a single int variable:
int value;
for (int a = 0; a < count; ++a)
{
InFile >> value;
cout << value << '\n';
}
That also solve the problem with the variable-length array (since there isn't any).
If you intend to use count variable to count the file size or something, it is where your code goes wrong. You can't count the length of the file as like as you are trying.
while( getline ( InFile, line ) )
{
count += line.length();
}
Maybe, try like this!!!
If you use
InFile>>count;
it would try to store all the string from InFile stream to count, which is not intended.
I'm having difficulties with a particular piece of code I'm learning from "Programming Principles And Practice Using C++".
I can't get an output from a loop refering to a vector. Am using std_lib_facilities and stdafx because the book and MVS told me so.
#include "stdafx.h"
#include "../../std_lib_facilities.h"
int main()
{
vector<string>words;
for(string temp; cin>>temp; )
words.push_back(temp);
cout << "Number of words: " << words.size() << '\n';
}
This will produce nothing. I'll get the prompt, type in some words, then enter, then nothing.
Tried some variations I got here and from other websites as well, such as:
//here i tried the libraries the guy used in his code
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
cout << "Please enter a series of words followed by End-of-File: ";
vector<string> words;
string word;
string disliked = "Broccoli";
while (cin >> word)
words.push_back(word);
cout << "\nNumber of words: " << words.size() << endl;
// cycle through all strings in vector
for (int i = 0; i < words.size(); ++i)
{
if (words[i] != disliked)
cout << words[i] << endl;
else
cout << "BLEEP!\n";
}
return 0;
}
Still nothing.
After trying some things, by elimination I'm pretty certain the problem is with the loop-to-vector communication, because all of these work fine:
int main()
{
vector<string>words = { "hi" };
words.push_back("hello");
cout << words[1] << "\n"; // this will print hello
for (int i = 0; i < words.size();++i) {
cout << words[i] << "\n"; // this will print out all elements
// inside vector words, ( hi, hello)
}
cout << words.size();// this will print out number 2
for (string temp; cin >> temp;) {
words.push_back(temp);
}
cout << words.size();// this won't do anything after i type in some
// words; shouldn't it increase the size of the
// vector?
}
Neither will this alone:
int main()
{
vector<string>words = { "hi" };
for (string temp; cin >> temp;) {
words.push_back(temp);
}
cout << words.size();
}
What am I missing, please? Thank you in advance.
Input the strings and when done press Ctrl+Z (followed by Enter) if on Windows or Ctrl+D if on Linux. When you do that the cin>>temp; condition inside your for loop will evaluate to false and your program will exit the loop.
Firstly, it is not necessary to use the std_lib_facilities.h. That is just something used in the book to avoid having every example in the book regularly include a set of standard headers, or to correct for non-standard behaviours between compilers. It is also a header that that does using namespace std - you will find numerous examples (both on SO and the wider internet) explaining why it is VERY poor practice to have using namespace std in a header file.
Second, it is not necessary to use stdafx.h either. That is something generated by Microsoft IDE, and provides a means of speeding up compilation in large projects, because of how it causes the compiler to work with precompiled headers. If you only expect to use Microsoft compilers, then feel free to fill your boots and use this one. However, it is not standard C++, may (depending on IDE and project settings) include windows specific headers that will not work with non-Microsoft compilers, and in forums will probably discourage people who use other compilers from helping you - since they will have good reason to assume your code uses Microsoft-specific extensions, which will mean they probably can't help you.
The first sample of code can be rewritten, in standard C++ (without use of either header above) as
#include <vector> // for std::vector
#include <string> // for std::string
#include <iostream> // std::cout and other I/O facilities
int main()
{
std::vector<std::string> words;
for(std::string temp; std::cin >> temp; )
words.push_back(temp);
std::cout << "Number of words: " << words.size() << '\n';
}
Before you get excited, this will exhibit the same problem (not apparently finishing). The reason is actually the termination condition of the loop - std::cin >> temp will only terminate the loop if end of file or some other error is encountered in the stream.
So, if you type
The cow jumped over the moon
std::cin will continue to wait for input. It is generally necessary for the USER to trigger and end of file condition. Under windows, this requires the user to enter CTRL-Z on an empty line followed by the enter key.
An alternative would be to have some pre-agreed text that cause the loop to exit, such as
#include <vector> // for std::vector
#include <string> // for std::string
#include <iostream> // std::cout and other I/O facilities
int main()
{
std::vector<std::string> words;
for(std::string temp; std::cin >> temp && temp != "zzz"; )
words.push_back(temp);
std::cout << "Number of words: " << words.size() << '\n';
}
which will cause the program to exit when the input contains the word zzz. For example
The cow jumped over the moon zzz
There are other techniques, such as reading one character at a time, and stopping when the user enters two consecutive newlines. That requires your code to interpret every character, and decide what constitutes a word. I'll leave that as an exercise.
Note there is no means in standard C++ to directly read keystrokes - the problems above are related to how standard streams work, and interact with the host system.
The user can also use the program "as is" by placing the same text into an actual file, and (when the program is run) redirect input for your program to come from that file. For example your_executable < filename.
I wrote the code below that successfully gets a random line from a file; however, I need to be able to modify one of the lines, so I need to be able to get the line character by character.
How can I change my code to do this?
Use std::istream::get instead of std::getline. Just read your string character by character until you reach \n, EOF or other errors. I also recommend you read the full std::istream reference.
Good luck with your homework!
UPDATE:
OK, I don't think an example will hurt. Here is how I'd do it if I were you:
#include <string>
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
static std::string
answer (const string & question)
{
std::string answer;
const string filename = "answerfile.txt";
ifstream file (filename.c_str ());
if (!file)
{
cerr << "Can't open '" << filename << "' file.\n";
exit (1);
}
for (int i = 0, r = rand () % 5; i <= r; ++i)
{
answer.clear ();
char c;
while (file.get (c).good () && c != '\n')
{
if (c == 'i') c = 'I'; // Replace character? :)
answer.append (1, c);
}
}
return answer;
}
int
main ()
{
srand (time (NULL));
string question;
cout << "Please enter a question: " << flush;
cin >> question;
cout << answer (question) << endl;
}
... the only thing is that I have no idea why do you need to read string char by char in order to modify it. You can modify std::string object, which is even easier. Let's say you want to replace "I think" with "what if"? You might be better off reading more about
std::string and using find, erase, replace etc.
UPDATE 2:
What happens with your latest code is simply this - you open a file, then you get its content character by character until you reach newline (\n). So in either case you will end up reading the first line and then your do-while loop will terminate. If you look into my example, I did while loop that reads line until \n inside a for loop. So that is basically what you should do - repeat your do-while loop for as many times as many lines you want/can get from that file. For example, something like this will read you two lines:
for (int i = 1; i <= 2; ++i)
{
do
{
answerfile.get (answer);
cout << answer << " (from line " << i << ")\n";
}
while (answer != '\n');
}
I'm trying to count the number of times each letter appears in a file. When I run the code below it counts "Z" twice. Can anyone explain why?
The test data is:
abcdefghijklmnopqrstuvwxyz
ABCDEFGHIJKLMNOPQRSTUVWXYZ
#include <iostream> //Required if your program does any I/O
#include <iomanip> //Required for output formatting
#include <fstream> //Required for file I/O
#include <string> //Required if your program uses C++ strings
#include <cmath> //Required for complex math functions
#include <cctype> //Required for letter case conversion
using namespace std; //Required for ANSI C++ 1998 standard.
int main ()
{
string reply;
string inputFileName;
ifstream inputFile;
char character;
int letterCount[127] = {};
cout << "Input file name: ";
getline(cin, inputFileName);
// Open the input file.
inputFile.open(inputFileName.c_str()); // Need .c_str() to convert a C++ string to a C-style string
// Check the file opened successfully.
if ( ! inputFile.is_open())
{
cout << "Unable to open input file." << endl;
cout << "Press enter to continue...";
getline(cin, reply);
exit(1);
}
while ( inputFile.peek() != EOF )
{
inputFile >> character;
//toupper(character);
letterCount[static_cast<int>(character)]++;
}
for (int iteration = 0; iteration <= 127; iteration++)
{
if ( letterCount[iteration] > 0 )
{
cout << static_cast<char>(iteration) << " " << letterCount[iteration] << endl;
}
}
system("pause");
exit(0);
}
As others have pointed out, you have two Qs in the input. The reason you have two Zs is that the last
inputFile >> character;
(probably when there's just a newline character left in the stream, hence not EOF) fails to convert anything, leaving a 'Z' in the global 'character' from the previous iteration. Try inspecting inputFile.fail() afterwards to see this:
while (inputFile.peek() != EOF)
{
inputFile >> character;
if (!inputFile.fail())
{
letterCount[static_cast<int>(character)]++;
}
}
The idiomatic way to write the loop, and which also fixes your 'Z' problem, is:
while (inputFile >> character)
{
letterCount[static_cast<int>(character)]++;
}
There are two Q's in your uppercase string. I believe the reason you get two counts for Z is that you should check for EOF after reading the character, not before, but I am not sure about that.
Well, others already have pointed out the error in your code.
But here is one elegant way you can read the file and count the letters in it:
struct letter_only: std::ctype<char>
{
letter_only(): std::ctype<char>(get_table()) {}
static std::ctype_base::mask const* get_table()
{
static std::vector<std::ctype_base::mask>
rc(std::ctype<char>::table_size,std::ctype_base::space);
std::fill(&rc['A'], &rc['z'+1], std::ctype_base::alpha);
return &rc[0];
}
};
struct Counter
{
std::map<char, int> letterCount;
void operator()(char item)
{
if ( item != std::ctype_base::space)
++letterCount[tolower(item)]; //remove tolower if you want case-sensitive solution!
}
operator std::map<char, int>() { return letterCount ; }
};
int main()
{
ifstream input;
input.imbue(std::locale(std::locale(), new letter_only())); //enable reading only leters only!
input.open("filename.txt");
istream_iterator<char> start(input);
istream_iterator<char> end;
std::map<char, int> letterCount = std::for_each(start, end, Counter());
for (std::map<char, int>::iterator it = letterCount.begin(); it != letterCount.end(); ++it)
{
cout << it->first <<" : "<< it->second << endl;
}
}
This is modified (untested) version of this solution:
Elegant ways to count the frequency of words in a file
For one thing, you do have two Q's in the input.
Regarding Z, #Jeremiah is probably right in that it is doubly counted due to it being the last character, and your code not detecting EOF properly. This can be easily verified by e.g. changing the order of input characters.
As a side note, here
for (int iteration = 0; iteration <= 127; iteration++)
your index goes out of bounds; either the loop condition should be iteration < 127, or your array declared as int letterCount[128].
Given that you apparently only want to count English letters, it seems like you should be able to simplify your code considerably:
int main(int argc, char **argv) {
std::ifstream infile(argv[1]);
char ch;
static int counts[26];
while (infile >> ch)
if (isalpha(ch))
++counts[tolower(ch)-'a'];
for (int i=0; i<26; i++)
std::cout << 'A' + i << ": " << counts[i] <<"\n";
return 0;
}
Of course, there are quite a few more possibilities. Compared to #Nawaz's code (for example), this is obviously quite a bit shorter and simpler -- but it's also more limited (e.g., as it stands, it only works with un-accented English characters). It's pretty much restricted to the basic ASCII letters -- EBCDIC encoding, ISO 8859-x, or Unicode will break it completely.
His also makes it easy to apply the "letters only" filtration to any file. Choosing between them depends on whether you want/need/can use that flexibility or not. If you only care about the letters mentioned in the question, and only on typical machines that use some superset of ASCII, this code will handle the job more easily -- but if you need more than that, it's not suitable at all.
I'm obviously not quite getting the 'end-of-file' concept with C++ as the below program just isn't getting past the "while (cin >> x)" step. Whenever I run it from the command line it just sits there mocking me.
Searching through SO and other places gives a lot of mention to hitting ctrl-z then hitting enter to put through an end-of-file character on windows, but that doesn't seem to be working for me. That makes me assume my problem is elsewhere. Maybe defining x as a string is my mistake? Any suggestions about where I'm going wrong here would be great.
Note: sorry for the lack of comments in the code - the program itself is supposed to take in a series of
words and then spit back out the count for each word.
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>
using std::cin;
using std::cout; using std::endl;
using std::sort;
using std::string; using std::vector;
int main()
{
cout << "Enter a series of words separated by spaces, "
"followed by end-of-file: ";
vector<string> wordList;
string x;
while (cin >> x)
wordList.push_back(x);
typedef vector<string>::size_type vec_sz;
vec_sz size = wordList.size();
if (size == 0) {
cout << endl << "This list appears empty. "
"Please try again." << endl;
return 1;
}
sort(wordList.begin(), wordList.end());
cout << "Your word count is as follows:" << endl;
int wordCount = 1;
for (int i = 0; i != size; i++) {
if (wordList[i] == wordList[i+1]) {
wordCount++;
}
else {
cout << wordList[i] << " " << wordCount << endl;
wordCount = 1;
}
}
return 0;
}
If you're on windows ^Z has to come as the first character after a newline, if you're on a unixy shell then you want to type ^D.
The input portion of your code works. The only real problem I see is with the loop the tries to count up the words:
for (int i = 0; i != size; i++) {
if (wordList[i] == wordList[i+1]) {
The valid subscripts for wordList run from 0 through size-1. In the last iteration of your loop, i=size-1, but then you try to use wordList[i+1], indexing beyond the end of the vector and getting undefined results. If you used wordList.at(i+1) instead, it would throw an exception, quickly telling you more about the problem.
My guess is that what's happening is that you're hitting Control-Z, and it's exiting the input loop, but crashing when it tries to count the words, so when you fix that things will work better in general. If you really can't get past the input loop after fixing the other problem(s?), and you're running under Windows, you might try using F6 instead of entering control-Z -- it seems to be a bit more dependable.
I pretty much always use getline when using cin (particularly when what I want is a string):
istream& std::getline( istream& is, string& s );
So, you'd call getline(cin, x) and it would grab everything up to the newline. You have to wait for the newline for cin to give you anything anyway. So, in that case, your loop would become:
while(getline(cin, x))
wordList.push_back(x);
cin does not accept blank space or line breaks so execution of cin does not complete unless you enter something , here is a test program that gives you what you want
#include "stdafx.h"
#include<iostream>
#include <string>
#include <sstream>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string str = "";
while(std::getline(cin, str) && str!="")
{
cout<<"got "<<str<<endl;
}
cout<<"out"<<endl;
cin>>str;
return 0;
}