I am having a really hard time with this problem...
Write a program that reads two strings (that do not contain blanks)
called searchPattern and longSequence.
The program will display in the screen the positions where
searchPattern appears in longSequence.
For example, when
seachPattern is asd
and longSewuence is asdfasdfasdfasdf
(the positions are 0123456789012345)
the program will display 0, 4, 8, 12.
Another example, when
seachPattern is jj
and longSewuence is kjlkjjlkjjjlkjjjkl
(the positions are 012345678901234567)
the program will display 4, 8, 9, 13, 14.
can anyone help?
Some hints:
Read in the two strings. Look up "std::cin" for how to read and "std::string" for how to store the strings.
Look at the std::string class's find() method to search for the substring in the long string.
Have a go and then post what you have done on here. You will find plenty of people happy to help you, but you have to make some effort yourself. :-)
As a starting point, maybe just write the part that reads in the strings. When that is working well, you can add features.
Good luck.
To start thinking about the solution of problems like this, the best way is to think how you would solve it using a pen and paper in as much detail as possible and then try to translate that to code.
I would use Test Driven Development and start out small and build up.
For example, forget about user I/O, and stick with hard-coded data:
#include <iostream>
#include <string>
using std::cout;
using std::endl;
using std::string;
int main(void) // For now, can be modified later.
{
const char pattern[] = "asd";
const char sequence[] = "asdfasdfasdfasdf";
std::string::size_type position = 0;
const std::string longSequence(sequence);
position = longSequence.find(pattern, position);
while (position != std::string::npos)
{
cout << "pattern found at position: " << position << endl;
position = longSequence.find(pattern, position);
}
cout << "Paused. Press ENTER to continue." << endl;
cin.ignore(100000, '\n');
return 0;
}
You may want to convert the above into using a state machine rather than using std::string::find(). Again, this is just a foundation to build upon.
It's a recursive backtracking problem. Just like getting the mouse out of the maze. Define your base cases and your paths through the data. In the end all you need is a single function of maybe 15 - 20 lines.
Related
Is there a way thorough which I can see what character occupies a certain coordinate. Let's say I have the following output:
Hello World !
I want to able to to see the x character on the y line. Something like:
readCoordinates(0,3);
This function should return 'l' , because the 4th character (because I started counting from 0) from the 1st line is 'l'. Can I do this type of readings in C++ from an already printed string ?
You might consider defining your own custom print function, which logs in a vector everything you've already outputted to the console. That way, you could easily grab a character, or string, from the console.
It might take up a lot of memory, however, if you're outputting thousands of lines.
You could do this from the string that is printed, but after it is printed it is just pixels on a screen, or ink on a printer. So, the answer is no, unless you have e.g. a vision system to look around and see where it was printed, recognize the letters and lines, and figure out the coordinates.
"Can I do this type of readings in C++ from an already printed string ?"
Good approach would be to store output of your program in memory so that your function readCoordinates could access random character in O(1). I would definitely use std::vector<std::string> outputBuffer which would allow you something like this: outputBuffer[0][3].
Example:
#include <iostream>
#include <vector>
#include <string>
std::vector<std::string> outputBuffer;
char readCoordinates(int line, int character)
{
if (line < outputBuffer.size() && character < outputBuffer[line].size())
return outputBuffer[line][character];
return 0;
}
int main()
{
std::string myOutput("Hello World !");
outputBuffer.push_back(myOutput);
std::cout << myOutput << std::endl;
if (char c = readCoordinates(0, 3))
std::cout << c << std::endl;
}
output:
Hello World !
l
i have a text file with data like the following:
name
weight
groupcode
name
weight
groupcode
name
weight
groupcode
now i want write the data of all persons into a output file till the maximum weight of 10000 kg is reached.
currently i have this:
void loadData(){
ifstream readFile( "inFile.txt" );
if( !readFile.is_open() )
{
cout << "Cannot open file" << endl;
}
else
{
cout << "Open file" << endl;
}
char row[30]; // max length of a value
while(readFile.getline (row, 50))
{
cout << row << endl;
// how can i store the data into a list and also calculating the total weight?
}
readFile.close();
}
i work with visual studio 2010 professional!
because i am a c++ beginner there could be is a better way! i am open for any idea's and suggestions
thanks in advance!
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <limits>
struct entry
{
entry()
: weight()
{ }
std::string name;
int weight; // kg
std::string group_code;
};
// content of data.txt
// (without leading space)
//
// John
// 80
// Wrestler
//
// Joe
// 75
// Cowboy
int main()
{
std::ifstream stream("data.txt");
if (stream)
{
std::vector<entry> entries;
const int limit_total_weight = 10000; // kg
int total_weight = 0; // kg
entry current;
while (std::getline(stream, current.name) &&
stream >> current.weight &&
stream.ignore(std::numeric_limits<std::streamsize>::max(), '\n') && // skip the rest of the line containing the weight
std::getline(stream, current.group_code))
{
entries.push_back(current);
total_weight += current.weight;
if (total_weight > limit_total_weight)
{
break;
}
// ignore empty line
stream.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
}
else
{
std::cerr << "could not open the file" << std::endl;
}
}
Edit: Since you wannt to write the entries to a file, just stream out the entries instead of storing them in the vector. And of course you could overload the operator >> and operator << for the entry type.
Well here's a clue. Do you see the mismatch between your code and your problem description? In your problem description you have the data in groups of four lines, name, weight, groupcode, and a blank line. But in your code you only read one line each time round your loop, you should read four lines each time round your loop. So something like this
char name[30];
char weight[30];
char groupcode[30];
char blank[30];
while (readFile.getline (name, 30) &&
readFile.getline (weight, 30) &&
readFile.getline (groupcode, 30) &&
readFile.getline (blank, 30))
{
// now do something with name, weight and groupcode
}
Not perfect by a long way, but hopefully will get you started on the right track. Remember the structure of your code should match the structure of your problem description.
Have two file pointers, try reading input file and keep writing to o/p file. Meanwhile have a counter and keep incrementing with weight. When weight >= 10k, break the loop. By then you will have required data in o/p file.
Use this link for list of I/O APIs:
http://msdn.microsoft.com/en-us/library/aa364232(v=VS.85).aspx
If you want to struggle through things to build a working program on your own, read this. If you'd rather learn by example and study a strong example of C++ input/output, I'd definitely suggest poring over Simon's code.
First things first: You created a row buffer with 30 characters when you wrote, "char row[30];"
In the next line, you should change the readFile.getline(row, 50) call to readFile.getline(row, 30). Otherwise, it will try to read in 50 characters, and if someone has a name longer than 30, the memory past the buffer will become corrupted. So, that's a no-no. ;)
If you want to learn C++, I would strongly suggest that you use the standard library for I/O rather than the Microsoft-specific libraries that rplusg suggested. You're on the right track with ifstream and getline. If you want to learn pure C++, Simon has the right idea in his comment about switching out the character array for an std::string.
Anyway, john gave good advice about structuring your program around the problem description. As he said, you will want to read four lines with every iteration of the loop. When you read the weight line, you will want to find a way to get numerical output from it (if you're sticking with the character array, try http://www.cplusplus.com/reference/clibrary/cstdlib/atoi/, or try http://www.cplusplus.com/reference/clibrary/cstdlib/atof/ for non-whole numbers). Then you can add that to a running weight total. Each iteration, output data to a file as required, and once your weight total >= 10000, that's when you know to break out of the loop.
However, you might not want to use getline inside of your while condition at all: Since you have to use getline four times each loop iteration, you would either have to use something similar to Simon's code or store your results in four separate buffers if you did it that way (otherwise, you won't have time to read the weight and print out the line before the next line is read in!).
Instead, you can also structure the loop to be while(total <= 10000) or something similar. In that case, you can use four sets of if(readFile.getline(row, 30)) inside of the loop, and you'll be able to read in the weight and print things out in between each set. The loop will end automatically after the iteration that pushes the total weight over 10000...but you should also break out of it if you reach the end of the file, or you'll be stuck in a loop for all eternity. :p
Good luck!
Apologies in advance, because I suspect this may be a silly question.
I have written a function for reading in data from an external file. I then use the data to perform calculations using other code I have written.
The function works by finding a data label that looks like this:
const std::string findMe = "<dataLabel>";
Each time I want to find data, I replace dataLabel with the label of whichever data I need from the file.
Here's what I want to do.
I don't want to have to write in the label of the data I want each time. I want to be able to do this:
for (int i = 0; i < anyNumberOfDataSets; i++)
{
findMe = "<dataLabeli>";
// Then run function for reading in data, put data into a vector.
}
I could then add any number of data sets to my external file, give each one the title
, and have each data set read into a vector.
The problem is, I simply can't figure out how to write findMe = "<dataLabeli>". Is this even possible?
I have tried things like, findMe = "<dataLabel" << i <<, but no luck!
Any suggestions would be much appreciated.
It is very hard to understand what you mean, but I guess you want this
#include <sstream>
#include <string>
for (int i = 0; i < anyNumberOfDataSets; i++)
{
std::ostringstream strm;
strm << "<dataLabel" << i << ">";
const std::string findMe = strm.str();
//...
//proceed with searching findMe
}
You can read more about string streams, for instance, here
you've already got the right answer, so this is just trying to help you with solving such problems in the future:
Your core problem here is to convert the integer i into a string s (if you've done this, than you just do findMe = "<datalabel"; findMe += s; findMe += ">";.
Googling for c++ convert integer into string will give you this as the first result. Problem solved.
This is not saying "use google before/instead of asking", it's rather "try to identify the core problem".
Another solution:
using namespace boost;
findMe = str(format("<dataLabel%d>") % i);
This will substitute %d with the value of i, formatted like printf() does.
ifstream toOpen;
openFile.open("sample.html", ios::in);
if(toOpen.is_open()){
while(!toOpen.eof()){
getline(toOpen,line);
if(line.find("href=") && !line.find(".pdf")){
start_pos = line.find("href");
tempString = line.substr(start_pos+1); // i dont want the quote
stop_pos = tempString .find("\"");
string testResult = tempString .substr(start_pos, stop_pos);
cout << testResult << endl;
}
}
toOpen.close();
}
What I am trying to do, is to extrat the "href" value. But I cant get it works.
EDIT:
Thanks to Tony hint, I use this:
if(line.find("href=") != std::string::npos ){
// Process
}
it works!!
I'd advise against trying to parse HTML like this. Unless you know a lot about the source and are quite certain about how it'll be formatted, chances are that anything you do will have problems. HTML is an ugly language with an (almost) self-contradictory specification that (for example) says particular things are not allowed -- but then goes on to tell you how you're required to interpret them anyway.
Worse, almost any character can (at least potentially) be encoded in any of at least three or four different ways, so unless you scan for (and carry out) the right conversions (in the right order) first, you can end up missing legitimate links and/or including "phantom" links.
You might want to look at the answers to this previous question for suggestions about an HTML parser to use.
As a start, you might want to take some shortcuts in the way you write the loop over lines in order to make it clearer. Here is the conventional "read line at a time" loop using C++ iostreams:
#include <fstream>
#include <iostream>
#include <string>
int main ( int, char ** )
{
std::ifstream file("sample.html");
if ( !file.is_open() ) {
std::cerr << "Failed to open file." << std::endl;
return (EXIT_FAILURE);
}
for ( std::string line; (std::getline(file,line)); )
{
// process line.
}
}
As for the inner part the processes the line, there are several problems.
It doesn't compile. I suppose this is what you meant with "I cant get it works". When asking a question, this is the kind of information you might want to provide in order to get good help.
There is confusion between variable names temp and tempString etc.
string::find() returns a large positive integer to indicate invalid positions (the size_type is unsigned), so you will always enter the loop unless a match is found starting at character position 0, in which case you probably do want to enter the loop.
Here is a simple test content for sample.html.
<html>
<a href="foo.pdf"/>
</html>
Sticking the following inside the loop:
if ((line.find("href=") != std::string::npos) &&
(line.find(".pdf" ) != std::string::npos))
{
const std::size_t start_pos = line.find("href");
std::string temp = line.substr(start_pos+6);
const std::size_t stop_pos = temp.find("\"");
std::string result = temp.substr(0, stop_pos);
std::cout << "'" << result << "'" << std::endl;
}
I actually get the output
'foo.pdf'
However, as Jerry pointed out, you might not want to use this in a production environment. If this is a simple homework or exercise on how to use the <string>, <iostream> and <fstream> libraries, then go ahead with such a procedure.
This looks like homework stuff but please be assured that it isn't homework. Just an exercise in the book we use in our c++ course, I'm trying to read ahead on pointers..
The exercise in the book tells me to split a sentence into tokens and then convert each of them into pig latin then display them..
pig latin here is basically like this: ball becomes allboy in piglatin.. boy becomes oybay.. take the first letter out, put it at the end then add "ay"..
so far this is what i have:
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
#include <cstring>
using std::strtok;
using std::strcat;
using std::strcpy;
void printPigLatin( char * );
int main()
{
char sentence[500];
char *token;
cout << "Enter string to tokenize and convert: ";
cin.getline( sentence, 500 );
token = strtok( sentence, " " );
cout << "\nPig latin for each token will be: " << endl;
while( token != NULL )
{
printPigLatin( token );
token = strtok( NULL, " " );
}
return 0;
}
void printPigLatin( char *word )
{
char temp[50];
for( int i = 0; *word != '\0'; i++ )
{
temp[i] = word[i + 1];
}
strcat( temp, "ay" );
cout << temp << endl;
}
I understand the tokenizing part quite clearly but I'm not sure how to do the pig latin.. i tried to start by simply adding "ay" to the token and see what the results will be .. not sure why the program goes into an infinite loop and keeps on displaying "ayay" .. any tips?
EDIT: this one works fine now but im not sure how to add the first letter of the token before adding the "ay"
EDIT: this is how i "see" it done but not sure how to correctly implement it ..
You're running over your input string with strcat. You need to either create a new string for each token, copying the token and "ay", or simply print the token and then "ay". However, if you're using C++ why not use istream iterators and STL algorithms?
To be honest, I severly doubt the quality of the C++ book, judging from your example. The “basic stuff” in C++ isn't the C pointer style programming. Rather, it's applying high-level library functionality. As “On Freund” pointed out, the C++ standard library provides excellent features to tackle your task. You might want to search for recommendations of better C++ books.
Concerning the problem: your printPigLatin could use the existing function strcpy (or better: strncpy which is safer in regards to buffer overflows). Your manual copy omits the first character from the input because you're using the i + 1st position. You also have a broken loop condition which always tests the same (first) character. Additionally, this should result in an overflow anyway.
As the people before me pointed out, there are several other methods of achieving what you want to do.
However, the actual problem with your code seems to be the use of strcat, I see that you changed it a bit in the edit. Here is an explanation of why the initial one did not work char* and size issues
Basically, the pointer does not allocate enough memory to add the "ay" to the string provided. If you create a pointer using the technique shown in the link, it should work fine.
I got your program to work, taking the strcat out and using
cout << word << "ay" << endl
Your loop is infinite because of *word != '\0'.
The word pointer is not changed at any time in the loop.
This seemed to have worked:
void printPigLatin( char *word )
{
cout << word + 1 << word[0] << "ay" << endl;
}
Just not sure if it's a good idea to do that.