I am trying to make a program although i have finished it already i need something more. So, the user asked to give an input IF the string contains * i want to erase the first * and cout the input
getline(cin,str);
int k=str.length();
for(int i=0; i<=k; i++)
if(str[i]=='*')
string::iterator it;
it=str.begin()+i;
str.erase(it);
break;
cout<<str<<endl;
what i am doing wrong ?
Be very careful, you need to use brackets {} to control scope, not tabulation!
Also, using = in a if is an assignation, not a check, you need to use ==
You iterate using i yet you delete using x?
You could simplify this by using std::find to remove the first occurrence of *:
str.erase(std::find(str.begin(), str.end(), '*'));
Related
I want to delete some words from a string but my code doesn't work . I don't have any errors or warnings , but I'm thinking that my string becomes empty. Could someone help me with this? I tried to convert my initial strings into 2 vectors, so that I can navigate more easily then
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string s("Somewhere down the road");
string t("down");
istringstream iss(s);
vector <string> plm;
vector <string> plm2;
do
{
string sub;
iss >> sub;
plm.push_back(sub);
} while (iss);
for(unsigned int i=0 ; i<plm.size();i++){
cout<<plm[i];}
istringstream ist(t);
do
{
string subb;
ist >> subb;
plm2.push_back(subb);
} while (ist);
for(int i=0;i<plm.size();i++){
for(int j=0;j<plm2.size();i++){
{if (plm[i]==plm2[j])
plm.erase(plm.begin()+j);}}}
for(int i=0 ; i<plm.size();i++)
cout<<plm[i];
}
Warning: this is really just a comment that's too long to fit in a comment field. Oh, and a bit of a rant at that.
I'm sure glad we have these modern languages to make life so much easier than it was decades ago. Consider, for example, what this job looked like an the long-since moribund SNOBOL 4 programming language:
s = 'somewhere down the road'
del s 'down' = :s(del)
OUTPUT = s
God, it's nice that we've since made so much progress that we don't have to deal with 3 whole lines of code, and we can now do the job with only 52 lines instead (oh, except that the 52 lines don't actually work, but let's ignore that for the moment).
I guess, in fairness, we can do the job a little more compactly in C++ though. One obvious way would be with std::remove_copy, some stream iterators, and a stringstream or two:
std::istringstream input("somewhere down the road");
std::string del_str("down");
std::istream_iterator<std::string> in(input), end;
std::ostringstream result;
std::remove_copy(in, end, std::ostream_iterator<std::string>(result, " "), del_str);
std::cout << result.str();
There is no benefit in converting to vector - string itself already provides all that is necessary for what you want to do. Anyway, do it this way:
vector<char> v;
v.assign(s.c_str(), s.c_str() + s.length()); // without...
v.assign(s.c_str(), s.c_str() + s.length() + ); // including...
// ... terminating null character
Now it gets easy:
size_t pos = s.find(t);
if(pos != string::npos)
{
s.erase(pos, t.length());
}
This does not care, however, about leaving multiple whitespace or if t is not an entire word within s (e. g. t = "down"; s = "I'm going to downtown."; would result in s == "I'm going to town."), but you did not do so either...
First problem is, if std::string::erase is called only with the beginning position, it erases everything until the end of string.
Second problem is, that the code will just erase all letters which are in the second string, one by one. I.e. not the entire word - for that, you would need to check if the entire word matches, and only then erase (the entire length of the word). Ask yourself - what will happen in the code, if e.g. the first two letters will match, but not the rest of the word?
In your second for loop you never incremented j and inside the if (plm[i]==plm2[j]) block you used j instead of i as your offset in erase().
for(int i=0;i<plm.size();i++)
{
for(int j=0;j<plm2.size();j++)//here you need to increment j
{
if (plm[i]==plm2[j])
plm.erase(plm.begin()+i);//here the offset should be i
}
}
Another thing don't use a do...while loop to read from the stringstream and push back on the vector. If the reading fails you will be pushing invalid data to the vector, instead try something like:
string sub;
while(iss >> sub;)
plm.push_back(sub);//only if reading is successful
...//do the same for the other istringstream too
You do not increment j this is the first thing I saw on your code. Write it correctly then if it still doesnt work, then ask!
I want to split the string into two separate strings based on the last '.'
For example, abc.text.sample.last should become abc.text.sample.
I tried using boost::split but it gives output as follows:
abc
text
sample
last
Construction of string adding '.' again will not be good idea as sequence matters.
What will be the efficient way to do this?
Something as simple as rfind + substr
size_t pos = str.rfind("."); // or better str.rfind('.') as suggested by #DieterLücking
new_str = str.substr(0, pos);
std::string::find_last_of will give you the position of the last dot character in your string, which you can then use to split the string accordingly.
Make use of function std::find_last_of and then string::substr to achieve desired result.
Search for the first '.' beginning from the right. Use substr to extract the substring.
One more possible solution , assuming you can update original string.
Take char pointer, traverse from last.
Stop when first '.' found, replace it with '\0' null character.
Assign char pointer to that location.
now you have two strings.
char *second;
int length = string.length();
for(int i=length-1; i >= 0; i--){
if(string[i]=='.'){
string[i] = '\0';
second = string[i+1];
break;
}
}
I have not included test cases like if '.' is at last, or any other.
If you want to use boost, you could try this:
#include<iostream>
#include<boost/algorithm/string.hpp>
using namespace std;
using namespace boost;
int main(){
string mytext= "abc.text.sample.last";
typedef split_iterator<string::iterator> string_split_iterator;
for(string_split_iterator It=
make_split_iterator(mytext, last_finder(".", is_iequal()));
It!=string_split_iterator();
++It)
{
cout << copy_range<string>(*It) << endl;
}
return 0;
}
Output:
abc.text.sample
last
I've just solve this problem:
http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=3139
Here's my solution:
https://ideone.com/pl8K3K
int main(void)
{
string s, sub;
int f,e,i;
while(getline(cin, s)){
f=s.find_first_of("[");
while(f< s.size()){
e= s.find_first_of("[]", f+1);
sub = s.substr(f, e-f);
s.erase(f,e-f);
s.insert(0, sub);
f=s.find_first_of("[", f+1);
}
for(i=0; i<s.size(); i++){
while((s[i]==']') || (s[i]=='[')) s.erase(s.begin()+i);
}
cout << s << endl;
}
return 0;
}
I get TLE ,and I wanna know which operation in my code costs too expensive and somehow optimize the code..
Thanks in advance..
If I am reading your problem correctly, you need to rethink your design. There is no need for functions to search, no need for erase, substr, etc.
First, don't think about the [ or ] characters right now. Start out with a blank string and add characters to it from the original string. That is the first thing that speeds up your code. A simple loop is what you should start out with.
Now, while looping, when you actually do encounter those special characters, all you need to do is change the "insertion point" in your output string to either the beginning of the string (in the case of [) or the end of the string (in the case of ]).
So the trick is to not only build a new string as you go along, but also change the point of insertion into the new string. Initially, the point of insertion is at the end of the string, but that will change if you encounter those special characters.
If you are not aware, you can build a string not by just using += or +, but also using the std::string::insert function.
So for example, you always build your output string this way:
out.insert(out.begin() + curInsertionPoint, original_text[i]);
curInsertionPoint++;
The out string is the string you're building, the original_text is the input that you were given. The curInsertionPoint will start out at 0, and will change if you encounter the [ or ] characters. The i is merely a loop index into the original string.
I won't post any more than this, but you should get the idea.
I'm having some trouble understanding how to use cin.getline and cin.get. I believe I understand the problem, just trying to figure out how to use them in conjunction possibly to solve a problem.
I'm reading from a text file that's read in through cin through command line.
I created a vector of vectors called spaceStation and I want to load it with characters.For example, here's a small portion of the file
M
4
2
//Possible comments
....
#...
E#..
#...
For this, i read in the first three characters properly just using cin>> to load into a variable. Now I need to create a loop to read these multiple characters in on the same line. 1) I'm supposed to ignore all comments 2) I want to run the while loop until a new line is reached that contains no more information
I created a string s so getline(cin,s) should load the entire lines. My question is should i create a cstring s so i can access the individual characters to load or is there a way to use cin.get() to extract the individual characters of the line received by s.
string s;
vector<string> v; // this is the best choice you can iterate like this to get char by char:
for (int i=0;i<v.size();i++)
for (int j=0;j<v[i].size();j++)
v[i][j];
// or like this to get strings
for (int i=0;i<v.size();i++)
v[i];
getline(cin, s); // this is to read the \n (new line) after int in the 3rd line
while (getline(cin,s))// till end of file
{
if (s.find_first_not_of(".#E") == -1)
{
v.push_back(s);
}
}
for (int i=0;i<v.size();i++)
cout<<v[i]<<endl;
You also can take advantage of the string class functions.
Ok so before I even ask my question I want to make one thing clear. I am currently a student at NIU for Computer Science and this does relate to one of my assignments for a class there. So if anyone has a problem read no further and just go on about your business.
Now for anyone who is willing to help heres the situation. For my current assignment we have to read a file that is just a block of text. For each word in the file we are to clear any punctuation in the word (ex : "can't" would end up as "can" and "that--to" would end up as "that" obviously with out the quotes, quotes were used just to specify what the example was).
The problem I've run into is that I can clean the string fine and then insert it into the map that we are using but for some reason with the code I have written it is allowing an empty string to be inserted into the map. Now I've tried everything that I can come up with to stop this from happening and the only thing I've come up with is to use the erase method within the map structure itself.
So what I am looking for is two things, any suggestions about how I could a) fix this with out simply just erasing it and b) any improvements that I could make on the code I already have written.
Here are the functions I have written to read in from the file and then the one that cleans it.
Note: the function that reads in from the file calls the clean_entry function to get rid of punctuation before anything is inserted into the map.
Edit: Thank you Chris. Numbers are allowed :). If anyone has any improvements to the code I've written or any criticisms of something I did I'll listen. At school we really don't get feed back on the correct, proper, or most efficient way to do things.
int get_words(map<string, int>& mapz)
{
int cnt = 0; //set out counter to zero
map<string, int>::const_iterator mapzIter;
ifstream input; //declare instream
input.open( "prog2.d" ); //open instream
assert( input ); //assure it is open
string s; //temp strings to read into
string not_s;
input >> s;
while(!input.eof()) //read in until EOF
{
not_s = "";
clean_entry(s, not_s);
if((int)not_s.length() == 0)
{
input >> s;
clean_entry(s, not_s);
}
mapz[not_s]++; //increment occurence
input >>s;
}
input.close(); //close instream
for(mapzIter = mapz.begin(); mapzIter != mapz.end(); mapzIter++)
cnt = cnt + mapzIter->second;
return cnt; //return number of words in instream
}
void clean_entry(const string& non_clean, string& clean)
{
int i, j, begin, end;
for(i = 0; isalnum(non_clean[i]) == 0 && non_clean[i] != '\0'; i++);
begin = i;
if(begin ==(int)non_clean.length())
return;
for(j = begin; isalnum(non_clean[j]) != 0 && non_clean[j] != '\0'; j++);
end = j;
clean = non_clean.substr(begin, (end-begin));
for(i = 0; i < (int)clean.size(); i++)
clean[i] = tolower(clean[i]);
}
The problem with empty entries is in your while loop. If you get an empty string, you clean the next one, and add it without checking. Try changing:
not_s = "";
clean_entry(s, not_s);
if((int)not_s.length() == 0)
{
input >> s;
clean_entry(s, not_s);
}
mapz[not_s]++; //increment occurence
input >>s;
to
not_s = "";
clean_entry(s, not_s);
if((int)not_s.length() > 0)
{
mapz[not_s]++; //increment occurence
}
input >>s;
EDIT: I notice you are checking if the characters are alphanumeric. If numbers are not allowed, you may need to revisit that area as well.
Further improvements would be to
declare variables only when you use them, and in the innermost scope
use c++-style casts instead of the c-style (int) casts
use empty() instead of length() == 0 comparisons
use the prefix increment operator for the iterators (i.e. ++mapzIter)
A blank string is a valid instance of the string class, so there's nothing special about adding it into the map. What you could do is first check if it's empty, and only increment in that case:
if (!not_s.empty())
mapz[not_s]++;
Style-wise, there's a few things I'd change, one would be to return clean from clean_entry instead of modifying it:
string not_s = clean_entry(s);
...
string clean_entry(const string &non_clean)
{
string clean;
... // as before
if(begin ==(int)non_clean.length())
return clean;
... // as before
return clean;
}
This makes it clearer what the function is doing (taking a string, and returning something based on that string).
The function 'getWords' is doing a lot of distinct actions that could be split out into other functions. There's a good chance that by splitting it up into it's individual parts, you would have found the bug yourself.
From the basic structure, I think you could split the code into (at least):
getNextWord: Return the next (non blank) word from the stream (returns false if none left)
clean_entry: What you have now
getNextCleanWord: Calls getNextWord, and if 'true' calls CleanWord. Returns 'false' if no words left.
The signatures of 'getNextWord' and 'getNextCleanWord' might look something like:
bool getNextWord (std::ifstream & input, std::string & str);
bool getNextCleanWord (std::ifstream & input, std::string & str);
The idea is that each function does a smaller more distinct part of the problem. For example, 'getNextWord' does nothing but get the next non blank word (if there is one). This smaller piece therefore becomes an easier part of the problem to solve and debug if necessary.
The main component of 'getWords' then can be simplified down to:
std::string nextCleanWord;
while (getNextCleanWord (input, nextCleanWord))
{
++map[nextCleanWord];
}
An important aspect to development, IMHO, is to try to Divide and Conquer the problem. Split it up into the individual tasks that need to take place. These sub-tasks will be easier to complete and should also be easier to maintain.