The code below is for storing a group of words in a std::vector and to count how many times a particular word given by the user appears in the vector by comparing it to all the words stored in the vector.
The console does not prompt me for input at the second std::cin >> in the program below.
#include <iostream>
#include <ios>
#include <iomanip>
#include <vector>
#include <algorithm>
using namespace std;
int main(int argc, const char * argv[])
{
cout<<"enter your words followed ny EOF"<<endl;
vector<string> words;
string x;
typedef vector<string>::size_type vec_size;
vec_size size;
while (cin>>x)
{
words.push_back(x);
}
size=words.size();
cin.clear();
//now compare
cout<<"enter your word:"<<endl;
string my_word;
int count=0;
cin>>my_word; //didn't get any prompt in the console for this 'cin'
for (vec_size i=0; i<size; ++i)
{
my_word==words[i]?(++count):(count=count);
}
cout<<"Your word appeared "<<count<<" times"<<endl;
return 0;
}
The final output I get is "Your word appeared 0 times".
What is the problem with the code. Any help would be great.
The program reads the word list until end of file. So, at a terminal, you can type the EOF character (Ctrl-D on Linux, Ctrl-Z Return on Windows), but what then?
I think after resetting the stream, a terminal will continue to read. But if the program is taking input from a disk file, pipe, etc., there is no hope. End-of-file is forever.
Instead, use some sort of sentinel, or prefix it by a count. That way the first loop can run until the logical end of the list. And then it can read the word intended for the summary logic.
while (cin>>x && x != '*') // The word "*" ends the list of words
{
words.push_back(x);
}
size=words.size();
//now compare
cout<<"enter your word:"<<endl;
while (cin>>x)
{
words.push_back(x);
}
Here, you're reading until failure. So, when this loop finishes, cin is in an error state. You need to clear the error state:
cin.clear();
http://www.cplusplus.com/forum/articles/6046/
Read this as an example and probable issues !!
Related
Why I can't take inputs of a string using gets,getline and cin.getline.when I debugg it seems that compiler skips those lines.here's my code-
#include <bits/stdc++.h>
using namespace std;
int main()
{
string s1,s2;
char *p;
int n,m,i;
cin>>n;
for(i=1;i<=n;i++)
{
int j=0;
getline (cin,s1);
getline (cin,s2);
cout<<s1<<"\n";
while(s1[j]!='\0')
{
if(s1[j]==' ')
{
s1.erase(s1[j]);
}
j++;
}
}
cout<<s1<<S2<<endl;
return 0;
}
What about j variable, it isn't set to zero when next for-loop iteration begin, so in second iteration you work with garbage.
Every time you use cin, it stores every character entered in memory until it encounters a newline character. This block of memory is called the input buffer.
when you take the input for 'n' the return key is in the cin buffer.
You should use cin.ignore to get rid of this newline.
Before getline (cin,s1); add cin.ignore statement
I need to make a program that reads n numbers in a row. For example, the user first puts in a list of 2 numbers like this:
P n
I managed to read those with scanf but now I need to read the n following numbers, these numbers are given in a row as follows.
1 6 3 99 ... n times
These numbers must be read all at once (or give the impression of).
I already tried using
while(getline(cin,str)){
// do something with str
}
As explained in this thread but I need the actions inside the while loop to stop when I hit the intro key. With my current implementation they don't stop, it just keeps waiting for more lines to read.
In summary:
First, user must be able to input two numbers (P and n)(done!) then hit enter and start typing a list of n numbers (not done!).
Here is my code.
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main(void){
int P,n;
scanf("%d %d",&P,&n);
string val;
int score[P];
int i;
for(i=0;i<P;i++){
score[i]=0;
}
while(getline(cin,val)){
printf("Val=%s\n",val.c_str());
stringstream stream(val);
int local;
while(stream >> local){
score[local]=score[local]+1;
printf("%d-%d\n",local,score[local]);
}
}
for(i=0;i<P;i++){
printf("%d-%d\n",i,score[i]);
}
return 0;
}
Use scanf() inside the n times loop instead of getline().
for(int i = 0; i < n; i ++){
scanf("%d",&variable);
}
Not sure I understood your question, but this code will read 2 numbers, then a line and then finish.
using namespace std;
int main(){
int P,n;
cin >> P;
cin >> n;
int *score = new int[P];
for(int i=0;i<P;i++){
score[i]=0;
}
int num;
string val;
cin.ignore();
getline(cin, val);
istringstream stream(val);
while (stream >> num) {
printf("Val = %d\n", num);
score[num]=score[num]+1; // potential segmentation fault here in your code
printf("%d-%d\n",num,score[num]);
}
delete [] score;
return 0;
}
The fault would occur because you are assuming that the number on the line is smaller than P, which is the size of the array. However, the following input would cause error:
1 2
5
This question is almost a classic. The classic question has this code:
cin >> n;
getline(cin, s);
and then the author is puzzled why s is empty. Your variation does the same, although it also uses C stdio function to make matters more confusing. The problem is that the first call is a field-based input, which will read a single value n and leave any other input in the buffer! If the user entered 42 and hit enter, the remaining input is the newline. The second getline() call then reads an empty string and discards the newline.
For interaction with the user, only use getline() and then try to parse each line. Using stringstreams or sscanf(), since you seem familiar with it, are both valid options. However, if you only want to read the input an not really interact, David Weston's suggestion is also a good one and probably the easiest one, too. However, since you're using C++, I'd suggest using cin >> variable instead.
I'm writing a function that reads line by line from cin and returns when it sees ; character.
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string.h>
using namespace std;
int read_cmd(char *cmd)
{
cout << "Please enter a string: \n";
cmd[0]='\0';
while(1){
char currentLine[10000];
currentLine[0]='\0';
cin.getline(currentLine,10000);
if (strcmp(currentLine,";")==0){
break;
}
strcat(cmd, "\n");
strcat(cmd, currentLine);
}
return 0;
}
int main(){
char cmd[1000];
while (1){
read_cmd(cmd);
cout<< cmd << endl;
}
}
I then tested it using text fed from another file via pipe.
./read_cmd < test_file
contents of test_file:
line 1
line 2
;
This outputs results just fine, however it gives me a segmentation fault at the end. Is there a way for cin to check if it's coming across an EOF and terminates?
To detect the EOF you should use something like:
while (cin.good() && !cin.eof())
{
// Read the file
}
See the documentation for cin, in particular the good() (for error checking) and eof() member functions.
In particular this example might be helpful.
I would highly suggest the use of the string object for something like this, that way you're not wasting space, as well as ensuring that you have enouch space. You can also do it without a loop.
string currentLine;
getline(cin, currentLine, ';');
Now, if you need to get just the last line with has the semi-colon, a loop is necessary, but still you can do it at little more easily.
string currentLine;
while(getline(cin, currentLine)){
if(currentLine.find(";") != string::npos){
break;
}
}
Use strings to pass things around as well. There's always the .clear() method as well that any string has for easy emptying.
string getline
string Object
I was asked to make a program that reads a cin could be text and then counts the words in it(i need to count as a word every name that can be accepted as a variable name ex _a,a1) my problem is that my code works for only one byte. if its more than one the sum is always 0.The only thing i think i can have wrong is that i didn't put the string into an array but a friend of mine told me i don't need to do so.below is my code:
#include<iostream>
#include<string>
#include<stdio.h>
using namespace std;
int main(){
int sum=0;
bool z= false; //z is just a switch to see if we are inside a word\n
string s;
cout<<"Insert text: ";
getline(cin,s); //here we get the string\n
int n=s.length()-1; //for some reason i==(s.length-1) put a warning$
for(int i=0;i==n;i++){ //here we check each byte to see what it contai$
cout<<s[i];
if(isalpha(s[i]) || s[i]=='_'){ //to enter a word we need a let$
z=true;
sum++;}
if(z==true){ // if we are in a word we can have numbers as w$
if(!isalnum(s[i]) && s[i]!='_'){
z=false;}} // exit the current word and go$
if(s[i]==EOF){ // the end\n
break;}}
cout<<"Number of words is: "<<sum<<endl; // the real end\n
return 0;
}
This is so much easier than the code you have provided. We can do this with the STL using an istream iterator. If you choose to use C++ and not C, then you should take advantage of the standard library.
#include <iostream>
#include <string>
#include <vector>
#include <iterator>
using namespace std;
int main(){
vector<string> words((istream_iterator<string>(cin)), istream_iterator<string>());
for(int i = 0; i < words.size(); i++)
cout << words[i] << '\n';
return 0;
}
Check your for loop.. it runs as long as the second statement is true.. when is it true that i==n? only at the very last byte.. change this to i<=n instead.
First of all you don't need dont use getline because it is insecure, use cin instead. Also you do not need the and use cin instead of getline. Also if getline is used with an array it could pose a serious problem and could be exploited via stack overflow. Sorry I cant help much what you were asking but I just wanted to give you a heads up.
I'm trying to collect user's input in a string variable that accepts whitespaces for a specified amount of time.
Since the usual cin >> str doesn't accept whitespaces, so I'd go with std::getline from <string>
Here is my code:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; i++)
{
string local;
getline(cin, local); // This simply does not work. Just skipped without a reason.
//............................
}
//............................
return 0;
}
Any idea?
You can see why this is failing if you output what you stored in local (which is a poor variable name, by the way :P):
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; i++)
{
string local;
getline(cin, local);
std::cout << "> " << local << std::endl;
}
//............................
return 0;
}
You will see it prints a newline after > immediately after inputting your number. It then moves on to inputting the rest.
This is because getline is giving you the empty line left over from inputting your number. (It reads the number, but apparently doesn't remove the \n, so you're left with a blank line.) You need to get rid of any remaining whitespace first:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
cin >> ws; // stream out any whitespace
for(int i = 0; i < n; i++)
{
string local;
getline(cin, local);
std::cout << "> " << local << std::endl;
}
//............................
return 0;
}
This the works as expected.
Off topic, perhaps it was only for the snippet at hand, but code tends to be more readable if you don't have using namespace std;. It defeats the purpose of namespaces. I suspect it was only for posting here, though.
Declare a character to get in the carriage return after you have typed in the number.char ws;int n;cin>>n;ws=cin.get();
This will solve the problem.
Using cin>>ws instead of ws=cin.get(),will make first character of your string to be in variable ws,instead of just clearing '\n'.
It's quite simple.
U jst need to put a cin.get() at the end of the loop.
Are you hitting enter? If not get line will return nothing, as it is waiting for end of line...
My guess is that you're not reading n correctly, so it's converting as zero. Since 0 is not less that 0, the loop never executes.
I'd add a bit of instrumentation:
int n;
cin >> n;
std::cerr << "n was read as: " << n << "\n"; // <- added instrumentation
for // ...
why this happens :
This happens because you have mixed cin and cin.getline.
when you enter a value using cin, cin not only captures the value, it also captures the newline. So when we enter 2, cin actually gets the string “2\n”. It then extracts the 2 to variable, leaving the newline stuck in the input stream. Then, when getline() goes to read the input, it sees “\n” is already in the stream, and figures we must have entered an empty string! Definitely not what was intended.
old solution :
A good rule of thumb is that after reading a value with cin, remove the newline from the stream. This can be done using the following :
std::cin.ignore(32767, '\n'); // ignore up to 32767 characters until a \n is removed
A better solution :
use this whenever you use std::getline() to read strings
std::getline(std::cin >> std::ws, input); // ignore any leading whitespace characters
std::ws is a input manipulator which tell std::getline() to ignore any leading whitespace characters
source : learncpp website
goto section (Use std::getline() to input text)
hope this is helpful
Is n properly initialized from input?
You don't appear to be doing anything with getline. Is this what you want?
getline returns an istream reference. Does the fact that you're dropping it on the ground matter?
On which compiler did you try this? I tried on VC2008 and worked fine. If I compiled the same code on g++ (GCC) 3.4.2. It did not work properly. Below is the versions worked in both compilers. I dont't have the latest g++ compiler in my environment.
int n;
cin >> n;
string local;
getline(cin, local); // don't need this on VC2008. But need it on g++ 3.4.2.
for (int i = 0; i < n; i++)
{
getline(cin, local);
cout << local;
}
The important question is "what are you doing with the string that gives you the idea that the input was skipped?" Or, more accurately, "why do you think the input was skipped?"
If you're stepping through the debugger, did you compile with optimization (which is allowed to reorder instructions)? I don't think this is your problem, but it is a possibility.
I think it's more likely that the string is populated but it's not being handled correctly. For instance, if you want to pass the input to old C functions (eg., atoi()), you will need to extract the C style string (local.c_str()).
You can directly use getline function in string using delimiter as follows:
#include <iostream>
using namespace std;
int main()
{
string str;
getline(cin,str,'#');
getline(cin,str,'#');
}
you can input str as many times as you want but one condition applies here is you need to pass '#'(3rd argument) as delimiter i.e. string will accept input till '#' has been pressed regardless of newline character.
Before getline(cin, local), just add if(i == 0) { cin.ignore(); }. This will remove the last character (\n) from the string, which is causing this problem and its only needed for the first loop. Otherwise, it will remove last character from the string on every iteration. For example,
i = 0 -> string
i = 1 -> strin
i = 2 -> stri
and so on.
just use cin.sync() before the loop.
just add cin.ignore() before getline and it will do the work
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; i++)
{
string local;
cin.ignore();
getline(cin, local);
}
return 0;
}