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
Related
I am a beginner in c++ and I want to enter a string as character by character into an array , so that I can implement a reverse function .. However unlike C when the enter is hit a '\n' is not insterted in the stream.. how can I stop data from being entered ?
my code is :
#include<iostream>
#include<array>
#define SIZE 100
using namespace std;
char *reverse(char *s)
{
array<char, SIZE>b;
int c=0;
for(int i =(SIZE-1);i>=0;i--){
b[i] = s[c];
c++;
}
return s;
}
int main()
{
cout<<"Please insert a string"<<endl;
char a[SIZE];
int i=0;
do{
cin>>a[i];
i++;
}while(a[i-1]!= '\0');
reverse(a);
return 0;
}
When you read character by character, it really reads characters, and newline is considered a white-space character.
Also the array will never be terminated as a C-style string, that's not how reading characters work. That means your loop condition is wrong.
To begin with I suggest you start using std::string for your strings. You can still read character by character. To continue you need to actually check what characters you read, and end reading once you read a newline.
Lastly, your reverse function does not work. First of all the loop itself is wrong, secondly you return the pointer to the original string, not the "reversed" array.
To help you with the reading it could be done something like
std::string str;
while (true)
{
char ch;
std::cin >> ch;
if (ch == '\n')
{
break; // End loop
}
str += ch; // Append character to string
}
Do note that not much of this is really needed as shown in the answer by Stack Danny. Even my code above could be simplified while still reading one character at a time.
Since you tagged your question as C++ (and not C) why not actually solve it with the modern C++ headers (that do exactly what you want, are tested, save and work really fast (rather than own functions))?
#include <string>
#include <algorithm>
#include <iostream>
int main(){
std::string str;
std::cout << "Enter a string: ";
std::getline(std::cin, str);
std::reverse(str.begin(), str.end());
std::cout << str << std::endl;
return 0;
}
output:
Enter a string: Hello Test 4321
1234 tseT olleH
This question already has answers here:
Why does std::getline() skip input after a formatted extraction?
(5 answers)
Closed 8 years ago.
Hi guys i am facing an unknown error while taking input from getline.My purpose is to take a number and two strings as input from the user and print the first string.Here is the problem code
#include <iostream>
using namespace std;
int main() {
int t;
cin>>t;
while(t--)
{ string s,p;
getline(cin,s);
getline(cin,p);
cout<<s;
}
return 0;
}
Now when i give input like:
1
abababa abb
b
it doesn’t print anything.Why is it happening?
After cin>>t, there is a newline remaining in the stream, then the newline will be assigned to s, so cout<<s seems to print nothing(Actually, it prints a newline).
add cin.ignore(100, '\n'); before first getline to ingore the newline.
Each time you use cin to get something like in cin >> t, it will leave a newline in the input buffer. so in next operation it will be affected by that and will seem to skip the "wait for return key" and hence abnormality. To avoid that usecin::ignore.
the documentation says:
Extracts characters from the input sequence and discards them, until
either n characters have been extracted, or one compares equal to
delim.
The function also stops extracting characters if the end-of-file is
reached. If this is reached prematurely (before either extracting n
characters or finding delim), the function sets the eofbit flag.
I have written your code in very understandable way but working
Let me know if you have any issue
#include <iostream>
using namespace std;
int main() {
int t=0;
cout<<"Enter t\n";
cin>>t;
cin.ignore();
while(t>0)
{ string s,p;
cout<<"Enter s\n";
getline(cin,s);
cout<<"Enter p\n";
getline(cin,p);
cout<<" Values s:"<<s<<" p:"<<p<<"\n";
t--;
}
return 0;
}
The newline from cin >> t; after pressing enter is still in std::cin when getline(cin,s) is called, resulting in s being empty. The string you enter is actually being stored in p. Try using a different capture method or flushing the cin buffer before using it again.
I think it's because getline() doesn't ignore the new line ccharacter, but it reads it in the next call yo getline. Try yo put a getline() before each calle, something like this:
Int main() {
int t;
cin>>t;
string s,p;
getline(cin,s);
while(t--)
{
getline(cin,s);
getline(cin, p);
getline(cin,p);
cout<<s;
}
Hope it helps :)
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 !!
i am doing a task where i am inputting ist no of times you want to have input and then i am inputting a full line by the use of getline but sime how i am not able to do that.
here when i try to input '1' as my no. of test cases it instantly gives '0' as answer and out of the loop why is not this cin>> test; here compatible with getline (cin,s);
#include<iostream>
#include<string>
using namespace std;
int main()
{
int test,j;
cin>>test;
int len;
string s;
for(j=1;j<=test;j++)
{
getline( cin,s);
len = s.length();
cout<<len;
}
return 0;
}
the difficulty
input :
1
output:
0
expected
input:
1
Hello World
output
11
Well I mixed a little C to get My answer
#include<iostream>
#include<string>
#include<cstdio>
using namespace std;
int main()
{
int test,j;
scanf("%d\n",&test);
int len;
string s;
for(j=1;j<=test;j++)
{
getline( cin,s);
len = s.length();
cout<<len;
}
return 0;
}
You are mixing formatted input and unformatted input functions.
operator>> leaves the trailing newline after the number you extracted in the input buffer, but this isn't a problem for subsequent reads done with operator>> because it skips all the whitespace it finds before reading. On the other hand, getline reads until it finds the delimiter (\n by default) without skipping anything.
Long story short: if you want to use getline you have to clean the buffer from the \n after your cin>>test;:
#include <limits>
// ...
cin>>test;
cin.ignore(numeric_limits<streamsize>::max(), '\n');
for(j=1;j<=test;j++)
{
getline( cin,s);
len = s.length();
cout<<len;
}
This is reading in the int and the string with the one carridge return.
It reads 1 as the total and then nothing as the string (hence the length of 0).
Try 1TEST and this should give you a length of 4.
I believe your problem is you are giving input stream as a parameter where you should give buffer.
Try this.
{
char szInput[256];
cin.getline( szInput,256);
len = strlen(szInput);
cout<<len;
}
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;
}