How do I limit the user input on the number of variable I want ?
ie
#include <iostream>
#include <cmath>
#include <iomanip>
#include <string>
using namespace std;
int main{
char variable1, variable2, variable3;
cin >> variable1 >> variable2 >> variable3;
}
If the user input 2 3 4 5, i don't want the 4th value to go into the next input i have. Any idea?
I have tried using setw(10) to limit then but it seems doesn't work as well.
Try using different cins (separate ones) for example:
cin>>variable1;
cin>>variable2;
cin>>variable3;
This would prevent saving multiple variables and generate an error if a user types "4 5"
It's not quite simple, but it's wholly doable.
You need to ensure that your program stops reading the input stream after it gets the first 3 inputs, separated by whitespaces. If you work with "getline(t, param, delim)" instead of just "cin", you'll have more options available to you. In a nutshell, getline is a function in the library that lets you take (from_somewhere, to_somewhere, stop_reading_here). For you, you'll be reading in from the "cin" stream, so it should look something like this:
getline(cin, random_string_variable_name, ' ');
The third parameter, the delimiter, is a space between two apostrophes. It's telling the function that whatever it's read in through 'cin' ends when it gets to the first space. If you try this code:
#include <string>
#include <iostream>
using namespace std;
int main() {
string variable[3];
for (int i = 0; i < 3; i++)
getline(cin, variable[i], ' ');
for (int i = 0; i < 3; i++)
cout << variable[i] << " ";
}
you'll find that "1 2 3 4 5" would return "1 2 3 ". Tell me if you need explanation on the square brackets or "for" loops, though you really should google that first if you don't.
As you are writing "If the user input 2 3 4 5, i don't want the 4th value to go into the next input i have.", I think your main interest is not limiting the input, but avoiding negative effects from additional input. This can be achieved by reading the user input into one string and extraction the integers from the string:
#include <string>
#include <iostream>
using namespace std;
int main() {
string line;
getline(cin, line);
// parse line to extract the single numbers
}
Related
I am trying to create an vector <int> whose size is not pre-defined. It should take in numbers as long as there are numbers in the input terminal and should stop reading when I hit Enter. I tried many solutions including the ones given here and here. In the second case, I can enter a non-integer to terminate the input to the vector. If I use the first solution (code added below), it listens to the input indefinitely.
Code:
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <iterator>
using std::cout;
using std::cin;
using std::vector;
using std::string;
using std::istringstream;
int main()
{
//cout << "Enter the elements of the array: \n";
//vector <int> arr ( std::istream_iterator<int>( std::cin ), std::istream_iterator<int>() );
vector <int> arr;
string buf;
cout << "Enter the elements of the array: \n";
while(getline(cin, buf))
{
istringstream ssin(buf);
int input;
while(ssin >> input)
{
arr.push_back(input);
}
}
cout << "The array: \n";
for(size_t i = 0; i < arr.size(); i++)
{
cout << arr[i] << " ";
}
return 0;
}
1) I don't feel that typing in a character or a very large number to end listening to input is very elegant. However, the solution with istringstream seems to be the way to go. I am not sure why it doesn't work.
2) Is there any way to detect the Enter from keyboard to terminate listening to input? I tried using cin.get(), but it changed the numbers in the vector.
3) Any other methods or suggestions?
Let's take things one step at a time.
We want to read up until enter is pressed. That means you probably want to use std:getline to read a line.
Then you want to parse it, so you want to put the line into an istringstream.
Then you want to read numbers. While you're reading them, you apparently want to ignore anything other than digits, and you want to keep reading even if you get to a group of digits that can't be converted to a number.
That leaves a few things that aren't entirely clear, such as what to do with that input that's too large to convert? Do you want to just skip to the next? Do you want to read some digits as a number, then read remaining digits as another number?
Likewise, what do you want to do if you get something like "123a456"? Should it be skipped completely, read as "123" (and the "a456" ignored)? Should it be read as "123" and "456", and just the "a" ignored?
For the moment let's assume that we're going to read space-separated groups of characters, and convert all those to numbers that we can. If something is too big to convert to a number, we'll ignore it (in its entirety). If we have a group like "123a456", we'll read the "123" as a number, and ignore the "a456".
To achieve this, we can do something like this:
std::string line;
std::getline(infile, line);
std::istringstream input(line);
std::string word;
std::vector<int> output;
while (input >> word) {
try {
int i = std::stoi(word);
output.push_back(i);
}
catch (...) {}
}
For example, given input like: "123a456 321 1111233423432434342343223344 9", this will read in [123, 321, 9].
Of course, I'm just taking a guess about your requirements, and I haven't worked at making this particularly clean or elegant--just a straightforward implementation of one possible set of requirements.
Please see the comments from #LearningC and #M.M.
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <iterator>
using std::cout;
using std::cin;
using std::vector;
using std::string;
using std::istringstream;
int main()
{
vector <int> arr;
string buf;
int input;
cout << "Enter the elements of the array: \n";
getline(cin, buf);
istringstream ssin(buf);
while(ssin >> input)
{
arr.push_back(input);
}
cout << "The array: \n";
for(size_t i = 0; i < arr.size(); i++)
{
cout << arr[i] << " ";
}
return 0;
}
#include <iostream>
#include <string>
using namespace std;
int main()
{
int num;
cin >> num;
string s;
getline(cin, s);
cout << s << " " << num << endl;
return 0;
}
In this code if I input 3 and press enter, then s takes an empty string.
1) If it is taking the first character as a newline, then is there a possible solution of taking line as input after taking an integer as input?
2) If my input is 4567artyu then how it is deciding whether 7 has to go into the s or num ?
I recommend that you always read complete lines of input from your users. It will cause the least confusion.
Ask for input.
Use std::getline to read a line of input.
If you don't want a string but, say, an integer, use std::stoi or (more general) boost::lexical_cast to safely convert the input to your desired target type. This is where you catch poor inputs and complain at the user.
I don't think that many users, if prompted for a number, would expect that entering 42bananas would be accepted as 42 and the bananas part be “remembered” for later. It will most likely be a typo and the user will be happy to be asked to correct it.
For taking line as input after taking integer as input you can consider removing the stray '\n' character from the stream.
#include <iostream>
#include <string>
using namespace std;
int main()
{
int num;
cin >> num;
getchar();
string s;
getline(cin, s);
cout << s << " " << num << endl;
return 0;
}
This will do the trick.
For second question, it reads 4567 as integer, it will continue to read it as integer until limit of int is reached and if limit is reached it will not consider anything after that. Then it will put the maximum value of int in the variable num and null int the string s. If limit is not reached, then string will remain in the input stream as it is, and will be fetched by variable s.
Try using cin.clear before you accept string
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 new to C++, and I'm trying to write a short C++ program that reads lines of
text from a file, with each line containing one integer key and one alphanumeric string value (no embedded whitespace). The number of lines is not known in advance, (i.e., keep reading lines until end of file is reached). The program needs to use the 'std::map' data structure to store integers and strings read from input (and to associate integers with strings). The program then needs to output string values (but not integer values) to standard output, 1 per line, sorted by integer key values (smallest to largest). So, for example, suppose I have a text file called "data.txt" which contains the following three lines:
10 dog
-50 horse
0 cat
-12 zebra
14 walrus
The output should then be:
horse
zebra
cat
dog
walrus
I've pasted below the progress I've made so far on my C++ program:
#include <fstream>
#include <iostream>
#include <map>
using namespace std;
using std::map;
int main ()
{
string name;
signed int value;
ifstream myfile ("data.txt");
while (! myfile.eof() )
{
getline(myfile,name,'\n');
myfile >> value >> name;
cout << name << endl;
}
return 0;
myfile.close();
}
Unfortunately, this produces the following incorrect output:
horse
cat
zebra
walrus
If anyone has any tips, hints, suggestions, etc. on changes and revisions
I need to make to the program to get it to work as needed, can you please
let me know?
Thanks!
See it:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main()
{
string name;
int value;
ifstream myfile("text.txt", ifstream::in);
while(myfile >> value >> name)
cout << name << endl;
return 0;
}
You are having problems because you attempt to read each line twice: first with getline and then with operator>>.
You haven't actually used std::map in any regard, at all. You need to insert the integer/string pair into the map, and then iterate over it as the output. And there's no need to close() the stream.
Instead of using "! myfile.eof()" use this code it will help.
ifstream is;
string srg;
is.open(filename);
while(getline(is,srg))
{//your code
}
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;
}