break statement in c++ by pressing enter

Question

#include <iostream>
using namespace std;
int main()
{
    int n,t=0,k=0;
    cin>>n;
    char data[n][100];
    int num[n];
    for(int i=0;i<n;i++)
{
    while(1)
    {
        cin>>data[i][t];
        cout<<data[i][t]<<endl;
        if(data[i][t]=='\n') break;
        k++;
        if(k%2==1) t++;
    }
    cout<<i;
    num[i]=(t-2)/2;
    k=0;
t=0;
 }

    for(int i=0;i<n;i++)
    {
        while(1)
        {
            cout<<data[i][t];
            if(t==num[i]) break;
            t++;
        }
        t=0;
    }
}

here is the code I have written in c++ which gives the even numbered characters from the starting half of every word given by the user but when giving input after pressing enter the loop should break but the loop is not breaking

while(1)
{
    cin>>data[i][t];
    cout<<data[i][t]<<endl;
    if(data[i][t]=='\n') break;
    k++;
    if(k%2==1) t++;
}

what is actually in data[i][t] when it is supposed to break? — Matt Jordan, Jun 13 '16 at 19:49
You're assuming `cin` will by default include newlines with the data read in from the stream. This is incorrect. — Captain Obvlious, Jun 13 '16 at 19:53
*here is the code I have written in c++* -- `cin>>n; char data[n][100];` -- This is not valid C++. Arrays must have compile-time sizes. — PaulMcKenzie, Jun 13 '16 at 19:55
Rather than searching for the end of the line yourself, [may I suggest `std::getline`](http://en.cppreference.com/w/cpp/string/basic_string/getline) to get the entire line and then parse the line [with a `std::stringstream`](http://en.cppreference.com/w/cpp/io/basic_stringstream)? This approach reduces this question to a near duplicate of [Read file line by line](http://stackoverflow.com/questions/7868936/read-file-line-by-line). — user4581301, Jun 13 '16 at 21:26

score 9 · Answer 1 · answered Jun 13 '16 at 19:53

By default formatted input using the "input" operators >> skip white-space, and newline is a white-space character. So what's happening is that the >> operator simply waits for some non-white-space input to be entered.

To tell the input to not skip white-space you have to use the std::noskipws manipulator:

cin>>noskipws>>data[i][t];

score 0 · Answer 2 · answered Jun 13 '16 at 22:53

There are some ways to implement in C++ what OP is trying to do. I'd start avoiding Variable Length Arrays, which aren't in the Standard and using std::strings and std::vectors instead.

One option is to read an entire line from input with std::getline and then process the resulting string to keep only the first half of even chars:

#include <iostream>
#include <string>
#include <vector>

int main() {
    using std::cin;
    using std::cout;
    using std::string;

    cout << "How many lines?\n";
    int n;
    cin >> n;


    std::vector<string> half_words;
    string line;
    while ( n > 0  &&  std::getline(cin, line) ) {
        if ( line.empty() )     // skip empty lines and trailing newlines
            continue;
        string word;
        auto length = line.length() / 2;
        for ( string::size_type i = 1; i < length; i += 2 ) {
            word += line[i];
        }
        half_words.push_back(word);
        --n;
    }

    cout << "\nShrinked words:\n\n";
    for ( const auto &s : half_words ) {
        cout << s << '\n';
    }

    return 0;
}

Another is, as Joachim Pileborg did in his answer, to disable skipping of leading whitespaces by the formatted input functions with std::noskipws manipolator and then read a char at a time:

// ...
// disables skipping of whitespace and then consume the trailing newline
char odd, even;
cin >> std::noskipws >> odd;

std::vector<string> half_words;
while ( n > 0 ) {
    string word;
    // read every character in a row till a newline, but store in a string
    // only the even ones
    while (    cin >> odd  &&  odd != '\n'
            && cin >> even && even != '\n' ) {
        word += even;
    }
    // add the shrinked line to the vector of strings
    auto half = word.length() / 2;
    half_words.emplace_back(word.begin(), word.begin() + half);
    --n;
}
//  ...

break statement in c++ by pressing enter

2 Answers2