当用户输入“ enter”键时停止

Question

i've been writing a program that takes input from the user in two different "vectors" and stoping when enter key is hit.The code is given below

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

using namespace std;

int main()
{
    vector<string> a,c;
    string b;
    int m=0;//,words = 0;
    do
    {
        cin>>a[m];
        m++;
    }
    while(cin.get()!= '\n');

    int n=0;
    do
    {
        cin>>c[n];
        n++;
    }
    while(cin.get() != '\n');

    int mida=a.size()/2, midc=c.size()/2;
    int count;
    int i,j;

    for(i=0;i<n;i++)
        for(j=0;j<m;j++)
            {
                if(a[i] == c[j])
                count++;
            }

    if(count >= mida  || count >= midc)
        cout<<"similar"<<endl;
    else
        cout<<"dissimilar"<<endl;
    return 0;
}

Now the problem is that when i run the code after entering the words i need to put into the vector something like 'mango' 'orange' seperated by spaces, however as soon as i hit enter i get a segmentation fault. Could anyone tell me whats could possibly going wrong.

Answer 1

When you create a std::vector object, it starts out empty , its size will be zero and all indexing in it will be out of bounds and lead to undefined behavior (and probable crashes).

You can use push_back to append elements to the vectors. Like

std::string s;
std::cin >> s;
a.push_back(s);

---

While the above is the most likely reason for the crash you're having, it's not your only problem. Another is that each string of input might be ended with a newline. If you want to read a full line and then separate it into "words" then I suggest you use std::getline to read the full line, then use an std::istringstream to get the separate words from the line.

You can also use std::istream_iterator to easily append strings from an input stream to a vector.

You could do something like

std::string line;
std::getline(std::cin, line);
std::istringstream iss(line);

a = std::vector<std::string>(std::istream_iterator<std::string>(iss),
                std::string>(std::istream_iterator<std::string>());

Answer 2

cin>>a[m];

You are indexing past the end of the vector a . Because the vector hasn't been given a size, it has no space for even a[0] to be assigned.

A possible soution is to use a temporary variable to get the user input and then a.push_back[input] .