字符串反转错误？

Question

I am creating this revese string App but i get a error if i include a space in the string !

#include <iostream>
#include <string>
using namespace std;

int main()
{
    int inputa;
    cout<<"%%%%%%%%%%%%%%%%%%String Reversing App%%%%%%%%%%%%%%%%%%%%%%%%"<<endl<<endl;

    cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl;
    cin>>inputa;
    if(inputa!=0)
    {

        do
        {

            string a,c="";

            cout<<"\nEnter the string you want to Reverse : ";
            cin>>a;
            for(int x=a.length()-1; x>=0; x--)
            {
                c=c+a.substr(x,1);
            }

            cout<<"\nThe Reverse String is : "<<c<<endl;

            cout<<"\nEnter 1 to continue and 0 to exit"<<endl<<endl;
            cin>>inputa;



        }
        while(inputa!=0);
    }
//not my  home work
}

If I type the following string like "abc def" there i get an error . But otherwise it works perfectly ! Is there some mistake with the codes ! I am new to CPP so it would be helpful if you could help me !

Answer 1

operator>> will stop reading at the first space (as David pointed out) - use getline instead

std::string a;
getline(std::cin, a);

Full edit of your code

#include <iostream>
#include <string>
#include <limits>

int main()
{
    std::cout << "%%%%%%%%%%%%%%%%%%String Reversing App%%%%%%%%%%%%%%%%%%%%%%%%\n\n";

    std::cout << "\nEnter 1 to continue and 0 to exit" << std::endl;
    int inputa;
    std::cin >> inputa;
    if(std::cin && inputa!=0)
    {
        std::cin.ignore(std::numeric_limits<int>::max( ), '\n');
        do
        {
            std::string a,c;

            std::cout<<"\nEnter the string you want to Reverse : ";
            getline(std::cin, a);
            for(int x=a.length()-1; x>=0; --x)
            {
                c+=a[x];
            }

            std::cout<<"\nThe Reverse String is : " << c << std::endl;

            std::cout << "\nEnter 1 to continue and 0 to exit" << std::endl << std::endl;
            std::cin >> inputa;
            std::cin.ignore(std::numeric_limits<int>::max( ), '\n');
        }
        while(std::cin && inputa!=0);
    }
}

Including David's verbatim answer because he answered with much more detail (David Rodríguez - dribeas) - please +1 him before he deletes it. His answer adds much more information that I did not mention so we are merging this into a single reply at Davids request,

The answer by Adrian is correct, deals with the immediate issue and provides a solution. As to why it enters an infinite loop, the reason is that after reading the first word, you are trying to read an integer std::cin >> inputa , which will fail as cde cannot be parsed as an integer. At this point the stream enters a fail state and subsequent reads will fail without doing anything (until you clear the error state).

What should you do?

If you want to process whole lines, then you should use std::getline , rather than operator>> . Beware on mixing both, as operator>> won't consume the spaces after the read (including new lines) and you might just read an empty line with the next std::getline . You can either always read with std::getline and then parse the line, or use ignore to clear up to the newline. Finally, whenever you perform IO operations, don't expect the operation to succeed: check the state of the stream. If you don't and your loop depends on IO to complete, it is quite easy to enter this sort of infinite loop, where the stream is marked as failed, no later reads succeed and you never break out of the loop.