Problems using cin in C++ - c++

Question

So, I've just begun learning c++, and i've been watching some tutorials, etc. I wrote a small program that should act like a magic eight ball, however I'm having some troubles with the cin command. I've written cin >> x; where x is a string, and when the user types their question, the program is supposed to print a random response. Sounds simple enough, but if the user types more than 1 word in the question, more than 1 response is printed. So, if i type "Will I live to be 100?" I get 6 answers instead of 1. Here's my code: (I'm sure it's probably messy and not very well organized or coded in the most efficient way, like I said, I'm a beginner.)
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
string z = "Yes";
string b = "Signs point to yes";
string c = "It is certain";
string d = "It is decidedly so";
string e = "Without a doubt";
string f = "Yes, definitely";
string g = "You may rely on it";
string h = "As I see it yes";
string i = "Most likely";
string j = "Outlook good";
string k = "Reply hazy try again";
string l = "Ask again later";
string m = "Better not tell you now";
string n = "Cannot predict now";
string o = "Concentrate and ask again";
string p = "Don't count on it";
string q = "My reply is no";
string r = "My sources say no";
string s = "Outlook not so good";
string t = "Very doubtful";
string u;
int main()
{
srand(time(0));
cout << "Ask A Question" << endl << endl << "Type 'Exit' to end the program" << endl << endl;
int a = 1+(rand()% 20);
cin >> u;
if (u == "Exit"){
return 0;
}
if (u == "exit"){
return 0;
}
if (a == 1){
cout << z << endl << endl;
main();
}
if (a == 2){
cout << b << endl << endl;
main();
}
if (a == 3){
cout << c << endl << endl;
main();
}
if (a == 4){
cout << d << endl << endl;
main();
}
if (a == 5){
cout << e << endl << endl;
main();
}
if (a == 6){
cout << f << endl << endl;
main();
}
if (a == 7){
cout << g << endl << endl;
main();
}
if (a == 8){
cout << h << endl << endl;
main();
}
if (a == 9){
cout << i << endl << endl;
main();
}
if (a == 10){
cout << j << endl << endl;
main();
}
if (a == 11){
cout << k << endl << endl;
main();
}
if (a == 12){
cout << l << endl << endl;
main();
}
if (a == 13){
cout << m << endl << endl;
main();
}
if (a == 14){
cout << n << endl << endl;
main();
}
if (a == 15){
cout << o << endl << endl;
main();
}
if (a == 16){
cout << p << endl << endl;
main();
}
if (a == 17){
cout << q << endl << endl;
main();
}
if (a == 18){
cout << r << endl << endl;
main();
}
if (a == 19){
cout << s << endl << endl;
main();
}
if (a == 20){
cout << t << endl << endl;
main();
}
return 0;
}

Answer 1

The problem is that you are calling main() over and over (recursively) in order to let the user ask another question. However, you don't take into account that std::cin stops extracting a string when it encounters a space, so you will end up making as many repetitions as there are whitespace-separated words in the user input.
Apart from this problem, the code is horrible. Sorry, it just is:
I. You declare 20 (or so) variables and a whole bunch of ifs instead of an std::vector<std::string>. This will quickly become unmaintainable if you have more elements or if you don't know the number of items.
II. You are calling main() recursively, which is legal but illegal and evil and shows a terribly bad programming style. Just don't do it. Use a loop (iterations) instead.
III. You are abusing namespace std; which is also discouraged.
IV. You are also using global variables with no good reason.
All in all, you should rewrite your program so that it reads something like this:
#include <vector>
#include <iostream>
#include <cstdlib>
#include <ctime>
int main()
{
std::vector<std::string> v;
v.push_back("Yes");
v.push_back("Signs point to yes");
v.push_back("It is certain");
v.push_back("It is decidedly so");
v.push_back("Without a doubt");
v.push_back("Yes, definitely");
v.push_back("You may rely on it");
v.push_back("As I see it yes");
// etc.
char q[0x100] = { 0 };
while (true) {
std::srand(std::time(nullptr));
int idx = rand() % v.size(); // this isn't perfect either, by the way
std::cout << "Ask a question:" << std::endl;
std::cin.getline(q, sizeof(q));
if (std::string(q) == "exit")
break;
std::cout << v[idx] << std::endl;
}
return 0;
}
And boom, it's just 37 lines instead of 128, and it's much readable.

Answer 2

cin reads a string just till the space is reached so basicly "Will I live to be 100?" contains 6 strings.
In order to avoid your problem use getline
Also you should better change your 20 string variables to a single array or vector of strings. In this case your main() will also look better as you will end up having just ONE if statemnt which will access an element of your array\vector depending on the random value.
Also you should move your global variables to main() and insert your code in a while loop which will have the following condition while (cin >> u && u != "exit") (leave only your variables declarations and srand(time(0)); outside the loop)
This answer shows how your program should actually look like.

Answer 3

Use getline to read a complete line

Answer 4

The problem here, among arguably others, is that cin stops whenever it encounters a space, and your stdin has already buffered that entire question (line), so the next time you call cin actually it reads what you had in the stdin buffer.
You should consider using getline function, that reads until a line break/carriage return.
getline(cin,u);
You should also consider learning loops, to not call main() again, and arrays for better structuring your code.