How to break a for loop in Ternary Operator

Question

So, a method would be to cout<<""; if the condition is false but I don't feel like it's the right way and break doesn't seem to work. Is there something I should know ?

template <class T>
T get(const string &prompt) {
    cout<<prompt;
    T ret;
    cin>>ret;
    return ret;
}
   int main()
{
    vector<int>x;
        for(int i=0;i<1000;i++) x.push_back((rand()%1200+1200));
    int rating=get<int>("Your rating: ");x.push_back(rating);
        sortVector(x);
    for(int i=0;i<x.size();i++) ((x[i]==rating) ? cout<<"Found your rating on pozition "<<i : cout<<"");
}

Answer 1

Each part of the ternary operator must be able to evaluate to the same type*, so you can't have one part output (which will return the cout object) while the other break's.

Instead, in your situation, why don't you add the condition to your for?

for(int i = 0; i < x.size() && x[i] == rating; i++) {
    cout<<"Found your rating on pozition ";
}

But this might not be what you actually want

It seems you're trying to find an item's position in the array. If this is the case, and you're only looking for the first occurence, I'd suggest this instead:

int pos;
for(pos = 0; pos < x.size() && x[pos] != rating; pos++) { }

if(pos != x.size()) {
    cout<<"Found your rating on pozition " << pos;
} else {
    cout << "Couldn't find it!";
}

Or even better, use std::find!

---

^{*You could also have a throw in there. Thanks to @Lightness!}

Answer 2

Use of the conditional operator is not the best strategy for what you are trying to do.

Simplify your code. Use if-else.

for(int i = 0; i < x.size(); i++) 
{
   if (x[i] == rating)
   {
      std::cout << "Found your rating on position " << i << ".\n";
      break;
   }
   else
   {
      std::cout << "Still looking for your rating.\n";
   }
}

Answer 3

You don't.

Get rid of the crypticism, and write out a proper if statement like everybody else.

Answer 4

It's possible with the GNU statement-expression extension: ({ break; }) is an expression of type void.

But there is never reason to do that except in case of extreme macro hackery, which you probably shouldn't be doing yourself anyway.

Answer 5

You can't use break in a conditional. To hack this up using a non-throwing conditional (for educational purposes per your comments), you actually need it in the for loop as follows:

for (int i = 0; i < x.size(); i = x[i] == rating
                                  ? ((cout << "found at " << i), x.size())
                                  : i + 1)
    ;

What this does is advance i to x.size() (so the loop will terminate) when the rating is found (after evaluating output and ignoring it using the comma operator), otherwise moving i to the next element index (i + 1). Put another way, the use of the conditional operator above is equivalent to:

if (x[i] == rating)
{
    std::cout << "found at " << i;
    i = x.size(); // poor man's "break"
}
else
    i = i + 1;

(You could of course put the code immediately above in the statement controlled by your for loop... for (size_t i = 0; i < x.size(); ) if (x[i] == ...), but then you wouldn't be using the conditional operator (and could use an actual break, and might as well use ++i in the for advancement statement and ditch the else above, at which point you have R Sahu's answer).

I put a complete demo program on coliru.stacked-crooked.com.

---

As I mentioned in a comment, you can't break in a conditional, but you can throw. Using exceptions for an event you expect to occur is generally frowned upon (a coding convention that reserves them for unexpected events helps other programmers understand how you're expecting your program to run), but it's possible:

int main()
try
{
    ...
    for (size_t i = 0; i < x.size(); ++i)
        x[i] == rating ? throw i : (void)0;
}
catch (size_t i)
{
    std::cout << "found at " << i << '\n';   
}

You can find/run/edit this on coliru here. Note (void)0 is evaluated but does nothing - it has no side effects. You could use any expression there - 0, 'x', nullptr - but prefixing with (void) emphasises that the value can't and won't be read and used for anything. So it would be equivalent, clearer and more concise to use if (x[i] == rating) throw i; if we weren't set on using the conditional operator.

---

How you should actually write it if you're not trying to teach yourself how to abuse conditional operators:

std::cout << "found at " << x.find(rating) - x.begin() << '\n';

Often when you use find you should be checking against x.end() to see if your value was found, but in your case you know 100% that the value is in the vector so can safely keep the code simple.