Is it possible to embed "for loop" inside an "if statement" to compare multiple condition before continuing using c++

Question

In this program, the user must type in an 3 letter departing airport code (userFlight) and I will give them back the possible destinations. To check that what they typed in is one of the valid airport codes (departureAirport) I want to compare userFlight and make sure it is one of the possible departureAirports which I have stored in a vector called flights[]. This code obviously isn't working, but is there a similar way to accomplish this?

 if             
        (for (j = 0, j < flights.size, j++)
        {
        (userFlight != flights[j].departAirport)
        })

    {return errorCode};

else
    {//doSomething()};

deviantfan · Accepted Answer · 2015-12-11 04:21:23Z

6

If it has a operator< inside which does compare like your condition, how about

if(std::find(flights.begin(), flights.end(), userFlight) != flights.end())
{
    /* found */
}
else
{
    /* not found */
}

Else, if you don't like that, just check if the loop runs through all indices:

size_t i;
for (i = 0, i < flights.size, i++)
{
    if(userFlight == flights[i].departAirport)
        break;
}
if(i < flights.size)
{
    /* found */
}
else
{
    /* not found */
}

But no, a syntax like you want doesn't exist.

edited Dec 11, 2015 at 4:21

answered Dec 11, 2015 at 3:44

deviantfan

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2 Comments

Jorgel Over a year ago

Isn't it the other way aroud? If i < flights.size it was found

Tony Delroy Over a year ago

Separately, find needs operator== not operator<, and you need a predicate to check .departAirport unless you hack up the Flight class to have a bool operator==(const Airport&) const, which is an ugly idea IMHO - too easy to invoke accidentally in meaningless situations. With a predicate, you can simplify to my answer - std::any_of.

M.M · Accepted Answer · 2015-12-11 04:16:21Z

3

The code structure you were aiming for is:

for (j = 0; j < flights.size(); j++)
    if (userFlight == flights[j].departAirport)
        break;

if ( j == flights.size() )   // we got to the end
    return errorCode;

doSomething(j);

However, this is a C-like code style. Not that there is anything wrong with that, but C++ allows for algorithms to be expressed more abstractly (and therefore, easier to read and maintain). IMHO it would be better to use one of the other suggestions such as std::set or std::find_if.

answered Dec 11, 2015 at 4:16

M.M

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Comments

Bill Lynch · Accepted Answer · 2015-12-11 04:03:46Z

1

It sounds like you actually want to have a std::set of departing airports.

std::set<std::string> departing_airports = {"DTW", "MKE", "MSP", };
assert(departing_airports.count("DTW") == 1);

answered Dec 11, 2015 at 4:03

Bill Lynch

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Comments

Tony Delroy · Accepted Answer · 2015-12-11 04:37:36Z

1

Yet another option is std::any_of. Assuming flights contains objects of type Flight:

if (std::any_of(std::begin(flights), std::end(flights),
        [&](const Flight& f) { return userFlight == f.departAirport; }))
    return errorCode;

doSomething();

edited Dec 11, 2015 at 4:37

answered Dec 11, 2015 at 4:32

Tony Delroy

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