Problem of Using Cin Twice

Problem of using cin twice

Good writeup that explains some of the reasons why you are running into this issue, primarily due to the behavior of the input types and that you are mixing them

How to make it read cin twice?

I bet you did not read the i character from the input stream

Using cin.get(); Twice

cin.get(); retrieves a single character from the input. So if you have 5\n (\n being equivalent to pressing ENTER) on the input, cin.get(); will return 5, and another cin.get(); will return \n. If you are reading multiple numbers one after another, say in a while loop, if you forget about the \n character, you are likely going to run into issues.

Using cin.ignore(256, '\n'); can also correct this issue once you are done reading the characters you want or care about.

how can i use (!(cina)) twice times?

It seems you mean the following

#include <limits>

//...

if ( not ( std::cin >> arr[i] ) )
{
    //...
    std::cin.clear();
    std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
}

Problem while taking input using cin after detaching that thread in C++

In your case you should use atomic shared variables across threads.
The std::cin is blocking operation. In your code two seconds later doing detach for thread1. But std::cin still waiting for input...
The console window can std::cin or std::cout but not both at the same time so you need to change algorithm to avoid this problem.

cin double and string without space results in error

It's a bug in libc++ (reported back in 2013 I might add).

If a number is followed by a letter in an input stream without an intervening space, then reading this number may or may not fail, depending on the letter. The "bad" letters are A through F, I, N, P, and X (and their lower case counterparts).

An astute reader will notice that those are exactly the letters that can make up hexadecimal constants (yes P is one of them) and the words NAN and INF.

Among other characters that behave the same way are the plus sign, the minus sign, and the decimal point (the reason is obvious).

Cin making me enter twice

It's because you're asking them twice!

cin >> distanceTraveled;
while ((!(cin >> distanceTraveled)) ...

Try:

// assuming that distanceTraveled == 0 is invalid input
while ((cin >> distanceTraveled) && (distanceTraveled == 0))

And if you're trying to clear out any other input they entered on a line, you can use getline instead.

std::string junk;
std::getline(cin, junk);
std::cout << "ERROR:  invalid Entry.   Try again.\n\nHow far did ya go? ";

So the code would now look like this:

std::string junk;
std::cout << "How far did you go? ";
while ((cin >> distanceTraveled) && (distanceTraveled == 0)) 
{
    std::getline(cin, junk);
    std::cout << "ERROR:  invalid Entry.   Try again.\n\nHow far did ya go? ";
}

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