If you want to get a little adventurous, try running your debugger. I assume you have one available. Step your code and see the values it takes at each step.

Could you post the current state of your code?

#include <ctime>
#include <cstdlib>
#include <iostream>
#include <string>

using namespace std;


int choice;
int randRange (int low, int high)

{
        return rand() % ( high - low ) + low;
    }

int main ()
{

 cout << "flip a coin? \n\n1: Yes\n\n2: No\n";
cin >> choice;

 while (!(choice == 1 || choice == 2))
 {
        cin >> choice;
        cout << "please enter 1 or 2";
 }
 if (choice == 1)
    {
            srand ( time( NULL ) );
            randRange( 1 , 10 );
            if (randRange( 1,10) >= 5)
            {
                cout << "Heads";
            }
else
            {
            cout << "Tails";
            }
    }
else if (choice == 2)
            {
            cout << "Boooo";
            return 0;
            }

}

Bugs:

- If people dont type in the right number you print out what to do only after they should have typed it in again, would be better the other way around.

- You uselessly call your randRange function twice without using the result of the first call.

Possible improvements:

- You can move the choice variable into main(), it doesnt need to be a global variable.

- Please try to consistently indent everything, as this makes reading the code easier. For example the "else" should be on same level as the "if" and all statements inside a block on same indendation level.

- If you want to modify it later with a loop to throw more than one coin its safer to put the srand call at the beginning of main so you dont accidently call it more than once. Calling it more than once would make the quality of random numbers worse.

int myInt = 0;
std::cin >> myInt;

#include <ctime>
#include <cstdlib>
#include <iostream>
#include <string>

using namespace std;

//Don't declare variables outside of functions (these are called 'globals'), it's a bad practice
//that while making things easier earlier on in programming, actually causes problems with more
//advanced programming.
//int choice;

int randRange (int low, int high)
{
    return rand() % ( high - low ) + low;
}

int main ()
{
    //srand() only needs to be called once for your entire program, so it's best to just
    //do so near the program start.
    srand ( time( NULL ) );
    
    cout << "flip a coin?\n1: Yes\n2: No\n";
    
    //Declare variables as close as possible to when you first use them, and also initialize 
    //them to a good default value - this makes it easier to detect bugs when they occur.
    int choice = 0; 
    cin >> choice;
    
    while (!(choice == 1 || choice == 2) )
    {
        //Incase of problems getting input, we check for if something went wrong with 'cin'.
        //'cin' has a special use of the '!' operator built in, that when used on 'cin',
        //lets you know if something went wrong.
        if(!cin)
        {
            std::cout << "Invalid input was given - it wasn't a number." << std::endl;
            
            //Since 'cin' was marked with a flag that said it got invalid input,
            //we need to clear that flag to let 'cin' know we saw and responded to the problem.
            cin.clear();
        }
        
        cin >> choice;
        cout << "please enter 1 or 2";
    }

    if (choice == 1)
    {
        randRange( 1 , 10 );
        if (randRange( 1,10) >= 5)
        {
            cout << "Heads";
        }
        else
        {
            cout << "Tails";
        }
    }
    else if (choice == 2)
    {
        cout << "Boooo";
        return 0;
    }
}

I was going to say the same, cout should be before the cin, it looks like the program is in an infinite loop but it isn't.

Also, some suggestions about the rest of the code:

• You should change the ">= 5" for either a ">= 6" or "a > 5". With ">= 5" you're taking 1, 2, 3 or 4 for "tails" and 5, 6, 7, 8, 9 and 10 for "Heads".
• Also, you can change it for something like "if (randRange(0,1) == 0)", it looks much clearer that there's a 50-50 chance for each value.
• If you checked that after the "while" the variable "choice" can be only a 1 or a 2, you can write if (choice == 1) { ... flip the coin ... } else { cout << "booo" }, you don't have to check again, if it's not a 1 then it can only be a 2. If you need to check the same variable for different values it's better to use a switch statement instead.
• The line "return 0;" shouldn't be there, it's only being executed if you typed "2". It should be only at the end of the main function if you'll always return a 0.

cin.ignore(std::numeric_limits<streamsize>::max());
cin.clear();

Is that correct?

Using cin.ignore(std::numeric_limits<streamsize>::max()); is highly inadvisable. This will not only flush the buffer of the current contents, but also tells the stream to sit there and eat up all future contents until EOF is hit. If you're going to use an EOF delimiter then set the number of ignored characters to something reasonable such as the number of characters still in the buffer. Otherwise if you're going to use std::numeric_limits<std::streamsize>::max() as the number of characters set the delimiter to something the user will actually put into the stream like '\n'.