How to Get a Variable from my MAIN function to another function?

I am defining a variable n using scanf in my main function. will the rest of my program know it?

I am solving an equation and have a square root part of my function that sends back the square root value to my main function.

Code:

double getSquareRoot ( void ); 


int main(void)
{
        double n_factorial; // powers multipled by the solved square root


        printf("ESTIMATE A FACTORIAL NUMBER\n");
        printf("This program was written by %s.\n", PROGRAMMER_NAME);


        printf("Please enter a positive integer: "):
        scanf("%lf", &n);


        sqrt_partial = (2.0 * n) + (1.0 + 3.0);


        sqrt_solved = getSquareRoot( );       
   
        n_factorial = pow(n,n) * exp(-n) * sqrt_solved;
        printf("%.0f! equals approximately %.5f \n", n, n_factorial);


return EXIT_SUCCESS;
}


double getSquareRoot (void)
{
        double n; // User defines the factorial
        double sqrt_partial; 
        double sqrt_solved;


        printf("Please enter a positive integer: "):
        scanf("%lf", &n);


        sqrt_partial = (2.0 * n) + (1.0 / 3.0);


        sqrt_solved = sqrt(sqrt_partial * PI);


        retun sqrt_solved;
}

You have to learn what the arguments of a function are.
You wrote

Code:

double getSquareRoot (void)

,where the void declares that this function has no arguments at all.When you want to pass an argument you have to write something like this

Code:

double getSquareRoot (typeOfArgument argumentName)

In your case you have a variable called n...but oops!You have not declare it!This is not f#,you have to say to the compiler the type of the variable.int is a probably good choice for n in this case.
So you can write

Code:

double getSquareRoot (int n)

Now n is visible by the body of getSquareroot.In other words ,n lives now and in the world of the function(not only in the world of main).

You could also set is a global variable ,but this is a really bad practice,especially if you are going to write a large program in the future.

> n_factorial = pow(n,n) * exp(-n) * sqrt_solved;
You see how you use n here.

> sqrt_solved = getSquareRoot( );
How about trying
sqrt_solved = getSquareRoot( n );