You have already seen a function that has called another function, but you may not have paid close attention to it. In the previous labs, you called a predefined function from the main. You also called the function get_input from the main function in the previous lab. In order to call a function inside another function, you need to have the declaration of the function that is being called before the declaration of the calling function.

Here is an example:

void that_function(double& x );

double this_function( ); //This function can
now call that function

int main( )

{

double y;

....

....

y = this_function( );

....

return 0;

}

double this_function( )

{

double x;

....

....

that_function(x
); // that function is
being called inside this function

return x;

}

void that_function(double& x )

{

....

....

}

**Exercise 4.4**

The following function will use **a, b, **and **c** as the coefficients
of a quadratic equation to compute **b**^{2} - 4**ac.**
This function calls on another function called *get_a_b_c* to get
the values for **a**, **b**, and **c.**

Write the complete program, ex43.cpp, compile and run it.

double bb_4ac( )

{

double a, b, c; //
Coefficients of a quadratic equation

get_a_b_c(a, b, c);

return b*b - 4*a*c;

}