reference function from another function

Question

I forgot how to reference another function into a function in C++? In python it is declare as a class so that I can use it.

double footInches(double foot)
{
 double inches = (1.0/12.00) * foot;
 return inches;
}

double inchMeter(double inch)
{
 double meter = 39.37 * (footInches(inch));
 return meter;
}

I want to reference footInches in inchMeter.

edited

here is the main program

int main()
{
 double feet, inch, meter, x = 0;

 cout << "Enter distance in feet to convert it to meter: " << endl;
 cin >> x;

 cout << inchMeter(x);

 return 0;

i think the last line is not correct. i want to get the x in footInches first, then go to inchMeter, and then return the answer from inchMeter.

Answer 1

By reference do you mean call?
You are calling the function correctly in your example, but you don't need the surrounding parenthesis.

So simply like this:

double inchMeter(double inch)
{
 double meter = 39.3700787 * footInches(inch);
 return meter;
}

If your functions exist in different .cpp files, or you need to reference a function that is defined later you can use a forward declaration.

Example:

a.cpp:

double footInches(double foot)
{
 double inches = foot * 12.0;
 return inches;
}

b.cpp:

double footInches(double foot); //This is a forward declaration

double inchMeter(double inch)
{
 double meter = 39.3700787 * footInches(inch);
 return meter;
}

Answer 2

The traditional way to "reference" an arbitrary function in C is to use a function pointer. You really don't need it here because you're not going to change the implementation of the toinches function at runtime, but if you need a "reference to a function" you do it like this:

//Declare a function type that does what you want.
typedef double (*inch_converter_t)(double foot)

double footInches(double foot)
{
 double inches = (1.0/12.00) * foot;
 return inches;
};

//Pass a function pointer to another function for use.
double inchMeter(double inch, inch_converter_t converter)
{
 double meter = 39.37 * (converter(inch)); //Making a function call with the pointer.
 return meter;
}

int main()
{
    inch_converter_t myConverter = footInches;
    doube result = inchMeter(42, myConverter); //Call with function pointer.
}