How Do I Read This Program And Get The Answer?

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C++

#include <iostream>
#include <iomanip>
using namespace std;

int fn(int a) {
	cout << a << "-";
	if ((a == 0) || (a == 1))
		return a;
	return fn(a - 1) + fn(a - 2);
}

int main() {
	int a = fn(4);
	cout << a << endl;
	return 0;
}

What are the steps for solving this question?

Posted 13-Dec-15 22:49pm

Member 12205682

Updated 14-Dec-15 0:05am

CPallini

v2

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OriginalGriff · Answer 1 · 2015-12-13T23:00:00

1) Open Visual studio.
2) Copy and paste the code into a new project.
3) Run the application.

Alternatively, walk through the code and work out what happens each time you execute a line based on the values the line started with.

This is your homework, not ours: so it's up to you to do this, not us.

CPallini · Answer 2 · 2015-12-14T00:16:00

You have to use yourself as a debugger.
Let's make together just the first steps, starting from main, of course, we have:

C++

int a = fn(4);

In order to assign the correct value to a we have to evaluate fn(4).

So, let's step into fn(4):

We can safely ignore the cout line.
The if condition evaluates to false, since 4 is neither 0 nor 1.
Eventually we reach the line
```
return fn(3) + fn(2);
```
This tell us we have to step again (and again) into fn, with different argument values, in order to know our final result.

I suppose it is enough to make you figure out how to complete the homework.

How Do I Read This Program And Get The Answer?

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