C++ Fibonacci sequence - c++

Question

The program I am trying to make is supposed to calculate and display each entry of the fibonacci sequence up to the 40th.
I believe I'm nearly there in terms of getting this done. The issue is: after the numbers 1 and 2, the sequence just seems to reset itself and leaves every subsequent number 1 place behind in the sequence.
This is the code:
#include <iostream>
using namespace std;
int main()
{
int a = 0;
int b = 1;
for (int i = 0; i < 40; ++i)
{
if (i==1)
{
cout << i << " " << b << endl;
}
else if (i==2)
{
cout << i << " " << b*2 << endl;
}
else
{
int c = a + b;
a = b;
b = c;
cout << i << " " << c << endl;
}
}
return 0;
}
I pre-programmed the first couple of numbers in the sequence because I couldn't get them to work properly, but after doing this, it seems to throw off the rest of the program.
The output from the code is this:
0 1
1 1
2 2
3 2
4 3
5 5
6 8
7 13
8 21
9 34
10 55
11 89
12 144
13 233
14 377
15 610
16 987
17 1597
18 2584
19 4181
20 6765
21 10946
22 17711
23 28657
24 46368
25 75025
26 121393
27 196418
28 317811
29 514229
30 832040
31 1346269
32 2178309
33 3524578
34 5702887
35 9227465
36 14930352
37 24157817
38 39088169
39 63245986

Answer 1

It seems that I have solved this issue instantly after creating the post.
I decided to try pre-program the very first entry in the sequence (0) to be one, and completely remove the other pre-programmed parts in the sequence. This solved the entire thing.
Here's the working code:
#include <iostream>
using namespace std;
int main()
{
int a = 0;
int b = 1;
for (int i = 0; i < 40; ++i)
{
if (i == 0)
{
cout << i << " " << b << endl;
}
else
{
int c = a + b;
a = b;
b = c;
cout << i << " " << c << endl;
}
}
return 0;
}

Answer 2

You forgot to set a for the second case.
So when b = 2, c uses previous value of a which is 0.
Therefore, c = a+b = 0 + 2 = 2.
Set a = 1 in you second case:
else if (i==2)
{
a = 1 // This
cout << i << " " << b*2 << endl;
}

Answer 3

I pre-programmed the first couple of numbers in the sequence.. If you wish to go along this way, the following could be another method..
#include <iostream>
using namespace std;
int main()
{
int a = 0;
int b = 1;
cout << 0 << " " << a << endl;//simply display the preprogrammed numbers
cout << 1 << " " << b << endl;
for (int i = 2; i < 40; ++i)//apply the formula for remaining elements
{
int c = a + b;
a = b;
b = c;
cout << i << " " << c << endl;
}
return 0;
}

Answer 4

Try the following changes in your program.
#include <iostream>
using namespace std;
int main() {
int a = 0;
int b = 1;
for (int i = 0; i < 40; ++i)
{
if (i==0)
{
cout << i << " " << a << endl;
}
else if (i==1)
{
cout << i << " " << b << endl;
}
else
{
int c = a + b;
a = b;
b = c;
cout << i << " " << c << endl;
}
}
return 0;
}