Fibonacci Series Program In C

Fibonacci Series generates subsequent number by adding two previous numbers. Fibonacci series starts from two numbers − F0 & F1. The initial values of F0 & F1 can be taken 0, 1 or 1, 1 respectively.

Fibonacci series satisfies the following conditions −

```Fn = Fn-1 + Fn-2
```

So a Fibonacci series can look like this −

F8 = 0 1 1 2 3 5 8 13

or, this −

F8 = 1 1 2 3 5 8 13 21

Algorithm

Algorithm of this program is very easy −

```START
Step 1 → Take integer variable A, B, C
Step 2 → Set A = 0, B = 0
Step 3 → DISPLAY A, B
Step 4 → C = A + B
Step 5 → DISPLAY C
Step 6 → Set A = B, B = C
Step 7 → REPEAT from 4 - 6, for n times
STOP
```

Pseudocode

```procedure fibonacci : fib_num

IF fib_num less than 1
DISPLAY 0

IF fib_num equals to 1
DISPLAY 1

IF fib_num equals to 2
DISPLAY 1, 1

IF fib_num greater than 2
Pre = 1,
Post = 1,

DISPLAY Pre, Post
FOR 0 to fib_num-2
Fib = Pre + Post
DISPLAY Fib
Pre = Post
Post = Fib
END FOR
END IF

end procedure
```

Implementation

Implementation of this algorithm is given below −

```#include <stdio.h>

int main() {
int a, b, c, i, n;

n = 4;

a = b = 1;

printf("%d %d ",a,b);

for(i = 1; i <= n-2; i++) {
c = a + b;
printf("%d ", c);

a = b;
b = c;
}

return 0;
}
```

Output

Output of the program should be −

```1 1 2 3
```
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