Calculating the factorial of a number is a classic example of a recursive function.

**Missing the Base Condition:**

```
#include <stdio.h>
int factorial(int n)
{
return n * factorial(n - 1);
}
int main()
{
printf("Factorial %d = %d\n", 3, factorial(3));
return 0;
}
```

Typical output: `Segmentation fault: 11`

The problem with this function is it would loop infinitely, causing a segmentation fault — it needs a base condition to stop the recursion.

**Base Condition Declared:**

```
#include <stdio.h>
int factorial(int n)
{
if (n == 1) // Base Condition, very crucial in designing the recursive functions.
{
return 1;
}
else
{
return n * factorial(n - 1);
}
}
int main()
{
printf("Factorial %d = %d\n", 3, factorial(3));
return 0;
}
```

Sample output

```
Factorial 3 = 6
```

This function will terminate as soon as it hits the condition `n`

is equal to 1 (provided the initial value of `n`

is small enough — the upper bound is `12`

when `int`

is a 32-bit quantity).

**Rules to be followed:**

- Initialize the algorithm. Recursive programs often need a seed value to start with. This is accomplished either by using a parameter passed to the function or by providing a gateway function that is non-recursive but that sets up the seed values for the recursive calculation.
- Check to see whether the current value(s) being processed match the base case. If so, process and return the value.
- Redefine the answer in terms of a smaller or simpler sub-problem or sub-problems.
- Run the algorithm on the sub-problem.
- Combine the results in the formulation of the answer.
- Return the results.

Source: Recursive Function

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