Swift Recursion
A function that calls itself repeatedly is known as recursive function and this technique is called recursion. When you create a recursive function, you must create a condition so that the function does not call itself indefinitely.
Example:
You can see in the above diagram that recursion is executed indefinitely. To get rid of these type of indefinite recursive, we use control statements.
Example: Swift 4 Program to print N positive numbers
Output:
Countdown: 6 5 4 3 2 1 0
You can see in the above program that the statement print(“Countdown:”) gives the output and the statement countDownToZero(num:3) calls the function that takes a parameter Integer.
The statement inside the function countDownToZero() executes and if the condition num > 0 is fulfilled, the function countDownToZero() is called again as countDownToZero(num: num – 1).
When the condition is not fulfilled, the function call is not done and the recursion stops.
Execution Steps
| Steps | Function call | Printed | Is num > 0 ? |
|---|---|---|---|
| 1 | countDownToZero(6) | 6 | Yes |
| 2 | countDownToZero(5) | 5 | Yes |
| 3 | countDownToZero(4) | 4 | Yes |
| 4 | countDownToZero(3) | 3 | Yes |
| 5 | countDownToZero(2) | 2 | Yes |
| 6 | countDownToZero(1) | 1 | Yes |
| 7 | countDownToZero(0) | 0 | No (Recursion Ends) |
Example2: Swift 4 program to find factorial of a number
Output:
The factorial of 6 is 720
Execution Steps
| Steps | Argument passed | Return statement | Value |
|---|---|---|---|
| 1 | 6 | return 6 * findFactorial(of:5) | 6 * findFactorial(of:5) |
| 2 | 5 | return 5 * findFactorial(of:4) | 6 *5 findFactorial(of:4) |
| 3 | 4 | return 4 * findFactorial(of:3) | 6 *5*4 findFactorial(of:3) |
| 4 | 3 | return 3 * findFactorial(of:2) | 6 *5*4*3 findFactorial(of:2) |
| 5 | 2 | return 2 * findFactorial(of:1) | 6*5*4*3*2 findFactorial(of:1) |
| 6 | 1 | return 1 | 6*5*4*3*2*1 |