# 11.5 Recursion vs. Iteration¶

- Both iteration and recursion are based on a control statement
  - Iteration uses an iteration statement
  - Recursion uses a selection statement
- Both involve iteration
  - Iteration explicitly uses an iteration statement
  - Recursion achieves iteration through repeated function calls
- Both involve a termination test
  - Iteration terminates when the loop-continuation condition fails
  - Recursion terminates when a base case is reached
- Both gradually approach termination
- Both can occur infinitely
  - An infinite loop occurs with iteration if the loop-continuation test never becomes false
  - Infinite recursion occurs if the recursion step does not reduce the problem in a manner that converges on the base case, or if the base case is mistakenly not tested

### Negatives of Recursion¶

- Recursion repeatedly invokes the mechanism, and consequently the overhead, of function calls
- Can be expensive in terms of both processor time and memory space
- Each recursive call causes another copy of the function’s variables to be stored in the stack frame
  - Can consume considerable memory space
- Iteration avoids these repeated function calls and extra memory assignments
- However, for some algorithms that are easily expressed and understood with recursion, iterative solutions are not readily apparent

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