How to Convert a Recursive Function or Algorithm to Non-Recursive?

Any recursive function can be converted to non-recursive function
through use of a stack as explained below.
  • A recursive call is similar to a call to another function.
  • Any call to a function requires that the function has
    storage area where it can store its local variables and actual parameters.
  • Return address must be saved before a call is made to a function.
  • Storage area for local variables, actual parameters and the
    return address can be provided through a stack.
  • In case of a recursive call, the value of local variables,
    parameters and the return address must be saved on the stack.
  • While returning from a nested call, the previous outer call
    must be recalled with resetting all the local variables and operation must
    resume from where it was suspended.
How to Convert a Recursive Function or Algorithm to Non-Recursive?

Rules for converting
a recursive algorithm to non-recursive one:

  • Declare stack – It will hold local variables, parameters,
    return address, etc.
  • The first statement after the stack initialization must have
    a label.

Steps required to
replace a recursive call:
  • Push all local variables and parameters into the stack.
  • Push an integer i into the stack, i gives the return
  • Set the value of formal parameters.
  • Transfer the control to the beginning of the function (i.e.
    first label immediately after initialization of stack) using goto. Use of goto
    is not a good practice but here we have no choice.
  • There should always be a label statement immediately
    following the recursive call. This label is the return address.

Steps required at the
end of recursive function:
  • If the stack is empty, then the recursion is finished.
  • Otherwise, pop the stack to restore the values of all local
    variables and parameters called by value.
  • Pop the return address.

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