10.2: Recursive Functions v.s. Loop Statements

In theory, any programming problem that can be solved with a looping statement can be solved with a recursive function and vice versa, because both techniques are recursion in nature. We begin our recursive function study by finding the recursive function solution of a programming problem that we have had a solution with a looping statement.

Example

First, we provide the solution of this problem by using a looping statement:

and a sample run of this program has following output:

Now, let's create a recursive version of this program. Following is the code of the recursive function along with a main() for testing purposes.

The recursive logic:

If the integer value the function receives is 1, then the function only asks a user to enter 1 number and return it as the sum.

If integer value the function receives more than 1, then the function also asks the user to enter 1 number, and call the function itself getSum() letting this function to ask the user to enter the rest of the numbers and return the sum of those numbers. When the function receives the return value of the function call getSum(), which is the sum of the rest of c-1 numbers the user entered, adds the number the user entered in this function, s, to the return value of the function getSum() to produce the sum of all the numbers user entered and return it (Line 15). As we can see, both functions produce the same solution:

Example

Again, we first provide a solution by using a looping statement:

The output of this program:

Now, let's create a recursive version of this function:

The output of this program:

Both functions provide identical solutions.

Logic:

If the integer the function receives is 1 (n==1), then just display this number which is 1.

If the integer the function receives is greater than 1 (n>1), then call the function itself, getSum(n-1) at Line 9, this function displays the number from 1 to n-1, and then, display the last number, which is n at line 10.

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