# What is the difference between recursion and Iteration?

· 4 min read

Both Recursion and Iteration execute the sequence of instructions repeatedly. When a statement in a function calls itself again, this is called recursion, and Iteration occurs when a loop executes the body repeatedly until the controlling condition becomes false. The critical distinction between recursion and Iteration is that recursion is a procedure always applied to a function. In contrast, We can apply Iteration to a sequence of instructions that we wish to run again.

## Understanding the Recursive Structure​

• We use a selection structure in recursion.
• If the recursion step does not reduce the issue in a way that converges on some condition (base case), infinite recursion occurs, and infinite recursion might crash the system.
• When a base case is detected, the recursion ends.
• Because of the complexity of maintaining the stack, recursion is often slower than Iteration.
• Iteration consumes less memory than recursion.
• Recursion reduces the size of the code.

Recursive JavaScript Approach:

``function pow(x, n) {  return n == 1 ? x : x * pow(x, n - 1);}console.log(pow(2, 3)); // logs 8``

## Understanding the Iterative Structure​

• If the loop condition test never returns false, iteration results in an infinite loop, and infinite looping wastes CPU cycles continually.
• The Iteration stops when the loop condition fails.
• Because Iteration does not require the stack, it is faster than recursion.
• Iteration consumes less RAM than recursion.
• Iteration makes the code longer.

Iterative JavaScript Approach:

``/*Iterative Function to calculate (w^y) in O(logy)*/function power(w, y) {  // Initialize result  let res = 1;  while (y > 0) {    // If y is odd, multiply x with result    if (y & 1) res = res * w;    // y must be even now    y = y >> 1; // y = y/2    w = w * w; // Change w to w^2  }  return res;}// Driver program to test the above functionslet w = 2;y = 3;console.log(`\${w} to the power of \${y} =` + power(w, y));// expected output: 8``

Simple Non-Iterative Approach: Exponentiation

``function pow(x, n) {  if (n === 1) {    return x;  } else {    x = x ** n;  }  return x;}console.log(pow(2, 3)); // 8``

## Which is preferable, Iteration or recursion?​

• It is sometimes more challenging to determine the temporal complexity of recursive code than iterative code.
• When compared to Iteration, recursion has a significant overhead. It is frequently slower since all function calls must be placed in a stack to allow the caller functions to return, and Iteration does not have this overhead.
• Endless recursive calls can cause a CPU to crash because infinite recursive calls can occur due to a mistake in the base condition, which never becomes false and keeps calling the function, resulting in a system CPU crash.
• Infinite Iteration because of a mistake in iterator assignment or incrementor, or in the termination condition, results in infinite loops, which may or may not result in system faults but ceases program execution.
• We can characterize every recursive call as a loop, which is what the CPU eventually performs. And more explicitly, recursion entails stacking the function calls and scopes. However, transforming your recursive approach to a looping one may require much work and make your code less manageable.

## Conclusion​

The difference between recursion and Iteration is that recursion is simply a function call. The function is being called by itself until a specific condition gets met, while Iteration is when a loop gets repeatedly executed until a specific condition gets met. A recursive solution is usually shorter than an iterative one.