Exploring the concepts of recursion and return statements in JavaScript

Question

Exploring the concepts of recursion and return statements in JavaScript

Currently, I am immersing myself in the world of JavaScript by taking courses on CodeAcademy.com. However, there is one exercise question that is giving me some trouble, even though I believe I have come up with the correct answer.

This particular code is intended to assist individuals in determining how much change they should return when a purchase is made. It takes a number as input and then calculates the appropriate amount of quarters and pennies to give back.

My confusion lies here:

• Shouldn't the code cease running the first time it reaches line 11? If not, could you explain why?

• In case the code does indeed stop at line 11, why am I able to insert additional code after line 10 which executes three times before providing an output? Upon testing this, I realized that indeed, placing quarters += 1; after line 10 results in a return value of 6.

var change = 0;
var quarters = 0;
function howManyQuarters(howMuchMoney) {
  if (howMuchMoney < 0.25) {
    change = howMuchMoney;
    return 0;
  }
  else {
    quarters += 1;
    howManyQuarters(howMuchMoney-0.25);
    return quarters;  // << line 11
  }
}

change = 0.99;
console.log ("Pay out " + howManyQuarters(change) + " quarters");
console.log ("And you'll have " + change * 100 + " pennies left over");

javascript recursion

Answer 1

Answer №1

The reason the code doesn't halt execution on Line 11 initially is because upon reaching line 10 for the first time, it effectively loops back to line 3.

Visualize the recursive levels in this manner:

1. (Line 15) howManyQuarters(0.99)
    2. (Line 4) howMuchMoney exceeds 0.25...thus the else branch is taken
    3. (Line 10) howManyQuarters(0.74)  --> 0.74 = 0.99-0.25
        4. (Line 4) howMuchMoney surpasses 0.25...hence, move to else block
        5. (Line 10) howManyQuarters(0.49)  --> 0.49 = 0.74-0.25
            6. (Line 4) howMuchMoney is greater than 0.25...so else clause is executed
            7. (Line 10) howManyQuarters(0.24)  --> 0.24 = 0.49-0.25
                8. (Line 4) howMuchMoney falls below 0.25...enter main if section
                9. (Line 6) return 0;
            11. (Line 11) return quarters;
        12. (Line 11) return quarters;
    13. (Line 11) return quarters;
14. (Line 11) return quarters;

Answer 2

The reason the code doesn't halt execution on Line 11 initially is because upon reaching line 10 for the first time, it effectively loops back to line 3.

Visualize the recursive levels in this manner:

1. (Line 15) howManyQuarters(0.99)
    2. (Line 4) howMuchMoney exceeds 0.25...thus the else branch is taken
    3. (Line 10) howManyQuarters(0.74)  --> 0.74 = 0.99-0.25
        4. (Line 4) howMuchMoney surpasses 0.25...hence, move to else block
        5. (Line 10) howManyQuarters(0.49)  --> 0.49 = 0.74-0.25
            6. (Line 4) howMuchMoney is greater than 0.25...so else clause is executed
            7. (Line 10) howManyQuarters(0.24)  --> 0.24 = 0.49-0.25
                8. (Line 4) howMuchMoney falls below 0.25...enter main if section
                9. (Line 6) return 0;
            11. (Line 11) return quarters;
        12. (Line 11) return quarters;
    13. (Line 11) return quarters;
14. (Line 11) return quarters;

Answer 3

Answer №2

It's important to remember that recursion involves calling a function multiple times, and each call must complete before the function finishes executing. For example, if the function howManyQuarters is called three times, the code following each call (such as a return statement) will also be executed three times.

I hope this explanation clarifies things for you!

Answer 4

It's important to remember that recursion involves calling a function multiple times, and each call must complete before the function finishes executing. For example, if the function howManyQuarters is called three times, the code following each call (such as a return statement) will also be executed three times.

I hope this explanation clarifies things for you!

Answer 5

Answer №3

The true essence of recursion lies in the concept of a function calling itself repeatedly until a certain condition is met, at which point it ceases to call itself.

Although in this instance, the function does indeed halt at the return quarters; line, it has already initiated a self-call in the preceding line.

The critical stop condition serves to prevent an infinite loop by halting the function when the input number falls below 0.25. Therefore:

Illustrative examples:

If the initial value is less than 0.25, the function will execute only once and return 0.
If the initial value is between 0.25 and 0.5, the function will execute twice - the recursive call occurs once as the value exceeds 0.25, but upon subtracting 0.25, the subsequent call meets the stop condition with a value less than 0.25.

The result returned is tracked by a global variable defined outside the function, incrementing each time the function recurs. However, this approach may not be foolproof as demonstrated in this specific case - where executing the function again with the same change amount yields an incorrect outcome.

Answer 6

The true essence of recursion lies in the concept of a function calling itself repeatedly until a certain condition is met, at which point it ceases to call itself.

Although in this instance, the function does indeed halt at the return quarters; line, it has already initiated a self-call in the preceding line.

The critical stop condition serves to prevent an infinite loop by halting the function when the input number falls below 0.25. Therefore:

Illustrative examples:

If the initial value is less than 0.25, the function will execute only once and return 0.
If the initial value is between 0.25 and 0.5, the function will execute twice - the recursive call occurs once as the value exceeds 0.25, but upon subtracting 0.25, the subsequent call meets the stop condition with a value less than 0.25.

The result returned is tracked by a global variable defined outside the function, incrementing each time the function recurs. However, this approach may not be foolproof as demonstrated in this specific case - where executing the function again with the same change amount yields an incorrect outcome.

Answer 7

Answer №4

The concept of recursion is truly remarkable and powerful within the realm of computer science. A recursive function typically follows a consistent structure:

function myRecursive(nSizeData){
  if(baseCondition is TRUE){
    //execute the function with nSizeData
    //perform actions here
  }
  else{
    //invoke the function again with a smaller dataset
    //ensuring that it converges towards the base condition
    myRecursive(mSizeData);
  }
}

A crucial aspect is the presence of a base condition, which acts as the foundation of the function: when the input data satisfies this condition, the function can run without further recursion. Otherwise, it continues to call itself with reduced data sets. The recursive process can be visualized using a stack: each function call pushes onto the stack, while returning values pop off the stack. The initial pop will always correspond to the base condition evaluation.

Caution must be exercised, as failure to meet the base condition can lead to a stackoverflow error.

An exemplary illustration is the factorial function for integers:

function factorial(n){
  if(n==0 || n==1){
    return 1;
  }
  else{
    return factorial(n-1);
  }
}

For additional insights, refer to this resource.

Answer 8

The concept of recursion is truly remarkable and powerful within the realm of computer science. A recursive function typically follows a consistent structure:

function myRecursive(nSizeData){
  if(baseCondition is TRUE){
    //execute the function with nSizeData
    //perform actions here
  }
  else{
    //invoke the function again with a smaller dataset
    //ensuring that it converges towards the base condition
    myRecursive(mSizeData);
  }
}

A crucial aspect is the presence of a base condition, which acts as the foundation of the function: when the input data satisfies this condition, the function can run without further recursion. Otherwise, it continues to call itself with reduced data sets. The recursive process can be visualized using a stack: each function call pushes onto the stack, while returning values pop off the stack. The initial pop will always correspond to the base condition evaluation.

Caution must be exercised, as failure to meet the base condition can lead to a stackoverflow error.

An exemplary illustration is the factorial function for integers:

function factorial(n){
  if(n==0 || n==1){
    return 1;
  }
  else{
    return factorial(n-1);
  }
}

For additional insights, refer to this resource.

Answer 9

Answer №5

Upon each instance of the function being invoked, it must ultimately be concluded with a return statement. The following illustration illustrates this concept:

Initiate howManyQuarters.
  Initiate howManyQuarters.
    Initiate howManyQuarters.
      Initiate howManyQuarters.
      return
    return
  return
return

Answer 10

Upon each instance of the function being invoked, it must ultimately be concluded with a return statement. The following illustration illustrates this concept:

Initiate howManyQuarters.
  Initiate howManyQuarters.
    Initiate howManyQuarters.
      Initiate howManyQuarters.
      return
    return
  return
return

Answer 11

Answer №6

Apologies for veering off topic, but may I ask why you are using such a complex function for basic mathematical operations? You could achieve the same result with a one-line function (but with aggregated output).

function calculateAmount(val) {
    return [
        Math.floor(val / 0.25),
        parseFloat((val % 0.25).toFixed(2))
    ];
}

It can be simplified to this.

http://jsfiddle.net/semencov/D8xUE/

Answer 12

Apologies for veering off topic, but may I ask why you are using such a complex function for basic mathematical operations? You could achieve the same result with a one-line function (but with aggregated output).

function calculateAmount(val) {
    return [
        Math.floor(val / 0.25),
        parseFloat((val % 0.25).toFixed(2))
    ];
}

It can be simplified to this.

http://jsfiddle.net/semencov/D8xUE/

Answer 13

Answer №7

From my perspective, it seems that the

return quarters;

statement is not being executed immediately after line 10. Instead, when the program reaches the

howManyQuarters(howMuchMoney-0.25);

line, it calls itself recursively without processing line 11 at that moment. Only after all the recursive calls have been completed does the program exit each loop and move on to execute line 11.

Answer 14

From my perspective, it seems that the

return quarters;

statement is not being executed immediately after line 10. Instead, when the program reaches the

howManyQuarters(howMuchMoney-0.25);

line, it calls itself recursively without processing line 11 at that moment. Only after all the recursive calls have been completed does the program exit each loop and move on to execute line 11.

Exploring the concepts of recursion and return statements in JavaScript

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

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