C++ Validating Input with a while Loop

Summary

This tutorial demonstrates how to implement input validation using a while loop structure in a program. The program prompts users for their age, validates the input to ensure it's an integer, and provides a custom message based on the age. If the input is invalid, the program enters a loop, prompting the user to enter a valid number. The tutorial also addresses handling type mismatches and clearing the input stream to prevent endless loops, ensuring the program only continues with valid data.

Takeaways

• 🔁 The tutorial demonstrates using a while loop to validate user input in a program that asks for the user's age.
• 📢 The program provides a custom message based on the age input and asks if the user wants to run the program again.
• ❌ If non-integer data is entered, the program enters an endless loop due to a type mismatch.
• 🔍 To handle this, an inner while loop is introduced to ensure the input is an integer before proceeding.
• 💬 The program displays a 'must be a number' message if the input is not valid, prompting the user to try again.
• 🔄 The input stream is cleared and restored to a working state when an input failure occurs.
• 🗑️ The program uses 'cin.ignore' to discard the invalid input, either up to 100 characters or until a newline character is encountered.
• 🔒 The tutorial emphasizes the importance of input validation to prevent the program from entering an endless loop with incorrect data types.
• 📝 The script illustrates how to manage user input and error handling in programming, ensuring the program only processes valid data.
• 🔁 The tutorial concludes with the program successfully validating the user's input and continuing with its logic once valid data is entered.

Q & A

What is the main focus of the tutorial?

The tutorial focuses on input validation using a while loop structure in a program that asks for the user's age.

What happens when the user enters a valid age?

When the user enters a valid age, the program provides a custom message based on the age and asks if the user wants to run the program again.

What is the purpose of the inner while loop?

The inner while loop is used to ensure that the input is an integer. It continues to prompt the user until a valid integer is entered.

Why does the program go into an endless loop when non-integer data is entered?

The program goes into an endless loop because the input is not of the expected integer type, causing a type mismatch and failing to exit the loop.

How does the program handle input failure?

Upon input failure, the program uses a while loop to keep prompting the user until a valid number is entered. It also clears the input stream and discards the invalid input.

What is the significance of the 'C in clear' statement?

The 'C in clear' statement is used to clear the input stream and restore it to a working state after an input failure.

Why is it necessary to discard the invalid input?

Discarding the invalid input is necessary to prevent the program from continuously processing the wrong data type and to allow for new, valid input.

What is the role of the 'C and ignore' statement in the program?

The 'C and ignore' statement is used to ignore up to 100 characters or until a newline character is encountered, effectively discarding the invalid input.

How does the program ensure that the user is prompted again after an invalid input?

The program ensures that the user is prompted again by displaying a 'must be a number' message and then clearing the input stream before resuming the input prompt.

What is the final check the program performs after the user enters a number?

After the user enters a number, the program checks if it is a valid integer. If valid, the loop exits, and the program continues with the rest of the logic using the correct data type.

Outlines

00:00

🔁 Looping for Input Validation

This paragraph discusses a programming tutorial focused on input validation using a while loop structure. The program prompts the user to enter their age and provides a custom message based on the input. It includes a loop that continues to ask for the age until a valid integer is entered. The tutorial demonstrates the issue of an endless loop when non-integer data is inputted, causing a type mismatch. The solution involves using an inner while loop to check if the input is an integer, with the condition 'not C in age'. If the input is not an integer, the program displays a 'must be a number' message and continues to prompt for input until a valid number is provided. The tutorial also addresses the issue of the input stream entering a fail state when the data type does not match, causing the loop to continue indefinitely. The solution is to clear the input stream and ignore the incorrect input.

05:00

🛠️ Clearing Input Stream and Handling Invalid Data

The second paragraph delves into the solution for handling invalid data entries in the input stream. It explains how to clear the input stream using 'C in clear' to restore it to a working state. The tutorial then suggests using 'C and ignore' to discard the invalid input, either up to 100 characters or until a newline character is encountered. The paragraph demonstrates the importance of these steps in breaking out of an endless loop caused by invalid input. By clearing the input stream and ignoring the incorrect content, the program can then proceed with valid data in the 'age' variable, allowing it to perform the necessary condition checks and continue executing correctly.

Keywords

💡Input Validation

Input validation is the process of checking user input to ensure it conforms to expected formats or values. In the video, input validation is crucial for ensuring that the age entered by the user is an integer, preventing type mismatches and ensuring the program runs smoothly. The script describes how the program checks if the input is an integer and prompts the user until a valid input is received.

💡While Loop

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. In the context of the video, the while loop is used to continuously prompt the user for their age until a valid integer is entered. The script explains how a nested while loop is implemented to enforce input validation within the main loop.

💡Custom Message

A custom message is a user-specific response generated by a program based on user input. The video script describes how the program provides a custom message to the user based on their age after validating the input. For example, if the user enters 18, the program congratulates them and asks if they want to run the program again.

💡Type Mismatch

A type mismatch occurs when the data provided does not match the expected data type. In the video, a type mismatch is demonstrated when the user enters a non-integer value for age, causing the program to enter an endless loop. The script explains the importance of handling type mismatches to maintain program stability.

💡Endless Loop

An endless loop is a loop construct that continues to execute indefinitely without a terminating condition. The video script illustrates an endless loop scenario where the program repeatedly asks for the user's age due to incorrect data entry, highlighting the need for proper input validation to prevent such scenarios.

💡Integer

An integer is a whole number, positive, negative, or zero, without a fractional component. In the video, the script emphasizes the importance of ensuring that the user's age is entered as an integer to avoid type mismatches and to maintain the integrity of the program's logic.

💡Input Stream

An input stream is a sequence of data that a program reads from an external source, such as user input. The video script discusses how an input stream can enter a fail state when the data entered does not match the expected type, causing the program to loop indefinitely. The script also explains how to clear and restore the input stream to resolve this issue.

💡Fail State

A fail state refers to a condition where a program encounters an error or unexpected input that prevents it from proceeding as intended. In the video, the script describes how the input stream enters a fail state when the user enters non-integer data, which is then resolved by clearing the input stream and prompting the user again.

💡Data Type

A data type defines the kind of data that a particular variable can hold. In the video, the script focuses on ensuring that the user's age is entered as an integer data type. The program checks the data type of the input and prompts the user until the correct data type is provided, illustrating the importance of data type matching in programming.

💡Clear and Restore

Clearing and restoring an input stream refers to the process of resetting the input buffer and preparing it to receive new input. In the video, the script explains how to clear and restore the input stream after encountering a type mismatch, allowing the program to continue functioning correctly and prompting the user for valid input.

Highlights

Introduction to using input validation with a while loop structure.

Demonstration of a program that asks for the user's age and provides a custom message based on the input.

Explanation of how the program continues to loop until the user decides not to run it again.

Example of the program going into an endless loop when non-integer data is entered.

Discussion on the importance of handling type mismatches in data entry.

Introduction of a nested while loop to ensure the age input is an integer.

Use of 'not C in age' condition to check if the input is not an integer.

Moving the 'C out' statement before the while loop to prompt the user for input.

Clarification on the need to display a message before checking for input validity.

Observation of the program entering an endless loop due to input failure.

Explanation of how the input stream fails when the data type does not match the variable.

Solution to clear the input stream and restore it to a working state.

Use of 'C and ignore' to discard the incorrect input and continue the program.

Running the program again with the implemented fixes to handle non-numeric input.

Final demonstration of the program successfully validating the age input and continuing with condition checks.

Transcripts

hi in this tutorial we're going to look

at some input validation along with our

while loop structure so what I have here

is a program that asks the user how old

they are and we get their age in from

the keyboard and then based on the

number that they input we give a custom

message back out to them and then we're

asking them if they want to go again if

they want to put in another number and

if that's the case if they say yes then

it's going to start this whole loop

again and ask them for their age so just

to give you a quick run-through if I put

in a number that's 18 it says

congratulations do you want to run the

program again so if I say yes and I can

put in another number I get a different

message based on the age that I put in

and if I put in anything other than a Y

then it's going to end the program now

if I run this again and this time I put

in something like maybe I got mixed up

here and I type in a wife or how old I

am then you notice here that the program

is going haywire it's just an endless

loop running over and over and over

again and that is because age is

supposed to be an integer and I'm

putting in the wrong type of data so

it's a type mismatch so when it gets

through this loop and goes to run it

again and check these out

it just doesn't know how to handle that

wrong kind of data entry so what we want

to do is build into this a way of

checking to make sure that this is

actually an integer and I want it to

keep looping through putting in a number

until it actually

is a number and it is valid so I'm going

to use another while loop within this

while loop so I'm going to say while and

my condition check here is going to be

not C in H so I'm just going to grab

this move it up and I need another

parenthesis here so while not C in age

so CNH age is set up to be an integer so

if it's not right the exclamation point

not if this is not an integer type then

we're going to have some statements in

here so what I'll do is take this line

and I'm going to put it in where these

statements are and get rid of that

semicolon all right now let's run and

test this and see what happens and I

have a blank screen so why do we have a

blank screen well it's because when this

while if it hasn't gotten into this

point yet it's stopping for age and we

haven't given the user a message so I'm

going to take this C out statement and

move it before the while loop and then

instead of having this same message here

while it's not we'll say must be a

number right so we have to display this

before we can get to the CNH otherwise

it's just stopping here and waiting for

the user to type something in so let's

run it now we get our message how old

are you and I'll put in something that

is not a number and now it's a must be a

number but it's going wild again so it's

going over and over and over again into

an endless loop so why is that happening

what we have when we have input failure

right I put an put something in that

wasn't an integer so this starts a loop

it starts a while loop to keep going

over and over and over again but once

this happens age has the value that I

typed in at the keyboard which is the

wrong data type so there's nothing in

here that's clearing that out or

changing

what's in the age variable so I must

have a number in there and then what I

need to do is come in and we have an

input stream fail state right our data

doesn't match the variable type that

we're using so our input stream has

entered a fail state

so once in a fail state any other

statements input output statements that

are using that stream are ignored and so

the program continues to execute with

whatever values are already stored in

that variable and so this causes this

loop to continue so to fix that we need

to clear out whatever is in the input

stream so we're going to say C in clear

and that will clear out and restore the

input stream back to a working state and

then we want to drop and discard

whatever is in there that's in the CN

object so we're going to say C and

ignore C and ignore will ignore one

character but we don't really know how

many characters the user might have

typed in so we can put in I'm just going

to put up to a hundred because I doubt

whether they would do more than 100 in

this particular program and the other

argument that I can put in there is up

until a newline character so the way

this reads is in the CN object it's

going to clear it and restore it back to

a working state and then C and ignore

whatever is in the C and object we're

going to tell it to ignore up to 100

characters or until it reaches a newline

character and the newline character is

where the user has pressed enter so

let's try running this again and we'll

put in something again that is not a

number and now it says must be a number

so I'm putting in everything that's not

a number and then when I do put in a

number then it does exit this while loop

and then continue down with the rest of

our program which now has valid

information in the age variable and then

it can continue doing its condition

checks so this is using a while loop in

order to validate the data that's coming

in from the CN object and checking to

make sure that it is the right match for

the data type and if it's not we give

the user a message and then we clear out

whatever is in that and restore the

input stream and then drop and ignore

any Content that's in the CN object

already