Help with some basic coding

[Spev]

I'm just trying to write a simple program in C++, yes it has to be C++.

 

I'm working on an if / else section. I have previously declared these variables. The program will ask the user to enter their favorite number under 20. If the number they enter is under 20 I want the program to assign that number to be equal to OfficialNumber, which I will reference later on in the program. If that user does not enter a number less than 20 as their favorite number I want the program to RE ASK the user to enter the number, I want this to keep repeating until the user finally enters a number that is under 20 thus allowing the program to continue. 

 

I know my else section is missing something. Need some help.

 

 

 

 

 

    cout << "What's your favorite number under 20?";

    cout << "\n";

    cin >> FavNumber;

 

if (FavNumber < 20)

    {

        OfficialNumber = FavNumber;

        cout << "Great! Next Question.";        //then I want it to progress to the next question.

    }

    else 

    {

        cout << "That's not a number under 20...try again please:";

        cout << "\n";

        cout << "What's your favorite number under 20?";

    }

[C1intFunWood]

Semicolon on the second last line and OfficialNumber = FavNumber. I may be wrong, I code Javascript

[zlolslavez]

I have no idea how to code this in C++, but I know if you were to code in Java, I was taught that you would do this by looping until something like "numberUnder20 = True", then continuing, Idk if you can do that though.

[Spev]

I have no idea how to code this in C++, but I know if you were to code in Java, I was taught that you would do this by looping until something like "numberUnder20 = True", then continuing, Idk if you can do that though.

I think you can I just haven't really learned about looping yet that's why I'm asking for help. 

[Spev]

Semicolon on the second last line and OfficialNumber = FavNumber. I may be wrong, I code Javascript

Uh yeah that's just an error on my part. It's not a problem with my program running that's an easy fix I'm just trying to figure out what to add at the end for my else statement.

 

Edit: Fixed 2 semicolon errors. Should be fine now.

[zMeul]

some random while loop sample; adapt it to your needs

while (n>0) {    cout << n << ", ";    --n;  }

[Menzenski]

you could use a do while loop to go back to the top if FavNumber isn't less than 20, just wrap the if else block in a do while loop with the condition of (FavNumber == 0 || FavNumber > 20).  (might need to check the logical operators its been a while since I've written c++).

[Spev]

some random while loop sample; adapt it to your needs

while (n>0) {    cout << n << ", ";    --n;  }

 

 

you could use a do while loop to go back to the top if FavNumber isn't less than 20, just wrap the if else block in a do while loop with the condition of (FavNumber == 0 || FavNumber > 20).  (might need to check the logical operators its been a while since I've written c++).

 

I apologize but if either of you could help me understand the while loop I would really appreciate it, I haven't used it before. I'm assuming it needs to start like this, but I don't know where to put this. Inside my else statement?

 

while (FavNumber >= 20)

{

 

?????

 

}

[zMeul]

the while loop

the while loop will execute the code in between { } for as long as the condition inside ( ) holds true

sorry if I can't explain it better, I haven't coded in more than 15y

this site should be helpful with sample code: http://www.cplusplus.com/

[Sauron]

This would work best with a while loop:

while(FavNumber > 20 || FavNumber < 0){   cout << "Invalid number\n";   cin >> FavNumber;} 

If you can't or won't use one, you can use the goto statement to return to the start if the number is invalid.

[h3Xx]

This would work best with a while loop:

while(FavNumber > 20 || FavNumber < 0){   cout << "Invalid number\n";   cin >> FavNumber;} 

If you can't or won't use one, you can use the goto statement to return to the start if the number is invalid.

 

if you want to be 100% correct it's better to use do..while to always enter first loop and avoid an uninitialized variable.

 

do{    cout << "Please give your favorite number under 20:" << endl;    cin >> FavNumber;} while (FavNumber < 0 || FavNumber > 20);

[Sauron]

 

if you want to be 100% correct it's better to use do..while to always enter first loop and avoid an uninitialized variable.

 

do{    cout << "Please give your favorite number under 20:" << endl;    cin >> FavNumber;} while (FavNumber < 0 || FavNumber > 20);

 

sure, I was assuming he had another line asking for a number before the loop - that way he could have the first sentence and then a dedicated "incorrect value" sentence

[Spev]

 

if you want to be 100% correct it's better to use do..while to always enter first loop and avoid an uninitialized variable.

 

do{    cout << "Please give your favorite number under 20:" << endl;    cin >> FavNumber;} while (FavNumber < 0 || FavNumber > 20);

Dude, that is awesome, I tried it in my code, I erase an entire if/else statement and a bunch of other mumbojumbo for these 4 lines and this basically did exactly what I needed it to do. If you could walk me through it I would greatly appreciate the logic behind this.

 

So the program prints the text and then asks for the user to enter FavNumber. I'm confused on the last statement. (FavNumber < 0 || FavNumber > 20), could you possibly explain how the compiler deals with this statement? What I'm trying to say as a beginner is I understand if/else statements really well. If is true and if the if statement isn't true the it's fault and runs the else code. I can see that logic on the screen through 2 different sections. However I don't understand this very well. Thank you for you help but I would be even more greatful if you could explain that line.

 

Also I am trying to fool proof my program. What if the user enters a number on accident? Is there a way to make the program re ask the question AGAIN if the user enters a number over 20 OR a letter or word?

[Spev]

 

if you want to be 100% correct it's better to use do..while to always enter first loop and avoid an uninitialized variable.

 

do{    cout << "Please give your favorite number under 20:" << endl;    cin >> FavNumber;} while (FavNumber < 0 || FavNumber > 20);

Also, when I run the code and use the number 20, it still works for 20, is there any way to make it only work for 19 and below? I can simply change the test to under 21....this is just a test program I'm creating, just for the principle and logic I'm trying to figure it out. I don't understand the || operator, an overload? Google is not my friend today I guess.

 

Edit: Figured this one out just changed the numbers a little bit lol it's been a long day.

[h3Xx]

Also, when I run the code and use the number 20, it still works for 20, is there any way to make it only work for 19 and below? I can simply change the test to under 21....this is just a test program I'm creating, just for the principle and logic I'm trying to figure it out. I don't understand the || operator, an overload? Google is not my friend today I guess.

 

Edit: Figured this one out just changed the numbers a little bit lol it's been a long day.

 

This

FavNumber < 0 || FavNumber > 20

Translates to: (if favNumber is lower than 0) OR (if favNumber is higher than 20) go inside the loop. If you don't want the 20 to be included you can easily say (if favNumber is equal or higher than 20) which is FavNumber >= 20.

 

Now if the user enters a string the compiler is going to convert it to an integer which is not possible because an integer has 4bytes and inside a string every character is one byte. So you will end up with garbage values. Pay attention that there is a possibility that a string might give a garbage value inside 0 to 20 and your program will think it is correct but this possibility is very unlikely to happen.