Nested Else-Ifs Do Not Go Beyond The First Else-if

[HolyDoom Witch]

Now here is a wonderful code I made, that tells your age the same as was on your last birthday TILL one day before of your birthday (so computer-like no? but I too happen to think that way when it comes to age!). But, as you can see, the nested else-ifs don't go beyond the first else-if level. And I think this SHOULD work, especially when the first nested else-if works. (Nutty C++.)

One has to resort to if (condition && condition) to make it work.

Now WeaknessForCats explained something about why it won't work but that was in the last thread which was a different topic where I happened to start all this. So please paste your reply here, then I'll respond.

Though the point that should be taken here is that it won't work this way, and which is all that should matter.

Thanks

string name;
int day, month, year, b_day, b_month, b_year;
  cout <<"Enter your first name: "; cin >>name;
  cout <<"H! " <<name <<", what is the date today? Enter day (1 to 31): "; cin >>day;
  cout <<"Now enter the month (1 to 12): "; cin >>month;
  cout <<"And the year? (4 digits): "; cin >>year;
 
  cout <<"\nNow input your birth date the same way. Day: "; cin >>b_day;
  cout <<"Month: "; cin >>b_month;
  cout <<"Year: "; cin >>b_year;
 
if (month < b_month) cout <<"\nYour age is: " <<year - b_year - 1 <<" as of today on "
                          <<day <<"-" <<month <<"-" <<year <<".";
 
else if (month == b_month)
  { if (day < b_day) cout <<"\nYour age is: " <<year - b_year - 1 <<" as of today on "
                          <<day <<"-" <<month <<"-" <<year <<".";
  }
else if (month == b_month)
  { if (day == b_day) cout <<"\nHey... you became " <<year - b_year <<" years old today on "
                           <<day <<"-" <<month <<"-" <<year <<"... Happy Birthday!!";
  }
else cout <<"\nYour age is " <<year - b_year <<" as of today on "
          <<day <<"-" <<month <<"-" <<year <<".";
 

Would have been nice if these site people could provide an interpreter too!

[Rabbit]

It's not going to go to the next else if and check that condition because it only picks the first one where the condition is true.

Just move the code in the second else if into the first.

[HolyDoom Witch]

Well then, it can't be done, since that is not what is required: the first condition of the first else-if is not common to the every set henceforth.

[Rabbit]

It can be done. The first else if condition is exactly the same as the second else if condition. It is only the nested if that has differing conditions. And that's fine, it will still work.

[HolyDoom Witch]

Well yeah, that is common all right, but only in a three conditions, when day may be less, may be equal, or may be bigger than the birth day, and month equal to the birth month in all the three. But there will be a problem if today's month is BIGGER than the birth month. Because the first else-if condition implies that today's month be EQUAL to the birth month. Your style works till that point.

What's more is, say even if this code had gotten through, then it would not be because the code can pass after every nested-multi-condition-else-if, in every program say if we used this style. Just till all the conditions happen to keep meeting, a nested-multi-condition-else-if code will work. Meaning this would be just by chance, if ever so happens. So ultimately, even if we happen to solve this fully, we still need to abandon the nested-multi-condition-else-ifs.

Earlier WeaknessForCats had written that else-if is not an entity in C++, and else-if are written together because the spaces don't count. Well that may be true, but this is also true that still it works somewhat like a single operator. You are supposed to put an action after the "else" command, but after "else", "if" is smoothly accepted, and you can place an indefinite number of else-if blocks. And there are no errors. But looks like in a nested else-if, first else-if is the limit for C++, whereas in a straight else-if, it works perfectly with any number of else-ifs.

Thanks

[HolyDoom Witch]

I think "if (condition && condition)" is the only option to fulfill all the conditions in such a code. Plus it is going to work smoothly and remain short too. If you still think it is possible in the style your are saying Rabbit, then you might want to post the code itself. Though I think not.

Thanks

[Rabbit]

Glad you got it working.

Regarding your post #5, I can't say I understand what you're trying to say. It sounds like there's a misunderstanding somewhere in there about the if structure.

[HolyDoom Witch]

I am so sorry I did not test it, and your best answer had to be reverted.

That post got edited; though I have explained more clearly what you did not understand.

Well it suddenly struck me and I tested and there it was, not giving anything.

You might want to edit your post too in accordance with the edits.

Thanks

[Rabbit]

I still can't say I understand everything you're trying to say. But you certainly could use && to combine the conditions but it is not the only way to do so.

The following is pseudo code only to show the logic.

if (x==1) {
   if (y==2) {
   } else if (y==3) {
   }
}

if (x==1 && y==2) {
} else if (x==1 && y==3) {
}

Both code blocks result in the same logic flow.

[HolyDoom Witch]

Okay. Here is the deal.

You test the code in the following way:

Consider that last month was your birthday and today is any date past your birth month. Now input the details in the program, and then see the result.

You do this step, and then you'll know what I am saying.

Thanks

[Rabbit]

Test what? You mean test your code? You can test your own code because I don't know what your code currently looks like.

You should be aware though that you don't account for the days after your birthday in your birth month in your code.

[HolyDoom Witch]

Okay then forget it.

As far as accounting for days after the birthday is concerned, then according to you, if someone is using such a program, and last month was his birthday, then no result would be fine, right? And by the way, why should someone account for days BEFORE his birthday if not after his birthday? Because, whatever days are there AFTER his birthday, are also the days BEFORE his NEXT birthday!!!

To anyone else who comes here, this topic is closed. Coding in such a style can never work unless it is something very simple with less conditions. If it has more conditions, then better to use some other operators instead of the NESTED else-if blocks, like 'if (condition&&condition) action;'. Nested else-ifs just don't work in C++.

Thanks to everyone.

[Rabbit]

As far as accounting for days after the birthday is concerned, then according to you, if someone is using such a program, and last month was his birthday, then no result would be fine, right?

No, that's not what I said at all. My point is the opposite, no result would not be fine so you need to account for it.

And by the way, why should someone account for days BEFORE his birthday if not after his birthday? Because, whatever days are there AFTER his birthday, are also the days BEFORE his NEXT birthday!!!

Again you misunderstand my point. Your code doesn't account for when month is equal to b_month and day is greater than b_day. Which means your result will be incorrect when that scenario is reached.

If it has more conditions, then better to use some other operators instead of the NESTED else-if blocks, like 'if (condition&&condition) action;'. Nested else-ifs just don't work in C++.

The question is not whether or not nested if's work. They work. Whether or not it is recommended is another question. It is recommended not to use nested if structures. But that wasn't your question. Your question was how to get nested if's to work even though in your previous thread it was recommended that you not use them.

[HolyDoom Witch]

No, that's not what I said at all. My point is the opposite, no result would not be fine so you need to account for it.

Then know that this is exactly what is happening when we use your style. You can't say a code is working because most conditions work, and one or two don't.

Again you misunderstand my point. Your code doesn't account for when month is equal to b_month and day is greater than b_day. Which means your result will be incorrect when that scenario is reached.

Why does not my code account for this? Which other scenarios can you think of in the last "else" that remains? So you completely ignored this "else". And that has been your problem throughout.

The question is not whether or not nested if's work. They work. Whether or not it is recommended is another question. It is recommended not to use nested if structures. But that wasn't your question. Your question was how to get nested if's to work even though in your previous thread it was recommended that you not use them.

It is not about RECOMMENDATION. The question was, to SEE if things can work this way FOR THIS PARTICULAR CODE, since this style of nested else-if CANNOT at all work past the first else-if, but since I might be forgetting something. Like I said in my opening post: "Though the point that should be taken here is that it won't work this way, and which is all that should matter." The word "recommendation" can apply only where the option is ALWAYS available. Here, this option can be had only when there are far too less conditions.

And that was already concluded.

Thanks

[donbock]

The title of your post refers to "nested else-ifs" but the code you provided does have any nesting of else-ifs. I assure you that else-ifs do indeed work properly, whether nested or not.

The legs of an else-if cascade are mutually exclusive. No more than one leg will be executed. (If your else-if cascade ends with an else then exactly one leg will be executed.) The following two code snippets are equivalent:

if (A) {
   leg1();
} else if (B) {
   leg2();
} else if (C) {
   leg3();
} else {
   leg4();
}

if (A) {
   leg1();
}
if (!A && B) {
   leg2();
}
if (!A && !B && C) {
   leg3();
}
if (!A && !B && !C) {
   leg4();
}

The order of conditions in the else-if cascade establishes the priorities of the conditions. For example, if A is true then you're taking the first leg regardless of whether B or C are true or false.

The preceding discussion has been general and may not address your specific concern. Let's look at your specific program. You have three conditions:

1. your birthday has not yet occurred this year;
2. your birthday is today;
3. your birthday occurred sometime earlier this year.

These three conditions are mutually exclusive: there is no combination of dates for which more than one condition is true. These three conditions are also complete: there is no combinations of dates for which all of them are false. Because the conditions are complete, we only need to explicitly test two of the three conditions - we can rely on the else clause to catch the third condition.

if (your birthday has not yet occurred this year) {
   cout <<"\nYour age is: " << year - b_year - 1 <<" as of today on " <<day <<"-" <<month <<"-" <<year <<".";
} else if (your birthday is today) {
   cout <<"\nHey... you became " <<year - b_year <<" years old today on " <<day <<"-" <<month <<"-" <<year <<"... Happy Birthday!!";
else {
   // your birthday must have occurred sometime earlier this year
   cout <<"\nYour age is " <<year - b_year <<" as of today on " <<day <<"-" <<month <<"-" <<year <<"."; 
}

All that's left is to express the conditions:

if ((month < b_month) || ((month == b_month) && (day < b_day))) {
   // Your birthday has not yet occurred this year.
   cout <<"\nYour age is: " << year - b_year - 1 <<" as of today on " <<day <<"-" <<month <<"-" <<year <<".";
} else if ((month == b_month) && (day == b_day)) {
   // Your birthday is today.
   cout <<"\nHey... you became " <<year - b_year <<" years old today on " <<day <<"-" <<month <<"-" <<year <<"... Happy Birthday!!";
else {
   // Your birthday must have occurred sometime earlier this year.
   cout <<"\nYour age is " <<year - b_year <<" as of today on " <<day <<"-" <<month <<"-" <<year <<"."; 
}

The fact that these conditions contain || and && is due to the complexity of your conditions, not to any inherent limitation of else-if.

Everything I've said here is consistent with what Rabbit has said.

[Rabbit]

Then know that this is exactly what is happening when we use your style. You can't say a code is working because most conditions work, and one or two don't.

I never said the code is working. The code is not working. That's why you asked your question. I only said the technique can work, if done correctly.

Why does not my code account for this? Which other scenarios can you think of in the last "else" that remains? So you completely ignored this "else". And that has been your problem throughout.

The scenario that is not accounted for is the one I already mentioned. Your code doesn't account for when month is equal to b_month and day is greater than b_day. With the nested if, your else is not reached because it first goes to the month == b_month branch of code. I did account for your else clause. You just misunderstood when that else clause is reached when using nested ifs.

It is not about RECOMMENDATION. The question was, to SEE if things can work this way FOR THIS PARTICULAR CODE, since this style of nested else-if CANNOT at all work past the first else-if, but since I might be forgetting something. Like I said in my opening post: "Though the point that should be taken here is that it won't work this way, and which is all that should matter." The word "recommendation" can apply only where the option is ALWAYS available. Here, this option can be had only when there are far too less conditions.

You're wrong, the option is available, you just have to do it correctly.

I was hoping to guide you to the answer but at this point it may be better to just give you the answer so you can see what I'm talking about. This is the solution using nested ifs.

string name;
int day, month, year, b_day, b_month, b_year;
 
cout <<"Enter your first name: "; 
cin >>name;
 
cout <<"H! " <<name <<", what is the date today? Enter day (1 to 31): "; 
cin >>day;
 
cout <<"Now enter the month (1 to 12): "; 
cin >>month;
 
cout <<"And the year? (4 digits): "; 
cin >>year;
 
cout <<"\nNow input your birth date the same way. Day: "; 
cin >>b_day;
 
cout <<"Month: "; 
cin >>b_month;
 
cout <<"Year: "; 
cin >>b_year;
 
if (month < b_month) {
   cout <<"\nYour age is: " <<year - b_year - 1 <<" as of today on " <<day <<"-" <<month <<"-" <<year <<".";
} else if (month == b_month) {
   if (day < b_day) {
      cout <<"\nYour age is: " <<year - b_year - 1 <<" as of today on " <<day <<"-" <<month <<"-" <<year <<".";
   } else {
      if (day == b_day) cout <<"\nHey... you became " <<year - b_year <<" years old today on " <<day <<"-" <<month <<"-" <<year <<"... Happy Birthday!!";
   }
} else {
   cout <<"\nYour age is " <<year - b_year <<" as of today on " <<day <<"-" <<month <<"-" <<year <<".";
}

[HolyDoom Witch]

Ahem... Passengers, Attention Please:
Since DonBock has written everything in accordance with Rabbit (instead of me), and Rabbit has solved the code, passengers are requested to get down of the Dev-CPP Airlines, especially the latest one, since it is only this airline that does not take their route. Since otherwise, they must have tested their route in their airlines (without which they will never give an official statement releasing their plans), it was the fault of the airlines, which we regret. You may apply for a refund of your valuable money.

We have henceforth also decided to close down this airport too.

Thank you for your co-operation. This thread now ends hereby.

[HolyDoom Witch]

Any closing comments?
***

[Rabbit]

Any closing comments on...? There hasn't been anything else said that pertains to the question.

[HolyDoom Witch]

Well, closing comments on how or why your code doesn't work.
***

[Rabbit]

What do you mean doesn't work? It works fine for the most part. I tested it. The only fix that would be needed is an extra else if in the nested if to account for when the month is the same but the day is greater.

But that is not the crux of the question. The point is the code works fine with nested ifs.

[HolyDoom Witch]

"Most part" = Then it doesn't work. Plus, after a fix for THAT scenario, a fix would be needed for when the month is greater than the birth month.

But I think the main thing that escapes your attention is that the code does not go past the FIRST nested else-if in the first place... as told in the very first post.

Thanks for your replies, but I think the code won't work anyway, and you can see that for yourself.
***

[Rabbit]

Here is the fully working code. The only change I had to make was to add an addition else if in there to account for the situation I mentioned above. And I have tested it and it works.

    int day, month, year, b_day, b_month, b_year; 
 
    cout << "H! " << ", what is the date today? Enter day (1 to 31): ";  
    cin >> day; 
 
    cout << "Now enter the month (1 to 12): ";  
    cin >> month; 
 
    cout << "And the year? (4 digits): ";  
    cin >> year; 
 
    cout << "\nNow input your birth date the same way. Day: ";  
    cin >> b_day; 
 
    cout << "Month: ";  
    cin >> b_month; 
 
    cout << "Year: ";  
    cin >> b_year; 
 
    if (month < b_month) { 
       cout << "\nYour age is: " << year - b_year - 1 << " as of today on " << day << "-" << month <<"-" <<year <<"."; 
    } else if (month == b_month) { 
       if (day < b_day) { 
          cout << "\nYour age is: " << year - b_year - 1 << " as of today on " <<day <<"-" <<month <<"-" <<year <<"."; 
       } else if (day == b_day) {
           cout <<"\nHey... you became " <<year - b_year <<" years old today on " <<day <<"-" <<month <<"-" <<year <<"... Happy Birthday!!"; 
       } else {
           cout <<"\nYour age is " <<year - b_year <<" as of today on " <<day <<"-" <<month <<"-" <<year <<"."; 
       }
    } else { 
       cout <<"\nYour age is " <<year - b_year <<" as of today on " <<day <<"-" <<month <<"-" <<year <<"."; 
    } 
 
    return 0;

[HolyDoom Witch]

I think you nailed it all right, and now I know what I was missing.

And I checked your code rather thoroughly, even adding one more else-if after the braces of the first one with a new condition. The program went on that line all right and printed that sentence too when that condition was fulfilled.

What I was missing was, that now there are TWO elses in the same program, one is in the braces that responds to the "if" which itself is IN the braces. And another one is outside, in the main code which is the FINAL ELSE. If you remember, what I was doing was, putting the final else WITHIN the braces, and then I was not left with a FINAL else to cover the rest of the situations, which of course would occur outside; this did not take my attention then. I had even written up there that all I did was put the final else in the braces (which I edited of course, when I found it was still not working fully). It was then and there, that you could have told me that 'where is the final else'? Then I would know that that "else" now belonged to the braces after it was put there. May be I needed to post the code to make that easy for you. (Otherwise... one of these days just before sleeping, I could suddenly have gotten a fit of idea that an else was missing in that code, after which I would rush to the computer from bed! That's how I remember ignored things!)

Other than that, since I had already given up (and closed this thread a few times), it may have been hard for me to guess that. Like you were saying you wanted to "drive" me to an answer. "Data Structures" is the last lesson I have done till now, and I haven't done enough projects of any of them. And which should be the reason for it.

Well it was a small thing and I ate brains of people around HERE, when what I had to do was eat MY OWN brains around THERE. Sorry about that.

So, thanks to everyone-- like DonBock, who may have even tried to point out my mistake. And thanks especially to Rabbit.

The best answer is yours; looks like no one can take that from you.

And yes, your code does not need the braces inside the first brace-set; there is only one action after each "if". It looks very un-confusing this way.
***

[Rabbit]

Glad you achieved the understanding we were trying to reach. Good luck with the rest of your project.

[HolyDoom Witch]

Thanks.
***
(Project = Studies)