My code is not able to pass one of the test cases because it is producing a wrong value, which I can't find why. What could be the problem in my code?

Question

Question - Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Unfortunately, not all numbers are lucky. Petya calls a number nearly lucky if the number of lucky digits in it is a lucky number. He wonders whether number n is a nearly lucky number.

Input - The only line contains an integer n (1 ≤ n ≤ 1018).

Please do not use the %lld specificator to read or write 64-bit numbers in С++. It is preferred to use the cin, cout streams or the %I64d specificator.

Output - Print on the single line "YES" if n is a nearly lucky number. Otherwise, print "NO" (without the quotes).

Question Link - https://codeforces.com/problemset/problem/110/A

My code -

int main(){
    int a,b=0;
    cin >> a;
    string x = to_string(a);
    for(int i=0;i<x.length();i++){
        if(x[i]=='4' || x[i]=='7'){
            b++;
        }
    }
    cout << b;
    if(b==4 || b==7){
        cout << "YES";
    }else{cout << "NO";}
}

It is passing numerous test cases but there is one which it fails. When the integer is 4744000695826 , the value of my B is 5 therefore the output is NO. I am not understanding why is the value of B = 5, whereas it should be equal to 4 and even my code seems to be working that way. What could be the possible problems?

@ProgrammerGuy `std::cout << std::numeric_limits::max() << std::endl;` – Overflowing or underflowing these boundaries will invoke undefined-behavior. — Rohan Bari, Mar 21 '21 at 04:28
Why read it as an int then convert it to a string and never use the int again? Just read it as a string to begin with. — Retired Ninja, Mar 21 '21 at 04:37
When I asked the rotrical question I had forgotten how it felt to be a newcommer. Good thing I got to upvote before Community shut it down. — Ted Lyngmo, Mar 21 '21 at 04:46
"_rotrical_" should have been "_rhetorical_" - even though "rotrical" is a bit more amusing — Ted Lyngmo, Mar 21 '21 at 09:35

score 2 · Answer 1 · answered Mar 21 '21 at 04:32

2

Integers have certain limits, and exceeding the limits can cause undefined behavior, so instead of int, long long will be used. Updated code -

int main(){
    long long a,b=0;
    cin >> a;
    string x = to_string(a);
    for(int i=0;i<x.length();i++){
        if(x[i]=='4' || x[i]=='7'){
            b++;
        }
    }
    cout << b;
    if(b==4 || b==7){
        cout << "YES";
    }else{cout << "NO";}
}

answered Mar 21 '21 at 04:32

ProgrammerGuy

157
9

1

Quick study! Have an upvote! – Ted Lyngmo Mar 21 '21 at 04:33
1

**ProTip!** You can use `!cin.good()` to verify if the value assignment was successful. – Rohan Bari Mar 21 '21 at 04:35
What @RohanBari mentioned is good. You have table of [state combinations](https://en.cppreference.com/w/cpp/io/ios_base/iostate) you can look at (it's down at the bottom on that page). – Ted Lyngmo Mar 21 '21 at 09:46

My code is not able to pass one of the test cases because it is producing a wrong value, which I can't find why. What could be the problem in my code?

1 Answers1