(C++) How to detect decimal points?

This is a discussion on (C++) How to detect decimal points? within the C++ Programming forums, part of the General Programming Boards category; Using an If statement how could I go about detecting a decimal enter by the user? Basically I am writing ...

  1. #1
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    (C++) How to detect decimal points?

    Using an If statement how could I go about detecting a decimal enter by the user?


    Basically I am writing a program that prompts the user to enter the month and date and I want to be able to send a warning message if a decimal point is used.

  2. #2
    Registered User Gnoober's Avatar
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    Correct me if I'm wrong because I am new to C++, but if you declare and integer type, any number assigned to the variable will automatically be truncated into an integer.
    Example:
    Code:
    #include <iostream>
    using namespace std;
    
    int main{
        int a;
        cout<<"Enter a decimal number: ";
        cin>>a;
        cout<<a;
    
        return 0;
    }
    If you input 3.14159, it should output 3, but I'd be more confident if a more experience coder agreed with me
    - Grady (:

  3. #3
    Guest Sebastiani's Avatar
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    That's right. But I think he's referring to character array input. In that case:

    Code:
    loop infinite:
    un-set a flag;
    get input;
    loop < length:
    if string[index] is a '.' {
      - tell user that you have an annoying 
     non-user-friendly program much like DOS which doesn't
     intelligently handle these things;
      - set a flag;
     } 
    :end loop
    if flag isn't set {
      jump out of loop;
     }
    :end infinite



    ITSA
    Socket Library!

  4. #4
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    Code:
    #include <iostream.h>
    int main()
    {
    
         int month, day;
    
    cout << "Enter a month (use a 1 for Jan, ect.): ";
    cin >> month;
    cout << "Enter a day of the month: ";
    cin >> day;
    
    if (month < 1 || month > 12 || month == '.' )
      cout << "An incorrect month was entered" << endl;
    else
      cout << "The month number is " << month << endl;
    
    if (day < 1 || day > 31 || day == '.')
      cout << "An incorrect date was entered" << endl;
    else
      cout << "The date number is " << day << endl;
    
    return 0;
    
    }
    Ok this is how I figured it out.


    Intresting code Sebastiani. I have gotten into loops yets. My fav part is "non-user-friendly program much like DOS which doesn't intelligently handle these things;
    "

  5. #5
    Just a Member ammar's Avatar
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    Maybe you can use this...
    if you read an integer
    Code:
    int x;
    cin >> x;
    if ( cin.good() )     //this is to check if the value entered in an integer ( has no decimals )
    Is that what you mean

  6. #6
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    you could use

    getline(cin,string,'.')

    and the read would end at the decimal

    then you could check the string length and use an if statement if i's too short.
    --Cid666

  7. #7
    I lurk
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    Here's a mighty easy way to check if a variable has any decimal points...

    Code:
    #include <cmath>
    
    // ...
    
    if (std::floor(choice) == choice)
    {
    	// No decimal
    } else {
    	// Decimal
    }
    As for "if (month < 1 || month > 12 || month == '.' )", it's pretty pointless to test for '.', as you'll fail on one of the other tests if '.' is entered anyway.

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