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C++ if statement help

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C++ if statement help

 
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  #1
Sep 15th, 2005
Hello, noob here. I just started taking a C++ class this semester and I've been understanding everything so far, but I'm sorta confused on the nested if statements. My homework is to have the user enter a number and it'll show the roman numeral. However whenever someone enters an invalid number it still executes both statements.

C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. #include <string> 
  3. using namespace std;
  4.  
  5. // main()
  6. int main()
  7. {
  8.  
  9.    int number;          
  10.    string numeral;  
  11.  
  12. 	cout << "Please enter a number between 1 and 10 ";
  13. 	cin >> number;
  14. {
  15. 		if(number == 1)
  16. 			numeral = "I";
  17. 		else if(number == 2)
  18. 			numeral = "II";
  19. 		else if(number == 3)
  20. 			numeral = "III";
  21. 		else if(number == 4)
  22. 			numeral = "IV";
  23. 		else if(number == 5)
  24. 			numeral = "V";
  25. 		else if(number == 6)
  26. 			numeral = "VI";
  27. 		else if(number == 7)
  28. 			numeral = "VII";
  29. 		else if(number == 8)
  30. 			numeral = "VIII";
  31. 		else if(number == 9)
  32. 			numeral = "IX";
  33.                           else if(number == 10)
  34.                           numeral = "X";
  35. else cout << "The number entered was not between 1 and 10";
  36. 	}	
  37. cout << "The Roman numeral for the number " << number << " is " << numeral;
  38.     cin.ignore();
  39.     cin.get();
<< moderator edit: added [code][/code] tags >>


For some reason it's always printing out the last cout. Also everything is lined up in the program i just had it moved in the post so it'd fit.
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Re: C++ if statement help

 
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  #2
Sep 15th, 2005
C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. #include <string> 
  3. using namespace std;
  4.  
  5. // main()
  6. int main()
  7. {
  8. 	int number;          
  9. 	string numeral;  
  10.  
  11. 	cout << "Please enter a number between 1 and 10 ";
  12. 	cin >> number;
  13.  
  14. 	{
  15. 		if(number == 1)
  16. 			numeral = "I";
  17. 		else if(number == 2)
  18. 			numeral = "II";
  19. 		else if(number == 3)
  20. 			numeral = "III";
  21. 		else if(number == 4)
  22. 			numeral = "IV";
  23. 		else if(number == 5)
  24. 			numeral = "V";
  25. 		else if(number == 6)
  26. 			numeral = "VI";
  27. 		else if(number == 7)
  28. 			numeral = "VII";
  29. 		else if(number == 8)
  30. 			numeral = "VIII";
  31. 		else if(number == 9)
  32. 			numeral = "IX";
  33. 		else if(number == 10)
  34. 			numeral = "X";
  35. 		else cout << "The number entered was not between 1 and 10";
  36. 	}
  37.  
  38. 	cout << "The Roman numeral for the number " << number << " is " << numeral;
  39.  
  40. 	cin.ignore();
  41. 	cin.get();
I cleaned up your code a bit. You will notice that your set of curly braces surrounding the if statements isn't doing anything. You want one of two messages printed, but you have a series of eleven conditions that can be met. Only one of the conditions prints a message. Irregardless of which condition is met, the final message is printed. Thus, if the else statement is used, two messages will be printed.

You have two options:
  • Print a message for each condition
    C++ Syntax (Toggle Plain Text) 
    1. if(number == 1)
    2. {
    3. 	cout << "The Roman Numeral for the number 1 is I\n";
    4. }
    5. else if(number == 2)
    6. {
    7. 	cout << "The Roman Numeral for the number 2 is II\n";
    8. }
    9. // etc
  • Divide the logic into two different sets: valid number and invalid number
    C++ Syntax (Toggle Plain Text) 
    1. if((number < 1) && (number > 10))
    2. {
    3. 	cout << "The number entered was not between 1 and 10\n";
    4. }
    5. else
    6. {
    7. 	if(number == 1)
    8. 		numeral = "I";
    9. 	else if(number == 2)
    10. 		numeral = "II";
    11. 	//etc
    12.  
    13. 	cout << "The Roman numeral for the number " << number << " is " << numeral;
    14. }
The second solution is the better solution.

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Re: C++ if statement help

 
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  #3
Sep 15th, 2005
Eventually, you'll be able to do the same thing with a switch statement, but understanding how and when to use nested ifs is important.
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Re: C++ if statement help

 
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  #4
Sep 15th, 2005
Thanks a lot that helped out a ton. Also I was wondering if anyone knows of a good book or something that'll help out with C++ I'm trying to teach my girlfriend (we're taking the same class) but she's still confused about everything.
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Re: C++ if statement help

 
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  #5
Sep 15th, 2005
Isn't there a topic at the top of the forum about good C/C++ books?

Whatever you do, avoid anything written by Herb Schlidt. (Thanks again, Dave!)
He's easy to read, but chock full o' errors.
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Re: C++ if statement help

 
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  #6
Sep 15th, 2005
yeah i saw that, but I was just wondering if anyone knows of any other ones that might be helpful too, or a video or something. But thanks alot everyone.
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Re: C++ if statement help

 
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  #7
Sep 16th, 2005
I found these 2 books very helpful
Thinking in c++ volumes 1 and 2
You find links to download them at www.BruceEckel.com
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