The code is equivalent to:
weight[65] = 500.98;
weight[80] = 455.49;
Which of course only works if the vector holds at least 81 elements.
sepp2k
2010-08-14 13:45:55
+5
A:
Thanks, I have corrected it
ladyfafa
2010-08-14 13:48:23
@sepp2k: It looks like it holds 128 so we should be fine.
Martin York
2010-08-14 15:53:32
+5
A:
You should not.
Use std::map for that purpose
For example
std::map<char,double> Weight;
Weight.insert(std::make_pair('A',500.98)); //include <algorithm>
Weight.insert(std::make_pair('P',455.49));
std::cout<< Weight['A']; //prints 500.98
You can also iterate over the map using std::map<char,double>::iterator
For example
std::map<char,double>::iterator i = Weight.begin();
for(; i != Weight.end(); ++i)
std::cout << "Weight[" << i->first << "] : " << i->second << std::endl;
/*prints
Weight['A'] : 500.98
Weight['P'] : 455.49
*/
Prasoon Saurav
2010-08-14 13:46:27
A character is an integer type so is a valid index into an array (or vector). By changing from a vector to map you are changing the access charastics from O(1) to O(log(n)) not a good trade off.
Martin York
2010-08-14 15:48:18
@Martin : I never said it was not a valid index. I just said that he/she should not use that because that would indeed be more confusing. Using a `std::map` is cleaner. `you are changing the access charastics from O(1) to O(log(n)) not a good trade off`. That would have a significant impact if n is a very large value. For a small value of `n` and looking at the cleaner syntax of `std::map` I would recommend it. This was not at all a good reason to downvote. You should downvote when the answer is completely wrong or misleading.
Prasoon Saurav
2010-08-14 15:50:40
@Prasoon Saurav: I do consider the answer wrong. And I disagree that using std::map is cleaner to me is seems to complicate things (and complicating a simple concept is a bad trade off). But thanks on the tutorial on how and why to vote.
Martin York
2010-08-14 16:00:33
@Martin York : You make me laugh. What does your definition of `wrong` say? `But thanks on the tutorial on how and why to vote`. My pleasure.
Prasoon Saurav
2010-08-14 16:04:19
Martin York
2010-08-14 16:24:14
@Martin : So the community is with you. Kudos! :) BTW no offense meant :)
Prasoon Saurav
2010-08-15 03:07:02
+6
A:
Character literals (like 'A' and 'P') can be automatically converted to integers using their ASCII values. So 'A' is 65, 'B' is 66, etc.
So your code is the same as:
weight[65] = 500.98;
weight[80] = 455.49;
The reason you'd ever want to do this is if the weight array has something to do with characters. If it does, then assigning weights to a character literal makes the code more readable than assigning to an integer. But it's just for "documentation", the compiler sees it as integers either way.
SoapBox
2010-08-14 13:46:54
@SoapBox: Okay, I see, these character literals can be converted to ints
ladyfafa
2010-08-14 13:50:24
For counting the number of occurences of ASCII characters (for example prior to compute a Huffman coding tree) it's okay, however changing the character set to hold more than the lower ASCII would invalidate this scheme.
Matthieu M.
2010-08-14 16:34:05
A:
If you want this, you could use a std::map<char, double>. Technically, it would also be possible using a std::vector<double>, but there'd be all sorts of integral conversions from characters to integers and the program would just be confusing.
DeadMG
2010-08-14 13:47:40
+1
A:
So I understand that char literals are turned into Integers. Does C++ support extended ASCII table ?? For example if I had a
char * blah = 'z'+'z';
what would happen ??? eg.
'z' = 122 in ASCII
therefore
'z'+'z' = 244 ?? or ??
Muggen
2010-08-14 13:58:11
Try :)char* blah = 'z';won't compile, as you are mixing a char ('z') and a char* (blah).If you use char blah: It depends whether a "char" is a "signed char" or "unsigned char" for your compiler. For mine, it is signed and above math results in -12.
Frank
2010-08-14 16:19:13