so i am trying to write a program that reads some data in from a text file and performs an operation on that data. the text file is as follows...

611111     5
765676     4
876787     4
987897     2
611111     4

now i want the program to read that and see that 611111 is there twice and will add its corresponding values so 611111 will then have a corresponding value of 9. i did some research and found out a map is probably what i need to do this but thats where i am getting confused. im not exactly sure how to read the data into the map from a text file and then how to pick out if there are any similar numbers in the first column.

im not even sure why i am posting what i have so far since i know it is probably embarressingly wrong (especially since i have been working on this for a couple days now). thank you ahead of time!!!

oh and i am using dev-c++ so i cant use strings

char accountNum[6];
int amount;

map<char,int , ltstr> report;

while (!inLN.eof())                      

    report[accountNum] = amount;
6 Years
Discussion Span
Last Post by firstPerson

>char accountNum[6];
If you're using std::map, there's probably no restriction on using std::string as well. I'd highly recommend avoiding C-style strings because they're just too awkward. While C++ isn't known for it's string handling capabilities, std::string is still a vast improvement.

>map<char,int , ltstr> report;
Assuming std::string: std::map<std::string, int> report; . You don't need to provide a comparator because std::string already supports operator<.

>while (!inLN.eof())
*sigh* I can't believe I'm still seeing this bug. getline returns the stream, and you can test the stream directly to get the state. Not only is is correct, it's SHORTER! No excuses.

>report[accountNum] = amount;
Close. According to your requirements, you want to add all of the amounts for matching account numbers together. It's just as intuitive as one would hope, because std::pair is smart about initializing its members:

std::map<std::string, int> report;
std::string account;

while (std::getline(inLN, account)) {
    int amount;

    inLn>> amount; // Assuming a correct file format

    // Add to whatever was there, even a new addition
    report[account] += amount;

oh and i am using dev-c++ so i cant use strings

You should really consider using something besides dev-c++. Code::Blocks is a common suggestion. You should also know that dev-c++ isn't a language or a standard, so, aside from convenience for the classroom, it has no crucial place in the world of c++ programming.

@Narue std::pair is smart about initializing its members
Hmm...true, but I think you should say std::map. This is a bit confusing for the OP.

Also, I would like to emphasize that it is important to declare amount as an int or other numeric type. If you declare it a string because you split a getline() instead of using the istream >> operator, saying report[account] += amount will give you concatenations of the inputs.

Edited by Reverend Jim: Fixed formatting


Step 1: Declare variables

std::map<long,long> report;
std::pair<long,long> info;
std::ifstream file("data.txt");

Step 2: Read in data

while( file >> info.first >> info.second ){
  / * do stuff*/

Step 3: Apply algorithm

while( file >> info.first >> info.second ){
  std::map<long,long>::iterator itr = report.find( info );
  if(itr == report.end() ){ /* if not found then add it */
  else{  //else there is a match
    /* do logic here if match occurs, I'll leave you to implement this */

Step 4: Give me $100 through paypal

Nice doing business with you.

Edited by firstPerson: n/a

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