Cleaning a string of punctuation in C++

Ok so before I even ask my question I want to make one thing clear. I am currently a student at NIU for Computer Science and this does relate to one of my assignments for a class there. So if anyone has a problem read no further and just go on about your business. Now for anyone who is willing to help heres the situation. For my current assignment we have to read a file that is just a block of text. For each word in the file we are to clear any punctuation in the word (ex : "can't" would end up as "can" and "that--to" would end up as "that" obviously with out the quotes, quotes were used just to specify what the example was). The problem I've run into is that I can clean the string fine and then insert it into the map that we are using but for some reason with the code I have written it is allowing an empty string to be inserted into the map. Now I've tried everything that I can come up with to stop this from happening and the only thing I've come up with is to use the erase method within the map structure itself. So what I am looking for is two things, any suggestions about how I could a) fix this with out simply just erasing it and b) any improvements that I could make on the code I already have written. Here are the functions I have written to read in from the file and then the one that cleans it. Note: the function that reads in from the file calls the clean_entry function to get rid of punctuation before anything is inserted into the map. Edit: Thank you Chris. Numbers are allowed :). If anyone has any improvements to the code I've written or any criticisms of something I did I'll listen. At school we really don't get feed back on the correct, proper, or most efficient way to do things. ``` int get_words(map<string, int>& mapz) { int cnt = 0; //set out counter to zero map<string, int>::const_iterator mapzIter; ifstream input; //declare instream input.open( "prog2.d" ); //open instream assert( input ); //assure it is open string s; //temp strings to read into string not_s; input >> s; while(!input.eof()) //read in until EOF { not_s = ""; clean_entry(s, not_s); if((int)not_s.length() == 0) { input >> s; clean_entry(s, not_s); } mapz[not_s]++; //increment occurence input >>s; } input.close(); //close instream for(mapzIter = mapz.begin(); mapzIter != mapz.end(); mapzIter++) cnt = cnt + mapzIter->second; return cnt; //return number of words in instream } void clean_entry(const string& non_clean, string& clean) { int i, j, begin, end; for(i = 0; isalnum(non_clean[i]) == 0 && non_clean[i] != '\0'; i++); begin = i; if(begin ==(int)non_clean.length()) return; for(j = begin; isalnum(non_clean[j]) != 0 && non_clean[j] != '\0'; j++); end = j; clean = non_clean.substr(begin, (end-begin)); for(i = 0; i < (int)clean.size(); i++) clean[i] = tolower(clean[i]); } ```