https://robark.gitlab.io/c++_classes/index.htmlC++ Classes String, Streams, Vector, MapHugoen-usWed, 26 May 2021 22:40:29 +0000https://robark.gitlab.io/c++_classes/string/index.htmlWed, 12 May 2021 18:16:18 +0000https://robark.gitlab.io/c++_classes/string/index.htmlLesson 6: Functions continued and String introduction Palindrome #include <iostream> using namespace std; bool palin(string word){ string rw(""); //sol #1 for (int x=0; x<word.size();x++) { rw = word[x] + rw; // ex: home= h, oh, moh, emoh } //sol #2 /* for (int x=word.size()-1; x>=0 ;x--) { rw = rw + word[x]; // ex: home= e, em, emo, emoh } */ return (rw==word); //if (rw==word) // return true; //return false; } int main(){ string w; cin >> w; if (palin(w)) { cout<<w<< " is a palindrome"<<endl; } else { cout<<w<< " is NOT a palindrome"<<endl; } return 0; } Strings methods:https://robark.gitlab.io/c++_classes/vector1/index.htmlThu, 13 May 2021 21:46:03 +0000https://robark.gitlab.io/c++_classes/vector1/index.htmlStrings continued and Vectors introduction Replace substring #include <iostream> using namespace std; //this program will replace a substring in a user input string //this one works when the new string has the old string in it int main(){ string s; string ow; string nw; cout << "Enter a sentence: "; getline(cin, s); cout << "Enter a word to delete: "; getline(cin, ow); cout << "Enter another word which replaces the deleted word: "; getline(cin, nw); size_t pos(0); while ( (pos = s.find(ow, pos)) != string::npos ) { s.replace( pos, ow.size(), nw); pos = pos + nw.size(); } cout << s << endl; return 0; } Vector initializationhttps://robark.gitlab.io/c++_classes/vector2/index.htmlFri, 14 May 2021 23:11:03 +0000https://robark.gitlab.io/c++_classes/vector2/index.htmlVector Methods Erasing from a vector properly #include <vector> #include <iostream> using namespace std; void printvec(vector <int> v){ for (unsigned int i = 0; i < v.size(); i++) cout << v[i] << ' '; cout << endl; return; } void setvec(vector <int> &v){ v.clear(); for (int i = 0; i < 10; i++) { v.push_back(i); } } int main() { //create vector vector <int> v; vector <int> a; setvec(v); printvec(v); //remove items from vector CORRECT way (iterating backwards) cout<<"correct"<<endl; // unsigned int seg faults as i-- on last iteration = -1 for (int i = v.size()-1 ; i >= 0; i--) { if (v[i] < 5) { v.erase(v.begin() + i); } } printvec(v); //reset vector setvec(v); //remove items from vector the WRONG way (iterating forwards) cout<<"wrong"<<endl; for (unsigned int i = 0; i < v.size();i++) { if (v[i] < 5) { v.erase(v.begin() + i); } } printvec(v); setvec(v); //alternate method to create new vector with items to keep (not in place) cout<<"correct but not in place"<<endl; for (unsigned int i = 0; i < v.size();i++) { if (v[i] >= 5) { a.push_back(v[i]); } } printvec(a); return 0; } Vector orderhttps://robark.gitlab.io/c++_classes/vector3/index.htmlTue, 18 May 2021 22:59:18 +0000https://robark.gitlab.io/c++_classes/vector3/index.html2D Vectors #include <vector> #include <iostream> using namespace std; //create row vectors and push_back into main vector //alternate method using push_back /* int main() { int c=0; vector< vector<int> > v1; for (int i=0; i<3; i++) { vector<int> v2; for (int j=0; j<4; j++) { v2.push_back(++c); } v1.push_back(v2); } //print 2d vector for(unsigned i=0; i<v1.size(); i++) { for (unsigned j=0; j<v1[i].size(); j++) { cout << v1[i][j] << " "; } cout << endl; } return 0; } */ // alternate method initializing size then using assignment int main() { // initialize size then assign elements int c=0; vector< vector<int> > v1 (3, vector <int> (4)); for(unsigned i=0; i<v1.size(); i++) { for (unsigned j=0; j<v1[i].size(); j++) { v1[i][j]=++c; } } for(unsigned i=0; i<v1.size(); i++) { for (unsigned j=0; j<v1[i].size(); j++) { cout << v1[i][j] << " "; } cout << endl; } return 0; } Sorting rows by row sumhttps://robark.gitlab.io/c++_classes/maps/index.htmlTue, 25 May 2021 21:50:08 +0000https://robark.gitlab.io/c++_classes/maps/index.htmlMaps Note: Map iterators I made a mistake in the video. vector and string use random access iterators. So < is valid BUT map uses bidirectional iterators. unordered_map uses forward iterators. #include <iostream> #include <vector> #include <unordered_map> //c++11 using namespace std; int main(){ // key value unordered_map < string, int > nameage; nameage["bob"] = 23; // add key/value pairs nameage["sarah"]= 21; nameage["bob"] = 5; //overwrite //nameage["bill"] = 8; nameage.erase("sarah"); //three ways to iterate // //1 //map<string,int>::iterator i; //for (i=nameage.begin(); i!=nameage.end(); i++) for (auto i=nameage.begin(); i!=nameage.end(); i++) //cannot use < cout<< i->first << ": " << i->second << endl; // key value //2 //c++11 for (auto x: nameage) cout << x.first<< ": "<< x.second << endl; //3 //c++17 use g++ -std=c++17 for (auto [k, v]: nameage ) cout << k << ": " << v <<endl; //cout<<nameage["bill"]<<endl; //returns value 0 but also adds bill,0 to map //cout<<nameage.at("bill")<<endl; //fails. Does not add default values //does key exist if (nameage.find("bill") != nameage.end()) { cout << nameage["bill"] << endl; } else { cout<< "bill is not a key in the map"<<endl; } return 0; }https://robark.gitlab.io/c++_classes/maps2/index.htmlWed, 26 May 2021 22:40:29 +0000https://robark.gitlab.io/c++_classes/maps2/index.htmlMore on Maps #include <iostream> #include <vector> #include <unordered_map> //c++11 #include <map> using namespace std; int main() { // key value unordered_map < string, int > na; //map < string, int > na; na["bob"] = 23; // add key/value pairs na["sarah"]= 21; na["bob"] = 5; //overwrite na["bill"] = 8; na["adam"]= 200; na["zion"]= 3; na["cathy"]=55; na.erase("sarah"); //three ways to iterate // //1 //map<string,int>::const_iterator i; //for (i=na.begin(); i!=na.end(); i++) for (auto i=na.begin(); i!=na.end(); i++) cout<< i->first << ": " << i->second << endl; // key value cout<<endl; /* //if container is a map (not unordered_map) //we can iterate backwards for (auto i=na.rbegin(); i!=na.rend(); i++) cout<< i->first << ": " << i->second << endl; */ cout<<endl; na["sarah"]=11; //2 //c++11 for (auto x: na) //auto &x and auto const &x { cout << x.first<< ": "<< x.second << endl; if (x.first=="sarah") na["sarah"]=22; } cout<<endl; /* //3 //c++17 for (auto [k, v]: na ) cout << k << ": " << v <<endl; */ //cout<<na["bill"]<<endl; //returns value 0 but also adds bill,0 to map (na["bill]=0) //cout<<na.at("bill")<<endl; //fails //does key bob exist if (na.find("bill") != na.end()) { cout << "found bill "<<na["bill"] << endl; } else { cout<< "bill is not a key in the map"<<endl; } //alternate find //if we need to store iterator location to access pair unordered_map<string, int>::iterator p; //map<string, int>::iterator p; if ((p=na.find("sarah"))!=na.end()) { cout<< "found "<< p->first <<" "<< p->second <<endl; } //second alternate find with easier syntax auto q=na.find("sarah"); if (q != na.end()) { cout<< "found "<< q->first <<" "<< q->second <<endl; } return 0; }