C++ sort array of strings - c++

I am trying to sort an array of strings, but it's not sorting anything.... what am I doing wrong?
string namesS[MAX_NAMES];
int compare (const void * a, const void * b){
return ( *(char*)a - *(char*)b );
}
void sortNames(){
qsort(namesS, MAX_NAMES, sizeof(string), compare);
}

This is C++, not C. Sorting an array of strings is easy.
#include <string>
#include <vector>
#include <algorithm>
std::vector<std::string> stringarray;
std::sort(stringarray.begin(), stringarray.end());

std::qsort is inherited from the standard C library. It will not work.
You need to use std::sort for sorting strings.
Specifically, cast std::string to void* and then to char* is undefined and won't work.

algorithm sort in CPP has the same complexity as qsort:
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
bool compare(string a, string b){
cout << "compare(" << a << "," << b << ")" << endl;
return (a.compare(b) < 0);
}
int main () {
string mystrs[] = {"www","ggg","bbb","ssss","aaa"};
vector<string> myvector (mystrs, mystrs + 5);
vector<string>::iterator it;
sort (myvector.begin(), myvector.end(), compare);
cout << "vector contains:";
for (it=myvector.begin(); it!=myvector.end(); ++it)
cout << " " << *it;
cout << endl;
return 0;
}

You can use boost::sort, like this:
#include <vector>
#include <boost/range/algorithm.hpp>
std::vector<std::string> stringarray;
boost::sort(stringarray);
If you want use find use boost::find, like this:
std::string findme;
auto offset = boost::find(stringarray, findme) - stringarray.begin()
See 2 useful functions (m_stringarray should be member of ClassA):
const size_t ClassA::GetIdByName(std::string name) const
{
return (boost::find(this->m_stringarray, name) - this->m_stringarray.begin());
}
const std::string ClassA::GetNameById(size_t id) const
{
return this->m_stringarray[id];
}

As many here have stated, you could use std::sort to sort, but what is going to happen when you, for instance, want to sort from z-a? This code may be useful
bool cmp(string a, string b)
{
if(a.compare(b) > 0)
return true;
else
return false;
}
int main()
{
string words[] = {"this", "a", "test", "is"};
int length = sizeof(words) / sizeof(string);
sort(words, words + length, cmp);
for(int i = 0; i < length; i++)
cout << words[i] << " ";
cout << endl;
// output will be: this test is a
}
If you want to reverse the order of sorting just modify the sign in the cmp function.

Here is C++ another way to sort array of string without using <vector>.
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string WordArray[] = {"AA","DD","CC","BB","ZZ","NN"};
sort(begin(WordArray), end(WordArray)); /*Sort the Array*/
for(auto& Word: WordArray){
cout<<Word<<endl; /*Print Every String Element*/
}
return 0;
}

Related

How can I concatenate the elements of a vector of integers to a string in C++?

I've been trying to put every single element of a vector of integers into a string. I want to achieve this by type casting the integers into strings, after that I cocatenate those "small strings" into a single big string, which is going to represent all the elements of that specific vector.
This may look silly, but is really useful if you want to make a function that returns a vector like-a-thing, or etc.
The only problem is that I'm getting an error on line 13, which says :
error: no matching function for call to ‘std::__cxx11::basic_string<char>::basic_string(int&)’
13 | myString += (string) myVector[i];
| ^
and I don't have the slightest idea on why this is happening. My code follows below :
#include <iostream>
#include <vector>
using namespace std;
int main()
{
int myVector[5] = {1,2,3,4,5};
string myString = "";
for (int i =0; i < 5; i++)
{
myString += (string) myVector[i];
myString += "\n";
}
cout << myString << endl;
any help will be much appreciated.
You can use std::to_string to convert an int to a std::string.
Change this line:
myString += (string) myVector[i];
To:
myString += std::to_string(myVector[i]);
Note: concatenating strings like that might not be so efficient due to temporary strings being created and destroyed (although it is likely that small strings optimization will kick in, so no additional heap allocations will take place).
As #Someprogrammerdude commented, you can consider to use std::ostringstream.
Side notes:
You are missing #include <string>.
Why is "using namespace std;" considered bad practice?.
You can use the fmt library:
fmt::join will accept a range, in your case a vector of ints, and join its contents with a given separator (e.g. an empty string if you just want all of the elements together).
fmt::format will create a string with a given format, in this case just the contents of the joined vector.
Demo
#include <fmt/ranges.h>
int main() {
int myVector[5] = {1,2,3,4,5};
auto myString = fmt::format("{}", fmt::join(myVector, ""));
fmt::print("{}\n", myString);
}
// Outputs: 12345
Or, simpler, if you don't need the string:
int main() {
int myVector[5] = {1,2,3,4,5};
fmt::print("{}\n", fmt::join(myVector, ""));
}
The error you are getting is saying that the compiler cannot find a std::__cxx11::basic_string<char>::basic_string(int&) function, i.e., a std::string constructor accepting an int&.
You can use std::stringstream
#include <iostream>
#include <string>
#include <sstream>
int main()
{
int myVector[5] = {1,2,3,4,5};
std::string myString;
std::stringstream sstream;
for (auto i : myVector)
sstream << i;
sstream >> myString;
std::cout << myString;
}
Link.
I'll add my own solution, as laid out in my comment:
#include <iostream>
#include <iterator>
#include <algorithm>
#include <vector>
int main()
{
std::vector myvector = { 1, 2, 3, 4, 5 };
std::copy(std::begin(myvector), std::end(myvector),
std::ostream_iterator<int>(std::cout, "\n"));
}
Overload the output stream operator, and then you have something reusable for a lot of scenarios.
Based on the feedback below overloading is not the best answer, another approach here : https://www.onlinegdb.com/zDUjVbSTp
#include <vector>
#include <iostream>
#include <string>
#include <sstream>
// Overloading operator<< will have many benefits.
// you can use it to output an array to std::cout directly
// or you can write it to a file or stringstream
std::ostream& operator<<(std::ostream& os, const std::vector<int>& values)
{
os << "[";
bool comma = false;
for (const auto& value : values)
{
if (comma) os << ", ";
os << value;
comma = true;
}
os << "]";
return os;
}
int main()
{
std::vector<int> values{ 1,2,3,4,5 };
// write directly to std::cout
std::cout << "direct : " << values << "\n";
// adding array to a string
std::ostringstream os;
std::string string{ "output = " };
os << values;
string += os.str();
std::cout << string << "\n";
return 0;
}
You can use for_each algorithm as well to do the concatenation.
#include <iostream>
#include <algorithm>
int main()
{
std::vector<int> v{1, 2, 3, 4, 5, 6};
std::string all;
std::for_each(v.begin(), v.end(), [&, del=""](const int &e) {
all += std::to_string(e) + (&e == &v.back() ? "" : del);
});
std::cout << all << std::endl;
}
output:
123456
If you want to add a delimiter in between, just change the del value in lambda capture.
std::for_each(v.begin(), v.end(), [&, del="-"](const int &e) {
all += std::to_string(e) + (&e == &v.back() ? "" : del);
});
Output:
1-2-3-4-5-6

unordered_set count function returns wrong value

Why does set.count('a') output 1 when there are 3 a's?
Program:
bool isAnagram(string s, string t) {
unordered_set<char> set;
for(int i=0; i<s.size(); i++){
set.insert(s[i]);
}
cout << endl << set.count('a') << endl;
return false;
}
Input:
s = 'anagram'
Output:
1
There's only one a in the set. If you want multiple as you need to use a multiset.
Example:
#include <iostream>
#include <set>
#include <string>
size_t count_char(const std::string& s, char ch) {
// fill the set directly using the strings begin and end iterators
std::multiset<char> set(s.begin(), s.end());
return set.count(ch);
}
int main() {
std::cout << count_char("anagram", 'a') << '\n';
}
Output:
3
You have to specify the range in count function :
count (InputIterator first, InputIterator last, const T& val)
Example:
#include <iostream>
#include <algorithm>
using namespace std;
int main(){
string s= "anagram";
cout << count(s.begin(), s.end(), 'a') << endl;
return 0;
}
Output:
3

How can I parse a vector to a bool in C++?

I'm trying to write a program that first checks if a name is in a vector and if not then adds it to the vector. My code seems to have difficulties with parsing, at least that's what I get out of it. I tried changing the string to a char but it did not help me much.
#include <iostream>
#include <vector>
#include <string>
bool isinVector(std::string uElement, std::vector<std::string> uArray)
{
for (unsigned int i = 0; i <= sizeof(uArray); i++) {
if (uArray[i] == uElement) {
return true;
}
else {
return false;
}
}
}
int main()
{
bool trigger = false;
while (!trigger) {
std::vector<std::string> names;
names.push_back("Bart");
std::string newName;
getline(std::cin, newName);
if (isinVector(newName, names))
{
std::cout << "true" << std::endl;
trigger = true;
}
else
{
std::cout << "false" << std::endl;
names.push_back(newName);
for (int i = 0; i <= sizeof(names); i++) {
std::cout << names[i] << std::endl;
}
}
}
}
I made some adjustments to your code, removing your isinVector function and using a lambda inside the main function instead. In the future please provide a concise question and example.
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using std::vector;
using std::string;
using std::cout;
using std::cin;
using std::endl;
using std::find_if;
int main(){
bool trigger = false;
while (!trigger) {
vector<string> names;
names.push_back("Bart");
string newName;
getline(cin, newName);
if(find_if(names.begin(), names.end(), [newName] (const string& name){
return !name.compare(newName);
}) != names.end()){
cout << "true" << endl;
trigger = true;
}
else{
cout << "false" << endl;
names.push_back(newName);
for (size_t i = 0; i < names.size(); i++) {
cout << names.at(i) << endl;
}
}
}
return 0;
}
The code uses std::find_if to check if the element exists in the vector. If std::find_f does not return the iterator to uArray.end() Then the element exists. Also your for loop used sizeof which is incorrect, use the vector.size method. And you were looping until <= , it should be < uArray.size() And it's safer to access elements in the vector through the .at method rather than an index [] since the .at will throw an out_of_range exception.
Among the things wrong in the updated post.
Improper use of sizeof
Reinventing a standard algorithm
Lack of error checking
Consider the tasks you're trying to accomplish. You want to:
Initialize a starting vector containing the name Bart
Continuously read new names. For each new name read:
a. Check to see if it is already in the vector.
if it is present terminate the read loop
else add it to the vector, and print the entire vector
This sequence of operations can be accomplished with stepwise refinement.
Step 1. Read names
First, you need to be able to continuously read names:
#include <iostream>
#include <string>
int main()
{
std::string name;
while (std::getline(std::cin, name))
std::cout << name << '\n';
}
Simple enough. Running this will echo any strings you type, one at a time, separated by newlines.
Step 2. Accumulate names in a vector
Next, we need to add a vector to hold the strings we're reading, with an initial population of the name "Bart". For this pass we'll be just putting every string we read into the vector
#include <iostream>
#include <vector>
#include <string>
int main()
{
std::vector<std::string> names = { "Bart" };
std::string name;
while (std::getline(std::cin, name))
{
names.emplace_back(name);
for (auto const& s : names)
std::cout << s << ' ';
std::cout.put('\n');
}
}
In addition to what was done prior, we're now accumulating strings in the vector, including duplicates, and reporting the vector content after each name read. This gets us closer to our stated goal.
Step 3: Conditional loop exit based on duplicate detection
Now we need to check for duplicates, and terminate the loop once it happens. We can do this using std::find. The final code is below:
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
int main()
{
std::vector<std::string> names = { "Bart" };
std::string name;
while (std::getline(std::cin, name))
{
if (std::find(names.begin(), names.end(), name) != names.end())
break;
names.emplace_back(name);
for (auto const& s : names)
std::cout << s << ' ';
std::cout.put('\n');
}
}
That's it. This is a simple task, but it lends itself nicely to an example of how you break a multi-part task down to manageable objectives , then build it in pieces.
Hope you found it useful.
Now my code looks like this:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
bool isinVector (std::string uElement, std::vector<std::string> uArray) {
bool invector = false;
std::vector<std::string>::iterator it = std::find(uArray.begin(),
uArray.end(),uElement);
if(it != uArray.end()){
invector = true;
}
return invector;
}
int main(){
bool trigger = false;
std::string name;
std::vector<std::string> names = { "Bart" };
while (std::getline(std::cin, name)){
if (isinVector(name, names)) {
std::cout << "true" << std::endl;
break;
}
else
{
std::cout << "false" << std::endl;
names.emplace_back(name);
}
}
return 0;
}
and it works, thanks a lot guys!

add each int in a vector<int> to a string

for (vector<int>::const_iterator i = vec.begin(); i != vec.end(); ++i)
{
int number = *i;
char* c;
itoa(number, c, 10);
result += c;
}
std::cout << result << std::endl;
I'm trying to convert each int in "vec" to a char and adding it to a string but I just get a compiler error. what am I doing wrong?
You can use the std::to_string available in C++11:
#include <iostream>
#include <vector>
#include <string>
int main()
{
std::vector<int> vec;
for (int i = 0; i < 100; i++)
{
vec.push_back(i);
}
std::string result;
for (std::vector<int>::const_iterator i = vec.begin(); i != vec.end(); ++i)
{
result += std::to_string(*i);
}
std::cout << result << std::endl;
}
Combining sounds like a job for std::accumulate.
#include <iostream>
#include <numeric>
#include <string>
#include <vector>
auto main() -> int
{
const std::vector<int> vec{ 1, 2, 3 };
const std::string result = std::accumulate(vec.begin(), vec.end(), std::string(),
[](const std::string& s, const int value)
{
return s + std::to_string(value);
});
std::cout << result << std::endl;
}
There's an error in your code:
You call itoa() with a non-initialized char pointer. That's bad, because itoa() needs a valid buffer! Besides, itoa() is not part of the c++ standard.
Better do leave char* behind and do it with more modern C++ features, especially std::stringstream, which is a string builder, which is powerful in conversion (and also often faster than the string += operator). It builds a string by pushing elements to it with the << operator (these can be string literals, strings, numbers of all kinds), it can be extended via external operators for own data types, and it also has a lot of formatting options (e.g. number of digits, hex etc), and returns its built string with the method str().
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
int main()
{
std::vector<int> vec;
for (int i = 0;i<100;i++)
vec.push_back(i);
std::stringstream ss;
for (auto& number : vec)
ss << number;
std::cout << ss.str() << std::endl;
}

Removing all the characters (a-z, A-Z) from a string in C++

Here's my code:
#include <iostream>
using namespace std;
string moveString(string t, int index)
{
for (int i=index; t[i]!=NULL;i++)
{
t[i]=t[i+1];
}
return t;
}
string delChars(string t)
{
for (int i=0; t[i]!=NULL; i++)
{
if (t[i]>'a' && t[i]<'z')
{
moveString(t, i);
}
else if (t[i]>'A' && t[i]<'Z')
{
moveString(t, i);
}
}
return t;
}
int main()
{
int numberOfSpaces;
string t;
cout << "Text some word: "; cin>>t;
cout<<delChars(t);
return 0;
}
First function moveString should (in theory) take down every single character from a string by 1 index down (starting from given index) - to remove 1 character. The rest is pretty obvious. But:
Input: abc123def
Output: abc123def
What am I doing wrong?
And a additional mini-question: Acutally, what's the best way to "delete" an element from an array? (array of ints, chars, etc.)
Logic Stuff is right but his answer is not enough. You shouldn't increase i after move. Since the i.th character is removed and i points to the next character now.
string delChars(string t)
{
for (int i=0; t[i]!=NULL; )
{
if (t[i]>'a' && t[i]<'z')
{
t = moveString(t, i);
}
else if (t[i]>'A' && t[i]<'Z')
{
t = moveString(t, i);
}
else
i++;
}
return t;
}
moveString takes t by value and you're not assigning its return value, so it doesn't change t in delChars. So, make sure the next thing you learn are references.
Apart from that, I don't know what to tell about t[i] != NULL (if it is undefined behavior or not), but we have std::string::size to get the length of std::string, e.g. i < t.size(). And if you havet[i + 1], the condition should then be i + 1 < t.size().
Whatever, don't play with it like with char arrays, leaving the string with previous size. You can pop_back the last (duplicate) character after shifting the characters.
It's worth mentioning that it can be done in one line of idiomatic C++ algorithms, but you want to get your code working...
What am I doing wrong?
Not using standard algorithms
Actually, what's the best way to "delete" an element from array? (array of ints, chars, etc.)
By using the standard remove-erase idiom:
#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cstring>
int main()
{
using namespace std;
auto s = "!the 54 quick brown foxes jump over the 21 dogs."s;
cout << "before: " << quoted(s) << endl;
s.erase(std::remove_if(s.begin(),
s.end(),
[](auto c) { return std::isalpha(c); }),
s.end());
cout << "after: " << quoted(s) << endl;
return 0;
}
expected output:
before: "!the 54 quick brown foxes jump over the 21 dogs."
after: "! 54 21 ."
I'm not allowed to use standard algorithms
Then keep it simple:
#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cstring>
std::string remove_letters(const std::string& input)
{
std::string result;
result.reserve(input.size());
for (auto c : input) {
if (!std::isalpha(c)) {
result.push_back(c);
}
}
return result;
}
int main()
{
using namespace std;
auto s = "!the 54 quick brown foxes jump over the 21 dogs."s;
cout << "before: " << quoted(s) << endl;
auto s2 = remove_letters(s);
cout << "after: " << quoted(s2) << endl;
return 0;
}