I am running a C++ program to sort strings as numbers.
I am saving strings in a char array vector but want to sort numbers as numbers so I am converting number strings into long doubles by calling "tonum()" then converting them back to strings when I am done by calling "tostring()". I am calling "numstr()" strictly for readability and debugging. I convert numbers 0 through 7 and the 6th number across for each value changes every time I run it. In my actual program, the first 5 numbers also seem to change. How do I get consistent results for a long double so that I can properly sort long doubles in char arrays?
#include<iostream>
std::string::size_type sz;
//___________________________________________________
std::string tonum(std::string str)
{
const int len = sizeof(long double);
std::string out = "0000000000000000";
union
{
long double dbl;
char array[len];
};
try
{
dbl = stold(str);
}
catch(std::exception &err)
{
dbl = 0;
}
for (int i = 0; i < len; i++)
{
std::cout << (int)array[i] << "\n";
out[len-i-1] = array[i];
}
return(out);
}
//___________________________________________________
std::string fromnum(std::string str)
{
const int len = sizeof(long double);
std::string out = "";
union
{
long double dbl;
char array[len];
};
for (int i = 0; i < len; i++)
{
array[len-i-1] = str[i];
}
out = std::to_string(dbl);
return(out);
}
//_____________________________________________________
std::string numstr(std::string str)
{
std::string out = fromnum(str) + ":";
for (int i = 0; i < str.length(); i++)
{
std::string look = std::to_string(str[i]);
int lookint = stold(look,&sz);
if (lookint < 0) lookint += 256;
std::string look2 = std::to_string(lookint);
out += look2 + " ";
}
return(out);
}
//_____________________________________________________
int main()
{
std::cout << numstr(tonum("0")) << "\n";
std::cout << numstr(tonum("1")) << "\n";
std::cout << numstr(tonum("2")) << "\n";
std::cout << numstr(tonum("3")) << "\n";
std::cout << numstr(tonum("4")) << "\n";
std::cout << numstr(tonum("5")) << "\n";
std::cout << numstr(tonum("6")) << "\n";
std::cout << numstr(tonum("7")) << "\n";
}
//_____________________________________________________
My code parses an integer into parts and writes them to an array, but now I want to collect the array back into an integer.
I will modify the data inside the array so I need to collect everything back after the changes.
int a = 123456789;
std::string stringInt = std::to_string(a);
std::vector<int> numbers;
numbers.reserve(stringInt.length());
for (const auto& chr : stringInt)
{
// ...
numbers.push_back(chr - '0');
cout << chr << "\n" << endl;
}
You can add up the integers, multiplying the result by 10 every time:
int b = 0;
for (const auto& chr : stringInt)
{
numbers.push_back(chr - '0');
b *= 10;
b += chr - '0';
}
std::cout << b << std::endl;
Alternatively you can put the chars into a string instead of turning them into int and putting them into a vector and then use std::stoi to get an int back out of the string:
std::string numbers;
for (const auto& chr : stringInt)
{
numbers.push_back(chr);
cout << chr << "\n" << endl;
}
int b = std::stoi(numbers);
std::cout << b << std::endl;
I am trying to implement an algorithm that will take a set of numbers and output the largest possible number (without breaking up the individual numbers). So in an example like this where I give 4 numbers:
4
43 12 3 91
The output would be
91-43-3-12 or 9143312.
My attempt is below.
#include <algorithm>
#include <sstream>
#include <iostream>
#include <vector>
#include <string>
using std::vector;
using std::string;
bool compare (int x, int y) {
std::cout << "in func \n";
string a = std::to_string(x);
string b = std::to_string(y);
std::cout << a << " " << b << "\n";
std::cout << std::stoi(a.substr(0, 1)) << " " << std::stoi(b.substr(0, 1)) << "\n" ;
if (std::stoi(a.substr(0, 1)) < std::stoi(b.substr(0, 1))) {
std::cout.flush();
std::cout << "if \n";
return true;
}
else {
std::cout.flush();
std::cout <<"else \n";
return false;
}
}
string largest_number(vector<string> a) {
std::stringstream ret;
while (a.size() > 0) {
int maxNumber =-1;
int index = -1;
std::cout << "going into for " << a.size() << "\n";
for (size_t i = 0; i < a.size(); i++) {
if (! compare (stoi(a[i]), maxNumber ) ) { //stoi(a[i]) >= maxNumber) {
maxNumber = stoi(a[i]);
std::cout << maxNumber << " " << i << "\n";
index = i;
}
std::cout << "here \n";
}
ret << maxNumber;
a.erase(a.begin() + index);
}
string result;
ret >> result;
return result;
}
int main() {
int n;
std::cin >> n;
vector<string> a(n);
for (size_t i = 0; i < a.size(); i++) {
std::cin >> a[i];
}
std::cout << largest_number(a);
}
I do not understand what is wrong with my compare function. When I run it, say with this input:
$ g++ -pipe -O2 -std=c++14 largest_number.cpp -lm -o largest1
$ ./largest1.exe
4
4 23 1 45
going into for 4
in func
4 -1
It doesnt print the cout statements in the conditional if or else. How could this be possible? I even tried flushing. However, if I take the entire conditional out, put a cout statement and the return true or something, then it runs the program in entirety (although this is not the expected output).
I do not mind harsh criticism. What am I doing wrong here? Any advice will be appreciated.
Thanks in advance.
In this statement
std::cout << std::stoi(a.substr(0, 1)) << " " << std::stoi(b.substr(0, 1)) << "\n" ;
when b is equal to -1 the expression b.substr(0, 1) is equal to an object of type std::string that contains one character '-' that is the minus sign.
If to apply the standard function std::stoi to such a string then an exception will be thrown.
Consider the following code snippet
std::string s("-");
try
{
std::stoi(s);
}
catch (const std::exception &e)
{
std::cout << e.what() << std::endl;
}
Its output will be
invalid stoi argument
It seems what you need is just to sort the strings. For example
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
int main()
{
std::vector<std::string> v { "4", "23", "1", "45" };
auto cmp = [](const std::string &a, const std::string &b)
{
std::string::size_type i = 0, m = a.size();
std::string::size_type j = 0, n = b.size();
int result;
do
{
if (m < n)
{
result = a.compare(i, m, b, j, m);
j += m;
n -= m;
}
else
{
result = a.compare(i, n, b, j, n);
i += n;
m -= n;
}
} while (result == 0 && m && n);
return 0 < result;
};
std::sort(v.begin(), v.end(), cmp);
for (const auto &s : v) std::cout << s;
std::cout << std::endl;
return 0;
}
The output of the program will be
454231
Or for this set of numbers
std::vector<std::string> v{ "43", "12", "3", "91" };
the output will be
9143312
or for one more set of numbers
std::vector<std::string> v{ "93", "938" };
the output will be
93938
cout<<"Set B : {";
for(i=0;i<b;i++)
{
cout<<setB[i];
cout<<",";
}
cout<<" }"<<endl;
The code above is not printing correctly. It should print Set B : {1,2,3} but it prints an extra comma ==> Set B : {1,2,3,}
Use
cout << "Set B : {";
for (i = 0; i < b; ++i) {
if (i > 0) cout << ",";
cout << setB[i];
}
cout << " }" << endl;
I changed your algorithm :
Before it meant : "Put the number and then put a comma"
Now it means : "If there is a number behind me put a comma, then put the number"
Before, you always printed a comma when you printed a number so you had an extra comma.
For each iteration of the for loop, the program is going to execute -everything- inside the for loop. So, your loop runs through and prints each number in your set and then a comma.
The problem is that even on your last run through the loop, it is going to print a comma, because it's part of the loop.
cout << "Set B : {";
for(i = 0; i < b; i++){
cout << setB[i];
if (i < (b-1))
cout << ",";
}
cout << " }" << endl;
This code will run the exact same, except the second to last time it runs through the loop, it will not print a comma. No need to get too fancy. :)
Personally I like this solution better. You first print out the first element and then a , [second element].
cout <<"Set B : {" << setB[0];
for(i = 1; i < b; i++)
{
cout << ",";
cout<<setB[i];
}
cout << " }" << endl;
Warning!: This will NOT work if the array is empty.
The loop code prints a pair of number and comma. Try using this one:
cout<<"Set B : {";
for(i=0;i<b;i++)
{
cout<<setB[i];
if(i < b-1) cout<<",";
}
cout<<"}"<<endl;
You're loop is executing the cout << "," 3 times. The following will give what you want:
#include <iostream>
using namespace std;
int main(){
int setB[] = {1,2,3};
cout<<"Set B : {";
for(int i=0;i<3;i++)
{
cout<<setB[i];
if ( i < 2 )
cout<<",";
}
cout<<" }"<<endl;
return 0;
}
The way I often deal with these loops where you want to put something like a space or a comma between a list of items is like this:
int main()
{
// initially the separator is empty
auto sep = "";
for(int i = 0; i < 5; ++i)
{
std::cout << sep << i;
sep = ", "; // make the separator a comma after first item
}
}
Output:
0, 1, 2, 3, 4
If you want to make it more speed efficient you can output the first item using an if() before entering the loop to output the rest of the items like this:
int main()
{
int n;
std::cin >> n;
int i = 0;
if(i < n) // check for no output
std::cout << i;
for(++i; i < n; ++i) // rest of the output (if any)
std::cout << ", " << i; // separate these
}
An other way, without extra branch:
std::cout << "Set B : {";
const char* sep = "";
for (const auto& e : setB) {
std::cout << sep << setB[i];
sep = ", ";
}
std::cout <<" }" << std::endl;
I really like to promote the use of a range library to write declarative code instead of nested for-if statements in an imperative style.
#include <range/v3/all.hpp>
#include <vector>
#include <iostream>
#include <string>
int main()
{
using namespace ranges;
std::vector<int> const vv = { 1,2,3 };
auto joined = vv | view::transform([](int x) {return std::to_string(x);})
| view::join(',');
std::cout << to_<std::string>(joined) << std::endl;
return 0;
}
If you can use STL, try the following:
#include <iterator>
#include <iostream>
int main() {
int setB[]{1,2,3};
std::cout << "Set B : { ";
for(auto i = std::begin(setB), e = std::end(setB); i != e;) {
std::cout << *i;
for(++i; i !=e; ++i) { std::cout << ", " << *i; }
}
std::cout << " }" << std::endl;
return 0;
}
I have a vector array called nVectors.
vector<int>* nVectors[21];
for (int i = 1; i <= 20; i ++) {
nVectors[i] = generateVector(i);
}
I can print all the members of a single vector, but when it comes to the vector array, I still don't know how to print all the vectors in an array.
Maybe an iterator through all the member of a vector array and print using my predefined method pvector can solve this problem? But I don't know how to iterate in gdb.
std::array<std::vector<int>*, 21> nVectors;
for(std::array<std::vector<int>*>::iterator i = nVectors.begin();
i != nVectors.end();
++i)
{
for(std::vector<int>::iterator it = (*i)->begin();
it != (*i)->end();
++it)
{
std::cout << *it << " ";
}
}
std::cout << std::endl;
Or, in C++11:
std::vector<int>* nVectors[21];
for(auto &i : nVectors)
{
for(auto &it : i)
{
std::cout << *it << " ";
}
}
std::cout << std::endl;