I have made this code that should build two vectors, one with the integers up to 100 and the other with the squares of these integers, and would like to write two columns so that the values line up in two columns. The program compiles ok, but the output is empty, i.e., nothinkg appears but only the message "Process returned 0 (0x0)". What exactly am I missing here?
#include <iostream>
#include <cmath>
#include <iomanip>
#include <vector>
using namespace std;
int main()
{
vector<int> numbers;
typedef vector<int>::size_type vec_sz;
vec_sz size = numbers.size();
for (vec_sz i = 0; i != numbers.size(); ++i)
{
numbers.push_back(i);
}
vector<int> squares;
for (vec_sz i = 0; i!= squares.size(); i++)
{
squares.push_back(i^2);
}
for (vec_sz i = 0; i != numbers.size(); ++i)
{
cout << setw(3)
<< numbers[i]
<< setw(6)
<< squares[i]
<< endl;
}
return 0;
}
When you write this line at the beginning of your main function,
vec_sz size = numbers.size();
you want to obtain the size of the vector. However, numbers is empty, it does not contain any data. Hence size will be 0. Here numbers.size() is going to return 0.
Hence for (vec_sz i = 0; i != numbers.size(); ++i) will not execute even once.
Let's say that you want to fill numbers, then you should know how many values do you want to fill in numbers. Once you know this value, store it in a variable let's say count.
Sample:
const int count = 10;
for (int i = 0; i < count; ++i) {
numbers.push_back(i);
}
// now numbers.size() will return 10;
Same goes for your squares vector.
Related
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
int main()
{
vector<double> numbers(input_number);
cout << "Enter numbers from 0 to 50: " << endl;
for (int i = 0; i < input_number; ++i) {
cin >> numbers[i];
}
unordered_map<int, int> freq;
for (int i = 0; i < numbers.size(); i++) {
freq[numbers[i]]++;
}
for (int i = 0; i < numbers.size(); i++) {
cout << freq[numbers[i]];
}
return 0;
}
When the use inputs numbers, for example 1,1,1,2 the output should be "1" because it is the most frequent number but the output here became "3,3,3,1" How to solve this problem?
You are most of the way there. Your frequencies are all stored, and you just need to search through the unordered_map now to find the item that has the largest value. Since you're already using <algorithm> you can leverage std::max_element to help:
#include <algorithm>
#include <iostream>
#include <unordered_map>
#include <vector>
int main()
{
std::vector<int> numbers = { 1, 2, 3, 2, 3, 2, 2 };
std::unordered_map<int, int> freq;
for (int n : numbers) ++freq[n];
if (!freq.empty())
{
auto it = std::max_element(freq.begin(), freq.end(),
[](const auto& a, const auto& b) { return a.second < b.second; });
std::cout << "Most frequent is " << it->first << "\n";
}
}
Output:
Most frequent is 2
Here, a custom comparison function is supplied that tests only the frequency part of the element (otherwise the default behavior will compare the full key/value pairs which will result in finding the largest number).
Note that because the map is unordered, there won't be a predictable outcome for tie-breakers (where more than one number is the most frequent). If you need to handle that in a more predictable way, you'll need to adjust the comparison function or possibly just loop over the container yourself if it requires additional work.
One option for tie-breaking is to choose the lowest number. That could be achieved by modifying the comparison to:
return std::make_pair(a.second, b.first) < std::make_pair(b.second, a.first);
The problem is that you just output all the values in map. In a naive implementation you have to iterate through map and register the maximum value and it's frequency:
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
int main()
{
using std::cin, std::cout, std::endl;
using std::vector, std::unordered_map;
int input_number = 0, max_freq = 0, max_val = 0;
cout << "How many numbers you want to input: " << endl;
cin >> input_number;
// Making input double may creates questions
vector<int> numbers(input_number);
cout << "Enter numbers from 0 to 50: " << endl;
for (int i = 0; i < input_number; ++i) {
cin >> numbers[i];
}
unordered_map<int, int> freq;
for (int i = 0; i < numbers.size(); i++) {
freq[numbers[i]]++;
}
// iterating over the map and finding max value
for (auto val : freq) {
if( val.second > max_freq) {
max_val = val.first;
max_freq = val.second;
}
}
cout << max_val;
return 0;
}
Standard maps do store values as pairs of key and value (std::pair). This can be done in easier way: you can do that right while inputting the numbers.
for (int i = 0; i < numbers.size(); i++) {
int val = numbers[i];
int curfreq = ++freq[val];
if (curfreq > max_freq) {
max_val = val;
max_freq = curfreq;
}
}
cout << max_val;
Your array freq has to proper values in it. But your logic in the print out is wrong. You are printing the numbers twice. I guess you want to print all the numbers from 0 to 50.
cout << freq[i]
Then you see which entries have values or not. Then add some logic (which doesn't exist in your code) to pick the proper value. Like the biggest count..
I have tried to do some practice with vector, and I made a simple for loop to calculate the sum of the elements within the vector. The program did not behave in the way I expect, so I try to run a debugger, and to my surprise, somehow, the compiler skips the for loop altogether, and I have not come up with a reasonable explanation.
//all code is written in cpp
#include <vector>
#include <iostream>
using namespace std;
int simplefunction(vector<int>vect)
{
int size = vect.size();
int sum = 0;
for (int count = 0; count == 4; count++) //<<--this for loop is being skipped when I count==4
{
sum = sum + vect[count];
}
return sum; //<<---the return sum is 0
}
int main()
{
vector<int>myvector(10);
for (int i = 0; i == 10; i++)
{
myvector.push_back(i);
}
int sum = simplefunction(myvector);
cout << "the result of the sum is " << sum;
return 0;
}
I have done some research, and usually the ill-defined for loop shows up when the final condition cannot be met (Ex: when setting count-- instead of count++)
Your loop's conditions are wrong, as they are always false!
Look at to the loops there
for (int i = 0; i == 10; i++)
// ^^^^^^^-----> condition : is it `true` when i is 0 (NO!!)
and
for (int count=0; count==4; count++)
// ^^^^^^^^^-----> condition : is it `true` when i is 0 (NO!!)
you are checking i is equal to 10 and 4 respectively, before incrementing it. That is always false. Hence it has not executed further. They should be
for (int i = 0; i < 10; i++) and for (int count=0; count<4; count++)
Secondly, vector<int> myvector(10); allocates a vector of integers and initialized with 0 s. Meaning, the loop afterwards this line (i.e. in the main())
for (int i = 0; i == 10; i++) {
myvector.push_back(i);
}
will insert 10 more elements (i.e. i s) to it, and you will end up with myvector with 20 elements. You probably meant to do
std::vector<int> myvector;
myvector.reserve(10) // reserve memory to avoid unwanted reallocations
for (int i = 0; i < 10; i++)
{
myvector.push_back(i);
}
or simpler using std::iota from <numeric> header.
#include <numeric> // std::iota
std::vector<int> myvector(10);
std::iota(myvector.begin(), myvector.end(), 0);
As a side note, avoid practising with using namespace std;
I'm having trouble creating a Matrix using Vectors. The rows and columns will all be random doubles and I am trying to fill it in.
I have tried to initialize the size of the vector before hand, I believe it initializes correctly, however, when I try to push onto the rows and columns I get very odd output. Here is my Header File:
#ifndef MATRIX_NORM_HPP
#define MATRIX_NORM_HPP
#include <vector>
class MatrixNorm
{
public:
void initProgram();
void printResults();
double randNumber();
private:
std::vector<std::vector<double>> M;
double mNorm1 = 0.0;
double mNormInf = 0.0;
};
#endif
Here is my CPP File:
#include "matrixNorm.hpp"
#include <iostream>
#include <random>
void initProgram()
{
double ranNum = 0.0;
int size = 0;
std::cout << "Please enter a size of an n by n Matrix: ";
std::cin >> size;
std::vector<std::vector<double>> temp(size, std::vector<double>(size));
for(int i = 0; i < size; ++i)
{
for(int j = 0; j < size; ++j)
{
ranNum = randNumber();
temp[i].push_back(ranNum);
temp[j].push_back(ranNum);
}
}
M = temp;
printResults();
}
void MatrixNorm::printResults()
{
for(auto &&e: M)
{
for(auto && f: e)
{
std::cout << f << " ";
}
std::cout << std::endl;
}
}
double MatrixNorm::randNumber()
{
double ranDouble = 0.0;
std::random_device rd;
std::default_random_engine generator(rd());
std::uniform_real_distribution<double> unif(-1000.0,1000.0);
ranDouble = unif(generator);
return ranDouble;
}
The output I receive when I run the program from main.cpp is:
Please enter a size of an n by n Matrix: 3
0 0 0 792.208 792.208 -361.248 -776.871 742.521 116.732
0 0 0 -361.248 742.521 411.965 411.965 909.313 -50.0048
0 0 0 -776.871 909.313 116.732 -50.0048 79.6189 79.6189
As you can see, it seems to get the column size correctly, but it does not get the row size correctly, and if you look very closely. Some of the numbers are duplicates, I wish I knew how to format it more clearly but if you start at the top left you see 792.208 792.208 then go down a row and you see 411.965 411.965 and last it finishes off at 79.6189 79.6189 in the lower right.
What am I doing wrong? How do I do this correctly? Any help would be appreciated.
Seems to me that the correct way to initialize your matrix is:
(...)
std::vector<std::vector<double>> temp;
for(int i = 0; i < size; ++i)
{
std::vector<double> k;
for(int j = 0; j < size; ++j)
{
ranNum = randNumber();
k.emplace_back(ranNum);
}
temp.emplace_back(k);
}
(...)
Explanation:
with this constructor:
std::vector<std::vector<double>> temp(size, std::vector<double>(size));
you are creating size copies of default vector constructed of size elements (std::vector<double>(size)). In other words, you have a size x size matrix.
So, instead of pushing new values in your code, you should be changing it. In the code I proposed, it is just simpler to populated this matrix when you are creating it.
Hello I am trying to split an array any time there is a negative value (excluding the negative value) and am a bit stuck at the moment. I tried an approach as seen in my code but I am not getting the desired output.
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;
int main()
{
string line;
string filename;
int n,length;
std::vector<int>arr1;
fstream file("t1.txt");
if(file.is_open())
{
while(file >> n)
arr1.push_back(n);
for(int i =0; i < (int)arr1.size(); i++)
cout << arr1.at(i);
}
cout << endl;
int* arr2 = &arr1[0];
int arr3[arr1.size()/2];
int arr4[arr1.size()/2];
for(int i = 0; i < arr1.size(); i++)
{
cout << arr2[i];
}
for (int i =0; i < arr1.size(); i++)
{
if(i == -1)
break;
else
arr3[i] = arr2[i];
}
return 0;
}
The main problem is here:
int arr3[arr1.size()/2];
int arr4[arr1.size()/2];
This doesn't compile, and can be replaced with
std::vector<int> arr3; arr3.reserve(arr1.size() / 2);
std::vector<int> arr4; arr4.reserve(arr1.size() / 2);
I've added the "reserve" function so that the program doesn't have to allocate memory over and over in the loop.
Next, you are checking i in your loop, and your i loops from 0 to arr1.size() (which is unsigned so can't be negative) therefore i will never be negative.
What you really wanna check is what is in the arr1 vector at "i" position, and you can do so with the [] operator like
for (int i =0; i < arr1.size(); i++)
{
if (arr1[i] >= 0) //if the value is positive, we push it inside our arr3 vector
arr3.push_back(arr1[i]);
else
{
i++; //skip negative value
//
while (i < arr1.size())
{
if (arr1[i] > 0)
arr4.push_back(arr1[i]);
i++;
}
//
//or
//insert all the elemenents we haven't processed yet in the arr4 vector
//this code assumes those elements are positive values
//arr4.insert(arr4.begin(), arr1.begin() + i, arr1.end());
//break;
}
}
Of course this could be done in a different way, like instead of creating 2 vectors, you could just use the one you have generated already.
Hope this helps.
There are several problems in your code
you should not access the vector's data this way unless you really need to
you prepare arrays with predefined size without knowing where to expect the negative values
you do not assign anything to your array 4
you check the index for being negative, not the value
according to your text there could be several negative values leading to multiple result-arrays. You seem to be prepared for only two.
Here is some code that actually splits when encountering negative values:
std::vector<vector<int> > splitted;
for (int i = 0; i < arr1.size(); ++i)
{
if (i ==0 or arr1[i] < 0)
splitted.push_back(std::vector<int>());
if (arr1[i] >= 0)
splitted.back().push_back(arr1[i]);
}
Testing it:
for (int i = 0; i < splitted.size(); ++i)
{
for (int k = 0; k < splitted[i].size(); ++k)
{
std::cout << splitted[i][k];
}
if (splitted[i].empty())
std::cout << "(emtpy)";
std::cout << '\n';
}
Using the following test input
1 2 3 -1 1 -1 -1
You get the following output:
123
1
(emtpy)
(emtpy)
My homework program has to write random numbers for arrival time and burst time into a file. Then after they are written, it reads the file and sorts the contents.
I figured setting up a 2d array would be the easiest way for me to go about this. But I am unsure on how to implement my sort so that if an arrival time swaps places then burst time of that arrival goes along for the ride.
I feel like I worded that poorly, but a basic example would be:
array[3][10] > array[2][23]
So since second array has an earlier arrival time I need both its arrival 2 and its burst 23 to move before array[3][10], but I need this do that and compare 100 inputs.
#include <iostream>
#include <cstdlib>
#include <iomanip>
#include <fstream>
const int max = 100;
using namespace std;
int main()
{
multimap<int [][]> myMap;
int randomBurst[max];
int arrivalTime[max];
int line[max][2];
int first = 0;
for (int i = 0; i < 100; i++)
{
if (i < 100)
{
ofstream write("Schedule.txt", ios::app);
randomBurst[i] = rand() % 1000;
arrivalTime[i] = rand() % 1000;
write << arrivalTime[i] << " " << randomBurst[i] << endl;
}
}
ifstream read("Schedule.txt");
for (int i = 0; i <= max; i++)
{
for (int j = 0; j < 2; j++)
{
read >> line[i][j];
cout << line[i][j] << " " ;
}
cout << endl;
}
cout << endl;
cout << endl;
for (int i = 0; i <= max; i++)
{
for (int j = 0; j < 2; j++)
{
myMap.insert(pair<int[][]>(line[i][j]);
}
cout << endl;
}
system("pause");
return 0;
}
My code sets up my array correctly after it reads the written file content, but I'm kind of lost what I should implement for a sort.
Well coming forward with this, mainly left that comment to be able to find this question faster on my laptop.
Like I said in the comment, if you want a presorted, by key value 2D "array", the quickest manner in which you could do this is with the map container., and if you really need the internal points to be ordered, and you will be using multiple entries within it, lets say entries 2,30 2,12 ... You could either build a map of vectors, or arrays, or use a Multimap. Not too sure of this data structure, as I have never really had a reason to use it as of yet. Referenced here http://www.cplusplus.com/reference/map/multimap/
The above will provide you with the sorting done for you, and the reason why I recommended a vector is the lack of order within it, and not sure if the 'bursts?' are to be ordered as well.
EDIT:
Forgot to mention, that a map will not hold more than one key of any given value, so if you are, again, inputting multiple points a above, then you will. if implementing things as you were before, overwrite things.
EDIT:
So this is more or less the fix I think I have, but you are working around this in a very indirect manner, that is hard to follow honestly.
#include <map>
#include <iostream>
#include <cstdlib>
#include <iomanip>
#include <fstream>
using namespace std;
const int MAX = 100;
int main()
{
multimap<int,int> myMap;
int randomBurst[100];
int arrivalTime[100];
int line[100][2];
int first = 0;
for (int i = 0; i < 100; i++)
{
if (i < 100)
{
ofstream write("Schedule.txt", ios::app);
randomBurst[i] = rand() % 1000;
arrivalTime[i] = rand() % 1000;
write << arrivalTime[i] << " " << randomBurst[i] << endl;
}
}
ifstream read("Schedule.txt");
for (int i = 0; i <= 100; i++)
{
for (int j = 0; j < 2; j++)
{
read >> line[i][j];
cout << line[i][j] << " " ;
}
cout << endl;
}
// cout << endl;
// cout << endl;
for (int i = 0; i < 100; i++)
{
for (int j = 0; j < 2; j++)
{
//Attain the value in the index, and the held value within it.
myMap.insert(pair<int, int> (line[i][j], line[i][j]));
}
cout << endl;
}
// system("pause");
return 0;
This fixes the insertion point, just because you give it an array it does not mean that the program will take that as a pair, as the first index is a point to another array in itself. And so on. I recommend starting off wiht a map object instead, as the multimap makes things a bit annoying, if you are familiar with the vector containers then use that instead within the map to log multiple values.