I'm trying to write a little program to create a vector of random integer sets, but the problem is once the first set is created the program keeps storing the same set of numbers in subsequent iterations. Any help to explain or correct this problem would be very much appreciated. Thanks!
#include<iostream>
#include<cstdlib>
#include<ctime>
#include<set>
#include<vector>
using namespace std;
typedef set<int> Set_I;
typedef set<int>::iterator It;
typedef vector<set<int> > vec_Set;
int random();
void print_set(Set_I s);
void print_vec(vec_Set v);
int main()
{
srand(time(0));
Set_I s;
vec_Set v;
v.resize(4);
for(int i=0; i<4;i++)
{
//cout << s.size() << " " <<endl;
while(s.size()<6)
{
s.insert(random());
}
v[i] = s;
s.empty();
}
//print_set(s);
print_vec(v);
cout << endl << s.size() <<endl << v.size();
system("PAUSE");
}
int random()
{
int r = 1 + rand()%49;
return r;
}
void print_set(Set_I s)
{
for(It it=s.begin(); it!=s.end(); it++)
{
cout << *it << " ";
}
cout << endl;
}
void print_vec(vec_Set v)
{
for(int i=0;i<v.size();i++)
{
cout << "{ ";
for(It j = v[i].begin() ; j != v[i].end() ;j++)
{
cout << *j << " ";
}
cout <<"}";
cout <<endl;
}
}
s.empty() returns a bool stating that the set is empty or not. It has no effect on the members of the set!!
you have to use s.clear() for emptying (clearing) your set.
Related
I was working with vector and trying to work with erase function from vector library.
Here is my code
#include <iostream>
#include <vector>
int leftover(std::vector<int> aList)
{
// size = 1 will be termination point
if (aList.size() == 1)
{
return aList.at(0);
}
else
{
aList.push_back(aList.at(0));
aList.erase(aList.at(0));
aList.erase(aList.at(1));
return leftover(aList);
}
}
int main()
{
int x;
std::cout << "Enter a number: ";
std::cin >> x;
std::vector<int> intVector;
for (int i = 0 ; i < x; i++) {
intVector.push_back(i+1);
}
for (const int& i : intVector)
{
std::cout << i << " ";
}
std::cout << "\n";
//int leftwith = leftover(intVector);
//std::cout << leftwith << "\n";
return 0;
}
Anything with remove the element at particular position would be much appreciated.
I usually return an object of std::vector or std::map as an incoming reference paremeter(as funcVec2 and funcMap2 below). But it is a bit inconvenient when writing codes. So I think if I can use return value under c++11(as funcVec1 and funcMap1 below) because it will call move constructor but not copy constructor, so it maybe still spend only one construct time and no deconstruct as the form of incoming reference paremeter.
But I write the codes below to verify it and it turns out that funcVec1 and funcMap1 takes more times then funcVec2 and funcMap2. So I am confused now why funcVec1 and funcMap1 takes so long?
#include <iostream>
#include <vector>
#include <map>
#include <chrono>
using namespace std;
vector<int> funcVec1() {
vector<int >vec;
for (int i = 0; i < 10; ++i) {
vec.push_back(i);
}
return vec;
}
void funcVec2(vector<int>&vec) {
for (int i = 0; i < 10; ++i) {
vec.push_back(i);
}
return;
}
map<int, int> funcMap1() {
map<int, int>tmpMap;
for (int i = 0; i < 10; ++i) {
tmpMap[i] = i;
}
return tmpMap;
}
void funcMap2(map<int, int>&tmpMap) {
for (int i = 0; i < 10; ++i) {
tmpMap[i] = i;
}
}
int main()
{
using namespace std::chrono;
system_clock::time_point t1 = system_clock::now();
for (int i = 0; i < 100000; ++i) {
vector<int> vec1 = funcVec1();
}
auto t2 = std::chrono::system_clock::now();
cout << "return vec takes " << (t2 - t1).count() << " tick count" << endl;
cout << duration_cast<milliseconds>(t2 - t1).count() << " milliseconds" << endl;
cout << " --------------------------------" << endl;
vector<int> vec2;
for (int i = 0; i < 100000; ++i) {
funcVec2(vec2);
}
auto t3 = system_clock::now();
cout << "reference vec takes " << (t3 - t2).count() << " tick count" << endl;
cout << duration_cast<milliseconds>(t3 - t2).count() << " milliseconds" << endl;
cout << " --------------------------------" << endl;
for (int i = 0; i < 100000; ++i) {
map<int, int> tmpMap1 = funcMap1();
}
auto t4 = system_clock::now();
cout << "return map takes " << (t4 - t3).count() << " tick count" << endl;
cout << duration_cast<milliseconds>(t4 - t3).count() << " milliseconds" << endl;
cout << " --------------------------------" << endl;
map<int, int>tmpMap2;
for (int i = 0; i < 100000; ++i) {
funcMap2(tmpMap2);
}
auto t5 = system_clock::now();
cout << "reference map takes " << (t5 - t4).count() << " tick count" << endl;
cout << duration_cast<milliseconds>(t5 - t4).count() << " milliseconds" << endl;
cout << " --------------------------------" << endl;
return 0;
}
you are not only meassuring the time for your operations, you also include the printouts. this is suboptimal.
you should measure performance in release mode. be aware that you are not doing anything usefull with your objects and the optimizer may throw away most of your code you wanted to measure.
the comparisons are not "fair". for example in your map1 case you are constructing an empty map, fill it (memory allocations happen here) and then you throw it away. in the map2 case you are reusing the identical map object over and over again. you are not allocating memory over and over again.
This is my assignment, i finished writing my code and it does compile but it is not giving the right answer. So i know there is some logical error but i cannot find out what.
Plz check and tell me, simple code to calculate permutations and combinations
#include <iostream>
using namespace std;
int factorial(int n)
{
if (n == 0 or n == 1)
{
return 1;
}
else
{
return n * factorial(n - 1);
}
}
int permutation(int a, int b)
{
//factorial(a);
int perm = factorial(a) / factorial(a - b);
return perm;
}
int combination(int a, int b)
{
int permutation(int a, int b);
int factorial(int n);
return permutation(a, b) / factorial(b);;
}
int main()
{
int n;
int r;
cout << "Enter n: " << endl;
cin >> n;
cout << "Enter r: " << endl;
cin >> r;
int factorial(int n);
int permutation(int n, int r);
int combination(int n, int r);
if (n >= r)
{
cout << "Permutuation: " << permutation << endl;
cout << "Combination: " << combination << endl;
}
else
{
cout << "Invalid" << endl;
}
return 0;
}
The answer given by the console
Enter n:
6
Enter r:
5
Permutuation: 00AC1375
Combination: 00AC133E
There are a number of errors in your code. First, you should not re-declare your 'permutation' and 'combination' functions inside other functions.
EDIT: Actually, this is not an error but, in my opinion, very bad practice. You could accidentally 'hide' the actual function declaration, which is already provided as you have defined both before any of the calling functions.
Second, your cout << permutation << endl; code is printing a function! This will be taken as meaning the address of that function, which is what you are seeing (HEX addresses).
Here's a 'fixed' version that works (with comments).
#include <iostream>
#include <iso646.h> // Need this in order to use "or" in place of "||"
using namespace std;
int factorial(int n)
{
if (n == 0 or n == 1) {
return 1;
}
else {
return n * factorial(n - 1);
}
}
int permutation(int a, int b)
{
//factorial(a);
int perm = factorial(a) / factorial(a - b);
return perm;
}
int combination(int a, int b)
{
// int permutation(int a, int b); // You don't need to redeclare function inside another one ...
// int factorial(int n);
return permutation(a, b) / factorial(b);;
}
int main()
{
int n, r;
cout << "Enter n: " << endl;
cin >> n;
cout << "Enter r: " << endl;
cin >> r;
// int factorial(int n);
int p = permutation(n, r); // This is how to call your functions ...
int c = combination(n, r); // and assign their returns to values.
if (n >= r) {
cout << "Permutuation: " << p << endl; // Output the values ...
cout << "Combination: " << c << endl; // ...from the functions
}
else {
cout << "Invalid" << endl;
}
return 0;
}
Feel free to ask for further explanations if there's anything I've done that you don't understand.
I'm attempting to print out the contents of a 2d vector in the same fashion in which they are initialized.
#include <iostream>
#include <vector>
using namespace std;
int main(){
vector<vector<int > > frontier = {{-1,0}, {1,0}, {0,-1}, {0,1}};
for (int i = 0; i < frontier.size(); i++) {
for (int j = 0; j < frontier[i].size(); j++) {
std::cout << frontier[i][j] << ", ";
}
}
cout << "End of frontier. " << endl;
/* This below is an implementation that I found online but found
no
* way to be able to implement the column reference.
*/
for (int i = 0; i < frontier.size(); ++i) {
for (int j = 0; j < col; ++j) {
cout << frontier[i + j * col] << ' ';
}
cout << endl;
}
}
This is to determine the contents of a 2d vector. So far, this code can print out every index separated by a comma. I, on the other hand, need to write code that will signify where a new vector begins.
output:
-1, 0, 1, 0, 0, -1, 0, 1,
expected output:
{{-1,0}, {1,0}, {0,-1}, {0,1}}
Here's how I might do it:
#include <iostream>
#include <vector>
#include <string>
int main()
{
std::vector<std::vector<int>> frontier = { {-1,0}, {1,0}, {0,-1}, {0,1} };
std::string outerPrefix = "";
std::cout << "{";
for(const auto& outer : frontier)
{
std::cout << outerPrefix << "{";
std::string innerPrefix = "";
for(auto inner : outer)
{
std::cout << innerPrefix << inner;
innerPrefix = ",";
}
std::cout << "}";
outerPrefix = ", ";
}
std::cout << "}";
}
Output: {{-1,0}, {1,0}, {0,-1}, {0,1}}
In the first example I used a range-based for loop. If you're familiar with the concept of foreach in many languages it's basically the same thing. If you don't need an actual index variable it is safer because you don't have to worry about being off by one and indexing outside the container. It also works the same way on containers like map or set where you would need to use iterators rather than an index.
If you were to do the same thing with nested index loops like you had in your original it might look something like this:
#include <iostream>
#include <vector>
#include <string>
int main()
{
std::vector<std::vector<int>> frontier = { {-1,0}, {1,0}, {0,-1}, {0,1} };
std::cout << "{";
for(size_t outer = 0; outer < frontier.size(); ++outer)
{
if (outer != 0)
{
std::cout << ", ";
}
std::cout << "{";
for(size_t inner = 0; inner < frontier[outer].size(); ++inner)
{
if (inner != 0)
{
std::cout << ",";
}
std::cout << inner;
}
std::cout << "}";
}
std::cout << "}";
}
My program can't read all of the data from my MarvelIn.txt file.
It reads about 29 spaces in, and MarvelIn.txt contains only 9 entries, then I get a runtime error.
I think I have all the syntax right, however this is the only error I have. It will not output to the output file "MarvelOut.txt".
Here is the code:
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <stdio.h>
using namespace std;
struct sstruct
{
string first, last;
string department;
int salary;
};
void init2(sstruct s[50])
{
int maxarray = 50;
sstruct init = { "Darth", "Vader", "None", 0 };
for (int i = 0; i < maxarray; i++) {
s[i] = init;
cout << "init: " <<s[i].first<<endl;
}
}
void read(sstruct s[50], int &nums)
{
int maxarray = 50;
ifstream inf("MarvelIn.txt");
int i = 0;
while (!inf.eof())
{
inf >> s[i].first >> s[i].last >> s[i].department >> s[i].salary;
cout << "read: "<<s[i].first<<s[i].last << s[i].department <<
s[i].salary << endl;
i++;
}
nums = i;
}
void avg(sstruct s[50], int &nums, double &average2)
{
int maxarray = 50;
int i;
for (i = 0; i < nums; i++)
average2 += s[i].salary;
average2 /= nums;
}
void print(sstruct s[50], int nums, double &average2)
{
int maxarray = 50;
ofstream outf("MarvelOut.txt");
int i = 0;
string temp;
outf << "the number of professors is: " << nums << endl;
cout << "the number of professors is: " << nums << endl;
outf << endl << "The average salary of the professors is: " << average2 << endl;
outf << "Advisor " << "Major " << " Department " << "Salary " << endl;
for (i = 0; i < nums; i++)
{
temp= s[i].last + "," + s[i].first;
cout << "last, first " << temp << endl;
outf << left << setw(20) << temp << right << setw(5)<< s[i].department << setw(5) << s[i].salary << setw(8) << endl;
}
outf << endl << endl;
}
void swap(sstruct &a, sstruct &b)
{
sstruct temp;
temp=a;
a=b;
b=temp;
}
void bubbleSort(sstruct s[50], int &nums)
{
int maxarray = 50;
int i, j;
bool swapped;
for (i = 0; i < nums - 1; i++)
{
swapped = false;
for (j = 0; j < nums - i - 1; j++)
{
if (s[j].department > s[j + 1].department)
{
swap(s[j], s[j+1]);
swapped = true;
}
}
// IF no two elements were swapped by inner loop, then break
if (swapped == false)
break;
}
}
int main() {
int nums=0;
double average3=0.0;
const int maxarray = 50;
sstruct s[maxarray];
init2(s);
print(s, nums, average3);
read(s, nums);
cout << "numsfirst: " << nums << endl;
avg(s, nums, average3);
cout << "nums" << nums << endl;
bubbleSort(s,nums);
print(s, nums, average3);
system("pause");
return 0;
}