I still have the same problem of wierd number in my arrays, but this time in a different function:
#include <iostream>
using namespace std;
//First Array
int n[20];
int i, a;
//Second Array
int n2[20];
int i2, a2;
void arraySelection();
void printArrays();
void unionArray();
void intersectionArray();
int main(){
arraySelection();
printArrays();
intersectionArray();
unionArray();
return 0;
}
void arraySelection(){
cout << "First array size: ";
cin >> a;
cout << "Array elements: " << endl;;
for (i = 0; i < a; i++){
cin >> n[i];
}
cout << "\nSecond array size: ";
cin >> a2;
cout << "Array elements: " << endl;;
for (i2 = 0; i2 < a2; i2++){
cin >> n2[i2];
}
}
void unionArray(){
const int riemp = 40;
int unionNums[riemp];
int j, x, y, z;
bool t = false;
for (j = 0; j <= riemp; j++){
unionNums[j] = n[j];
cout << unionNums[j] << " ";
}
}
Basically I am trying to copy the numbers of my first array n[20] into my unionNums[40] array. It actually does that but it also outputs a series of 0s and other large wierd numbers. 2 Days in the go and still no idea. (PS If i try to gife fixed numbers to the array, so getting rid of the user input, it goes without any problem whatsoever) I also did not bother copyng my intersectionArray and printArray functions since they do things that I don't need anymore at this point
Here you read in elements up to n[a-1]:
for (i = 0; i < a; i++){
cin >> n[i];
}
So all elements up to n[a-1] are initialized. Then you print all elements up to n[a], however.
for (i = 0; i < a+1; i++){ // note that you have "a+1" here, not just "a"
cout << n[i] << " - ";
}
n[a] wasn't initialized. When you read that out, it's undefined behavior. That often manifests as getting a garbage value, which is what you're seeing in your output. The same thing happens in your second array/loop where you write into the array for i2 < a2 but get output for i2 < a2+1.
Related
The strange problem appears in my program. It is working, but in debugging it shows the "Exception thrown" in random places at the outputting
cout<<"Average value:"<<u3.apr();
_getch();
Sometimes, it even throws this error after the main function (Behind the {})
It is quite annoying because the program just closes after 3 seconds because of these errors.
(Maybe that's because of class, but I'm trying to learn it ;) )
Have tried already changing lines order, rewriting class name and array name.
#include <iostream>
#include <conio.h>
using namespace std;
class vid
{
private:
int i, j;
double rez, sum=0;
public:
int size;
double *arr = new double[size];
double apr()
{
for (i = 0; i < size; i++)
{
sum += (*(arr + i));
}
return sum / size;
}
};
int main()
{
vid u3;
cout << "Enter array length:";
cin >> u3.size;
for (int i = 0; i < u3.size; i++)
{
cout << "Enter array's " << i << " element:" << endl;
cin >> *(u3.arr+i);
}
cout << "Your array:" << endl;
for (int i = 0; i < u3.size; i++)
{
cout << *(u3.arr + i) << "\t";
}
cout << endl;
cout<<"Average value:"<<u3.apr();
_getch();
}
Thanks for any help ;)
arr is initialised when u3 is constructed.
But you didn't populate u3.size until later.
So, your array has indeterminate length (which is already UB), and your accesses later may be invalid.
You're going to have to manage your class's member a bit more cleverly!
Such classes generally have a "resize" function that performs the allocation per the requested size. Don't forget to safely kill any prior allocation, transplanting data if necessary. You can find online plenty of examples of a vector implementation.
Certainly renaming classes and randomly re-ordering the lines of your program's source code is not going to solve anything.
u3.size is not set until after u3 is constructed. By setting u3.size you can avoid this compiler-time error.
It seems that as an alternative solution, you might want to consider how to get rid of the new call and the need to write a destructor that will delete arr.
By creating a constructor that takes a size parameter AND by switching arr to a std::vector, you can allow the class to hold the vector and handle memory allocation and deallocation:
#include <iostream>
#include <vector>
using namespace std;
class vid
{
private:
int i, j;
double rez, sum=0;
public:
int size;
std::vector<double> arr;
// constructor requires size to be passed in;
// constructor initializes the arr array with the passed in size to zeroes.
vid(int argSize) : size(argSize), arr(argSize, 0.0){ }
double apr()
{
for (i = 0; i < size; i++)
{
sum += arr[i];
}
return sum / size;
}
};
int main()
{
uint size;
cout << "Enter array length:";
cin >> size;
vid u3(size);
for (int i = 0; i < u3.size; i++)
{
cout << "Enter array's #" << i << " element:" << endl;
cin >> u3.arr[i];
}
cout << "Your array:" << endl;
for (int i = 0; i < u3.size; i++)
{
cout << u3.arr[i] << "\t";
}
cout << endl;
cout<<"Average value:"<<u3.apr();
char ch;
cin >> ch;
}
I need to write a program that receives 2 arrays and checks how many times 1 is included in the other...
But I cant find what is wrong with my program! tx!!
#include <iostream>
using namespace std;
int main()
{
int vector1[500];
int vector2[100];
int a = 0, b = 0, count = 0, k = 0;
cout << "enter size of first array:" << endl;
cin >> a;
cout << " enter first array values:" << endl;
for (int i = 0; i < a; i++)
cin >> vector1[i];
cout << "enter size of second array:" << endl;
cin >> b;
cout << "enter secound array values:" << endl;
for (int i = 0; i < b; i++)
cin >> vector2[i];
for (int i = 0; i < b; i++)
for (int j = 0; j < a; j++)
if (vector2[i + k] == vector1[j])
{
count++;
k++;
}
else
k = 0;
cout << count << endl;
system("pause");
return 0;
}
Why at all do you need k? The problem is about all inclusions of all elements right? If O(n^2) complexity is fine, then...
for (int i = 0; i < b; i++)
for (int j = 0; j < a; j++)
if (vector2[i] == vector1[j])
count++;
One obvious disadvantage of the code above is that you'll get the total sum of all occurences of elements from vector1 in vector2. The key idea remains the same in case you need to know, which elements exactly appeared in another array and how many times, you'll just have to use map or other vector.
*Edit: Still, when input 3 columns for the 1st row and 2 columns for the 2th, in the output 1st row becomes 2-elemented as the first.
Problem with outputting dynamically allocated number of equipes with separately dynamically allocated number of columns (for number of catches for the each equip)... Namely, if I try to allocate 2 equipes and then for the first equip two "catches" of fish (two columns) and for second equip three catches of fish, everything is o.k.... but if I try input of smaller number of columns ("catches") for the second row (equip) then in the output the "excess" of the first row is "cutted off", so for example if there where a 3 columns input for the 1st row and 2 columns input for the second row, in the output there will be just two columns (indices of numbers) for the every of the two rows.
#include<iostream>
int main()
{
using namespace std;
int *sum;
int *a = new int;
int *b = new int;
cout << "Total number of equips: ";
cin >> *a;
// Allocate a two-dimensional 3x2 array of ints
int** ippArray = new int*[*a];
for (int i = 0; i < *a+1; ++i) {
ippArray[i] = new int[*b];
}
// fill the array
for (int i = 1; i < *a+1; ++i) {
cout << "Total number of catches for " << i << "th equip : ";
cin >> *b;
cout << "Equip number: " << i << endl;
for (int j = 1; j < *b+1; ++j) {
cout << "Catch number: " << j << endl;
cin >> ippArray[i][j];
ippArray[i][j];
}
}
// Output the array
for (int i = 1; i < *a+1; ++i) {
for (int j = 1; j < *b+1; ++j) {
cout << ippArray[i][j] << " ";
*sum = *sum + ippArray[i][j];
}
cout << endl;
}
cout << endl;
cout << "All catches of the all equipes: " << *sum-3;
// Deallocate
for (int i = 1; i < *a+1; ++i) {
delete [] ippArray[i];
}
delete [] ippArray;
// Keep the window open
cin.get();
return 0;
}
First, don't make your integers into pointers (int *a = new int;) unless they really need to be. It makes the code much harder to read, and if anyone has to maintain your code they'll call you an a-hole.
Second, int** ippArray = new int*[*a]; combined with multiple spots where you do this... for (int i = 1; i < *a+1; ++i) are bad. ippArray has valid references from 0 to *a, therefore it should be for (int i = 0; i < *a; ++i)
Edit: Try something like this http://ideone.com/4egQl3
Edit2: Also the standard advice...
{
std::vector<string> advice;
advice.push_back( "These will make your life easier" );
}
// No de-allocation needed!
Parts of your program that have undefined behaviour
Use of *b before you assign to it
Access out-of-bounds elements of all your arrays
Never initialise sum
Use of *sum before you assign to it
cleaned up, your code becomes
int main()
{
using namespace std;
int sum, a, b;
cout << "Total number of equips: ";
cin >> a;
typedef vector<vector<int> > vvint;
typedef vector<int> vint;
// Allocate a two-dimensional structure of ints
vvint ippArray(a);
// fill the array
for (vvint::size_t i = 0; i < a; ++i) {
cout << "Total number of catches for " << i+1 << "th equip : ";
cin >> b;
cout << "Equip number: " << i+1 << endl;
ippArray[i] = vint(b);
for (int j = 0; j < b; ++j) {
cout << "Catch number: " << j+1 << endl;
cin >> ippArray[i][j];
}
}
// Output the array
for (const vint & inner : ippArray) {
for (int num : inner) {
cout << num << " ";
sum += num;
}
cout << endl;
}
cout << endl;
cout << "All catches of the all equipes: " << sum;
cin.get();
return 0;
}
My program should fill up and show an array. It should also calculate average value in the array.
The program stops at this line:
cin >> *f1[j];
I think it's the problem line, but I could have made mistakes elsewhere.
#include <iostream>
using namespace std;
// prototypes
void add(int*f[],int h);
void show(int*f[],int h);
int average(int*f[],int h);
int main()
{
// getting size of a array
cout << "How many numbers would you insert? : ";
int i = 0;
cin >> i;
cout << endl;
// the dinamic array
int * arr = new int[i];
// call functions
add(&arr, i);
show(&arr, i);
average(&arr, i);
// deleting the dinamic array
delete[] arr;
system("pause");
return 0;
}
// declaring of the functions
// this function should fill up the array
void add(int* f1[], int h)
{
for(int j = 0 ; j < h ; j++)
{
cout << "Insert " << j+1 << ". value : ";
cin >> *f1[j]; //this should be the problem
cout << endl;
}
}
// this function should show the array
void show(int *f2[], int h)
{
for(int j = 0 ; j < h ; j++)
{
cout << *f2[j] << ", ";
}
}
// this function should should show average value of the array
int average(int *f3[], int h)
{
int n = 0;
for(int j = 0 ; j < h ; j++)
{
n += *f3[j];
}
n /= h;
return n;
}
You aren't referencing your arrays correctly. p* points to index p[0]
cout << *f2[j] << ", ";
should be
cout << f2[j] << ", ";
It compiles and runs with the edits I made.
http://ideone.com/DsxOOP
Also, You aren't taking any inputs.
You'll need to:
use int* fX in your function signatures
drop the & referencing from your function calls (you already have a memory address stored in arr and there's no such thing as a memory address for another memory address)
not use * dereferencing within your functions (you're already dereferencing the array with [] indexing)
http://pastebin.com/xY7A6JvE compiles and runs.
Hey so I want to create n arrays (based off user input) of size x (also off user input). The way I was thinking of doing it was having a for loop perform n iterations and inside the loop ask the user for x. The problem is I'm not sure how to name the array using the variable n, I was thinking something like:
cout << "Enter n: ";
cin >> n
for (i = 0; i < n; i++)
{
cout << "Enter x: ";
cin >> x;
double*array+i;
array+i = new double[x]
}
To sum up my question is: can you create/name an array using a variable in C++?
Unfortunately, you can't do this in C++. Try something like this...
std::cout << "Enter n: ";
std::cin >> n
std::vector<std::vector<double> > arrays(n);
for (std::size_t i = 0; i < n; i++)
{
std::cout << "Enter x: ";
std::cin >> x;
arrays[i].reserve(x);
}
reserve only allocates, but does not construct the objects in the std::vector; if you want to construct them too, use resize.
PS Never use using namespace std; it makes your code harder to read and debug.
Since you are programming in C++, you should use STL containers (especially std::vector) instead of C-style arrays.
If you need to access an array by using the string that has been created in runtime, then you could use std::map< std::string, std::vector<double> >, which is pretty crazy idea though:
typedef std::vector<double> MyVector;
std::map<std::string, MyVector> myVectors;
// create an array:
std::string arrayName;
arrayName = std::string("someArray"); // could be: std::cin >> arrayName;
myVectors[arrayName] = MyVector(10, 1.23); // new vector of size 10
std::cout << myVectors["someArray"][4]; // prints 1.23
I'm not sure what exactly is what you are trying to achieve, but there are most likely more appropriate solutions. Is it really necessary to access these arrays via their names? I'm pretty sure that common std::vector< std::vector<double> > would suffice here.
Here's 3 solutions: the first is closest to your example code, the second is an improvement in order to be able to correctly retrieve the array elements within bounds, and the third is the reason why you are better served with vectors.
Solution 1:
It looks like you want your arrays to have names that are distinguishable by your loop iterator. Like Joe said, you could have an array of an array, so the inner arrays will be named array[0], array[1], ..., array[n - 1]. This will be achieved by using a pointer to pointer to double. Each of the inner pointers will be used to dynamically allocate arrays of double. Don't forget to delete the dynamically allocated memory.
#include <iostream>
int main()
{
unsigned int n;
std::cout << "Enter number of arrays: ";
std::cin >> n;
double** array = new double*[n];
for (int i = 0; i < n; ++i)
{
unsigned int size;
std::cout << "Enter size of array " << i << ": ";
std::cin >> size;
array[i] = new double[size];
for (int j = 0; j < size; ++j)
{
int element;
std::cout << "Enter element " << j << " of array " << i << ": ";
std::cin >> element;
array[i][j] = element;
}
}
for (int i = 0; i < n; ++i)
{
delete [] array[i];
}
delete[] array;
return 0;
}
Solution 2:
However, with the above code, you will have trouble accessing the elements of each inner array. Unless you memorized the size of each inner array you create with this, you might access something out of bounds. Therefore, an update to this code would be to add yet another array, let's call it sizeOfInnerArrays, where each of its element i keeps track of the size of inner array array[i]. Here's the update:
#include <iostream>
int main()
{
unsigned int n;
std::cout << "Enter number of arrays: ";
std::cin >> n;
double** array = new double*[n];
unsigned int* sizeOfInnerArrays = new unsigned int[n];
for (int i = 0; i < n; ++i)
{
std::cout << "Enter size of array " << i << ": ";
std::cin >> sizeOfInnerArrays[i];
array[i] = new double[sizeOfInnerArrays[i]];
for (int j = 0; j < sizeOfInnerArrays[i]; ++j)
{
int element;
std::cout << "Enter element " << j << " of array " << i << ": ";
std::cin >> element;
array[i][j] = element;
}
}
//prints out each array as curly-brace enclosed sets of doubles
for (int i = 0; i < n; ++i)
{
std::cout << "{";
for (int j = 0; j < sizeOfInnerArrays[i] - 1; ++j)
{
std::cout << array[i][j] << ", ";
}
std::cout << array[i][sizeOfInnerArrays[i] - 1] << "}" << std::endl;
}
// free dynamically allocated memory
for (int i = 0; i < n; ++i)
{
delete [] array[i];
}
delete[] array;
delete[] sizeOfInnerArrays;
return 0;
}
Solution 3:
However, that is too complicated, so you are better off using a container, like vector, as Joe suggested, whose data member keeps track of its size.
#include <iostream>
#include <vector>
int main()
{
unsigned int n;
std::cout << "Enter number of vectors: ";
std::cin >> n;
std::vector<std::vector<double> > myVec;
// ^ space between closing angle brackets not needed
// if using C++11 conforming compiler
for (int i = 0; i < n; ++i)
{
unsigned int size;
std::cout << "Enter size of vector " << i << ": ";
std::cin >> size;
std::vector<double> temp;
temp.reserve(size);
for (int j = 0; j < size; ++j)
{
double value;
std::cout << "Enter next value of vector " << i << ": ";
std::cin >> value;
temp.push_back(value);
}
myVec.push_back(temp);
}
for (int i = 0; i < myVec.size(); ++i)
{
std::cout << "{";
for (int j = 0; j < myVec.at(i).size() - 1; ++j)
{
std::cout << myVec.at(i).at(j) << ", ";
}
std::cout << myVec.at(i).back() << "}" << std::endl;
}
return 0;
}