I'm making a program for Dynamic Array, Where I implemented three methods. push_back(arguments...),pop_back(arguments...) and printArray(arguments...).
But when I increase the size of the array it gives the garbage value at that index and if I run the code for more than 15 values it stop working.
#include<iostream>
using namespace std;
void push_back(unsigned int value,unsigned int *array,int &arraySize,int &totalArrayItems ){
if(arraySize>totalArrayItems){
array[totalArrayItems]=value;
totalArrayItems=totalArrayItems+1;
cout<<"Current size: "<<arraySize<<endl;
}
else if(arraySize==totalArrayItems){
cout<<"Adding the Size of Array... \n";
unsigned int *tempArray=new unsigned int[arraySize+5];//making new array as asked in requirements
for(int i=0;i<arraySize;i++){
tempArray[i]=array[i];
cout<<"Value in Temp : "<<tempArray[i]<<endl;
}
unsigned int *temp=array;
array=tempArray;
arraySize=arraySize+5;
cout<<"Saving "<<value<<" at Position: "<<totalArrayItems<<endl;
array[totalArrayItems]=value;//adding the new value
cout<<"Value in Temp "<<totalArrayItems<<" : "<<tempArray[totalArrayItems]<<endl;
totalArrayItems=totalArrayItems+1;
cout<<"Updated size: "<<arraySize<<"Current value: "<<value<<endl;
delete []temp;//delete old array
}
}
void pop_back(unsigned int *array,int &arraySize,int &totalArrayItems){
if(totalArrayItems>0){
totalArrayItems=totalArrayItems-1;
if(totalArrayItems<(arraySize-5)){
unsigned int *tempArray=new unsigned int[arraySize-5];
for(int i=0;i <= totalArrayItems;i++){
tempArray[i]=array[i];
}
unsigned int *temp=array;
array=tempArray;
delete[] temp;
arraySize=arraySize-5;
}
}
}
void printArray(unsigned int *array,int totalArrayItems){
for(int i=0;i<totalArrayItems;i++){
cout<<"Value at "<<i<<" : "<<array[i]<<endl;
}
}
unsigned int* array in push_back is a local variable. When you assign a new value to it (a new pointer to a new memory location), it doesn't update the value of array in whatever method you called it from.
Pass a pointer to int* instead: int**, if you want your reallocations to stick.
Related
While learning the dynamic object creation in C++ i have encountered a doubt . Here is my code.
And my question is , when the limiting condition in the loop is same as that of the no of objects created it works fine. But what happens when the loop works for more than the size given , it seems printing the values entered , but we have created only 4 objects and changed the condition of loop to more than 4
#include <iostream>
using namespace std;
class item{
int number;
public:
item(){
cout<<"Constructor"<<endl;
}
~item(){
cout<<"Destructor"<<endl;
}
void get_num(int num){
number = num
};
void show_num(){
cout<<"Number is "<<number<<endl;
}
};
const int size=4;
int main() {
item *itemObj = new item[size];
item *d = itemObj; //copy the address of itemObj inorder to access its member functions later
int tempNum;
for (int i = 0; i < size; ++i) {
cout<<"Enter the Number"<<endl;
cin>>tempNum;
itemObj->get_num(tempNum);
itemObj++;
}
//to print the numbers entered
for (int i = 0; i < size; ++i) {
d->show_data();
d++;
cout<<d<<endl;
}
delete itemObj;
return 0;
}
Your code isn't working fine at all. Because you change the value of the pointer that you requested from the new operator. When you call the delete for the itemObj at the last line, it doesn't have its original value.
So, instead of modifying the itemObj, you should modify the copy of it which is the pointer d here. Therefore, the problem isn't about the iteration amount of the loop. It's actually the violation on the heap memory.
Also, if you're creating a dynamic array, you should call delete [] instead of delete.
Following codes are my own API for index prior queue.When I test insert function,I get wrong answer.Then I debug codes,I found that the value of array qp changed after executing sentence----item[k]=vwhich is in insert function.Why the value of array qp changed after assigning value to array item?
template <class T>
class IndexPriorQueue{
private:
int index;//the num of items
int size;//capacity
int* pq;//index binaryheap
int* qp;//qp[pq[i]]=pq[qp[i]]=i
T* item;//item array;
public:
IndexPriorQueue(int qsize){//constructor function
size=qsize;
index=0;
pq=new int(size+1);
qp=new int(size+1);
item=new T(size+1);
for(int i=0;i<size+1;i++)
qp[i]=-1;
}
void insert(int k,T v){
if(contain(k)){
cout<<"index is already in queue"<<endl;
return;
}
//cout<<"insert"<<endl;
item[k]=v;//debug,after excuting this sentence,the value of qp exchanged??
pq[++index]=k;
qp[k]=index;
swim(index);
}
bool contain(int k){
return qp[k]!=-1?1:0;
}
void swim(int j){
while(j>1){
if(item[pq[j/2]]<item[pq[j]]){
exch(j/2,j);
j=j/2;
}else{
break;
}
}
}
void exch(int m,int n){
int temp=pq[m];
pq[m]=pq[n];
pq[n]=temp;
qp[pq[m]]=m;
qp[pq[n]]=n;
}
void display(){
cout<<"item:";
for(int i=1;i<size+1;i++){
cout<<item[i]<<" ";
}
cout<<endl;
cout<<"pq:";
for(int i=1;i<size+1;i++){
cout<<pq[i]<<" ";
}
cout<<endl;
cout<<"qp:";
for(int i=1;i<size+1;i++){
cout<<qp[i]<<" ";
}
cout<<endl;
}
};
Following codes are main function
int main(){
cout<<"before insert:"<<endl;
IndexPriorQueue<char> ipq(10);
ipq.display();
ipq.insert(1,'a');
cout<<"after insert:"<<endl;
ipq.display();
return 0;
}
The problems is your allocations. Take for example
new T(size+1)
That allocates one object of type T and initializes it to the value size + 1 (i.e. it calls the T constructor with size + 1).
If you need to allocate an "array" you should use square brackets [] as in
new T[size+1]
That will allocate an array of size + 1 number of T objects.
A much better solution though, is to use std::vector instead of doing it all manually yourself.
I want to add X to the end of my Array if the array is full I double the size but i'm having trouble inserting it into newArray after I get it into newArray I use pointers to switch dynamicArray to newArray.
#include <iostream>
using namespace std;
class IntegerDynamicArray {
public:
IntegerDynamicArray();
~IntegerDynamicArray();
int add(int x);
private:
int * dynamicArray;
int currentSize=maxSize;
int maxSize=4;
};``
IntegerDynamicArray::IntegerDynamicArray()
{
dynamicArray = new int [maxSize];
}
IntegerDynamicArray::~IntegerDynamicArray()
{
delete [] dynamicArray;
}
int IntegerDynamicArray::add(int x)
{
cout<<x<<endl;
if(dynamicArray[currentSize-1]!=0)
{
int * newArray;
newArray= new int[currentSize*2];
for(int i =0;i<currentSize;i++)
{
newArray[i]=dynamicArray[i];
newArray[currentSize]=x;
}
currentSize=currentSize*2;
dynamicArray = newArray;
}
else
{
int * newArray;
newArray= new int[currentSize];
for(int i =0;i<currentSize;i++)
{
newArray[i]=dynamicArray[i];
newArray[currentSize-1]=x;
}
dynamicArray = newArray;
}
return *dynamicArray;
}
int main() {
IntegerDynamicArray intDynArray;
while (1) {
char input;
cout << "Enter A for add or anything else to quit: ";
cin >> input;
if (input == 'A') {
cout << "Enter number to add: ";
int x;
cin >> x;
cout << intDynArray.add(x) << endl;
} else {
break;
}
}
}
There are several problems with your code. Because you didn't asked a dedicated question these are the main ones:
Your class lacks a variable containing the index of the last written (or next free) index of the array. Instead you (mis)use currentSize as such index variable.
On each call of add() you allocate a new array although it might not be full already.
As already mentioned in the comments you do not delete [] your old arrays after copying into the new one.
You use 0 as indicator that a slot in your array is empty, but you do not prevent adding 0 as regular element and you do not initialize your array to zero.
As Thomas Matthews pointed out:
You are leaking memory while calling add(int x). For each use of new, there should be a call for delete
Consider the following:
int n=10;
int* x= new int[n];
//assign some values
int* temp=new int[n*2]; //create new array
for(int i=0;i<n;i++)
temp[i]=x[i]; //assign values from x
delete[] x; //free memory
x=temp; //assign to x address of new array
Manual memory managment can be risky, so consider using std::vector in future
I tried to "select sort" an array. But instead of displaying the original array with just a "for loop", to go beyond the normal way and implement the stuffs I learned I decided to pass the original array to a function called "org_array" and tried to invoke it in the "void main()". But got couple of errors. I can't figure out what's the error I made in passing the parameters. Help please?
Code:
#include<iostream>
#include<conio.h>
using namespace std;
extern int s;
void org_array(int arr[30],int y);
void main()
{
int i,n,j,pos,a[30];
cout<<"Enter n: "<<endl;
cin>>n;
cout<<"\nEnter array: "<<endl;
for(i=0;i<n;i++){
cin>>a[i];
}
cout<<"Orginal Array: ";
org_array(a[30],n);
/*for(i=0;i<n;i++){
cout<<a[i]<<" | ";
}*/
for(i=0;i<n-1;i++)
{
int small=a[i];
pos=i;
for(j=i+1;j<n;j++)
{
if(a[j]<small)
{
small=a[j];
pos=j;
}
}
int temp=a[i];
a[i]=a[pos];
a[pos]=temp;
}
cout<<"\tSorted Array: ";
for(i=0;i<n;i++){
cout<<a[i]<<" | ";
}
getch();
}
void org_array(int arr[30],int y){
for(s=0;s<y;s++)
{
cout<<" "<<arr[s];
}
}
org_array(a[30],n);
is incorrect. It should be:
org_array(a,n);
And main should return int as per ISO. Further your declarations and definitions respectively should be this way:
void org_array(int [],int); // declaration - removed 30 since we might want to pass an array of larger size
void org_array(int arr[],int y) //definition
{
for(int s=0;s<y;s++) // You did not declare s as int
{
cout<<" "<<arr[s];
}
}
Just a side note:
An lvalue [see question 2.5] of type array-of-T which appears in an expression decays (with three exceptions) into a pointer to its first element; the type of the resultant pointer is pointer-to-T because an array is not a "modifiable lvalue,"
(The exceptions are when the array is the operand of a sizeof or & operator, or is a literal string initializer for a character array.)
In your code:
cout<<"Orginal Array: ";
org_array(a[30],n);
Should pass just the name of array as argument. Arrays are passed as reference to address of block of memory. You are referring to a specific index in array in your call. http://www.cplusplus.com/doc/tutorial/arrays/
org_array(a,n);
In your code:
void org_array(int arr[30],int y){
for(s=0;s<y;s++)
{
cout<<" "<<arr[s];
}
}
for loop requires a type for variable s. I assume you want an integer.
for(int s=0; s<y; s++)
Your main function should also be of type int and return int value.
I'm trying to create an application in C++. In the application I have the default constructor and another constructor with 3 arguments.
The user is providing from the keyboard an integer that it will be used to create an array of objects using the non default constructor.
Unfortunately I haven't been able to finish it till now, since I'm having issues with the creation of the array of objects that they will use the non default constructor.
Any suggestions or help?
#include<iostream>
#include<cstring>
#include<cstdlib>
#include <sstream>
using namespace std;
class Station{
public:
Station();
Station(int c, char *ad, float a[]);
~Station();
void setAddress(char * addr){
char* a;
a = (char *)(malloc(sizeof(addr+1)));
strcpy(a,addr);
this->address = a;
}
void setCode(int c){
code=c;
}
char getAddress(){
return *address;
}
int getCode(){
return code;
}
float getTotalAmount(){
float totalAmount=0;
for(int i=0;i<4;i++){
totalAmount+=amount[i];
}
return totalAmount;
}
void print(){
cout<<"Code:"<<code<<endl;
cout<<"Address:"<<address<<endl;
cout<<"Total Amount:"<<getTotalAmount()<<endl;
cout<<endl;
}
private:
int code;
char *address;
float amount[4];
};
Station::Station(){
code= 1;
setAddress("NO ADDRESS GIVEN");
amount[0]= 0.0;
amount[1]= 0.0;
amount[2]= 0.0;
amount[3]= 0.0;
}
Station::Station(int c, char *ad, float a[]){
if( (c>=1&& c<=10 ) ){
code=c;
address=ad;
for(int i=0;i<4;i++){
amount[i]=a[i];
}
}else{
code= 1;
setAddress("NO ADDRESS GIVEN");
amount[0]= 0.0;
amount[1]= 0.0;
amount[2]= 0.0;
amount[3]= 0.0;
}
}
Station::~Station(){
}
int main(){
int size,code;
char *addrr;
addrr = (char *)(malloc(sizeof(addrr+1)));
float mes[4];
do{
cout<<"size of array:";
cin>>size;
}while(size<=0 || size>=11);
// Station *stations= new Station[size];
// Station** stations = new Station*[size];
Station stations[size];
for(int i=0;i<size;i++){
cout<<"code:";
cin>>code;
cout<<"address:";
cin>>addrr;
double amo=0;
for(int k=0;k<4;k++){
cout<<"values"<<k+1<<":";
cin>>mes[k];
}
}
/*
for(int q=0;q<size;q++){
stations[q].print();
}
*/
return 0;
}
the values that I'll take from cin I want to assign them to the objects of the array!
You can either create the array default-initialized and then fill the array with the wanted object:
foo arr[10];
std::fill(arr, arr+10, foo(some, params));
Alternatively you could use std::vector and do just:
std::vector<foo> arr(10, foo(some, params));
In C++0x, you can use braced-init-list in new expression, which means you can do this:
#include <iostream>
class A
{
public:
A(int i, int j){std::cout<<i<<" "<<j<<'\n';}
};
int main(int argc, char ** argv)
{
int *n = new int[3]{1,2,3};
A *a = new A[3]{{1,2},{3,4},{5,6}};
delete[] a;
delete[] n;
return 0;
}
Compiled under g++ 4.5.2, using g++ -Wall -std=c++0x -pedantic
Since you say you can't use std::string, this is going to be much more difficult. The line addrr = (char *)(malloc(sizeof(addrr+1))); is not doing what you think it is. Instead of using malloc to allocate on the heap and since there is no free (which will lead to a memory leak), it will be much easier if we allocate on the stack with a predetermined buffer size: char addrr[BUFFER_LENGTH]. With BUFFER_LENGTH defined before Station's declaration as const int BUFFER_LENGTH = 20; or some other appropriate length.
To use the non-default constructor, adding stations[i] = Station(c, addrr, mes); at the end of the for loop will do the trick.
for(int i=0;i<size;i++){
cout<<"code:";
cin>>code;
cout<<"address:";
cin>>addrr; // do not read in strings longer than 20 characters or increase BUFFER_LENGTH’s size
double amo=0;
for(int k=0;k<4;k++){
cout<<"values"<<k+1<<":";
cin>>mes[k];
}
stations[i] = Station(c, addrr, mes);
}
But, this is not going to work properly since the constructor is copying the addrr pointer, not the data. I would recommend also changing the data member char *address to char address[BUFFER_LENGTH]. Then, in the constructor you can replace the line address=ad; with strcpy(address, ad);.
Note: setAddress and getAddress will now need to be updated.
Another line that is troubling is Station stations[size];. This is non-standard since size is not a known at compile time. Either use Station *stations= new Station[size]; and remember to delete or if you can use a std::vector, use std::vector<Station> stations(size);
If you do go the std::vector route, using push_back will work nicely:
std::vector<Station> stations;
for(int i=0;i<size;i++){
cout<<"code:";
cin>>code;
cout<<"address:";
cin>>addrr;
double amo=0;
for(int k=0;k<4;k++){
cout<<"values"<<k+1<<":";
cin>>mes[k];
}
stations.push_back( Station(c, addrr, mes) );
}