Re: problem understanding a functionality of constructor. - C / C++ / MFC Discussion Boards

Re: error C2143: syntax error: missing ':' before 'constant'

ForNow28-Mar-18 14:50

ForNow

28-Mar-18 14:50

C++

typedef USN_RECORD_V2 USN_RECORD, *PUSN_RECORD;

C++

typedef struct {

    DWORD RecordLength;
    WORD   MajorVersion;
    WORD   MinorVersion;
    FILE_ID_128 FileReferenceNumber;
    FILE_ID_128 ParentFileReferenceNumber;
    USN Usn;
    LARGE_INTEGER TimeStamp;
    DWORD Reason;
    DWORD SourceInfo;
    DWORD SecurityId;
    DWORD FileAttributes;
    WORD   FileNameLength;
    WORD   FileNameOffset;
    WCHAR FileName[1];

} USN_RECORD_V3, *PUSN_RECORD_V3;

C++

ypedef struct {
    USN_RECORD_COMMON_HEADER Header;
    FILE_ID_128 FileReferenceNumber;
    FILE_ID_128 ParentFileReferenceNumber;
    USN Usn;
    DWORD Reason;
    DWORD SourceInfo;
    DWORD RemainingExtents;
    WORD   NumberOfExtents;
    WORD   ExtentSize;
    USN_RECORD_EXTENT Extents[1];
} USN_RECORD_V4, *PUSN_RECORD_V4;

Re: error C2143: syntax error: missing ':' before 'constant'

Victor Nijegorodov27-Mar-18 21:18

Victor Nijegorodov

27-Mar-18 21:18

ForNow wrote:
C2143 syntax error missing ':' before constant the error might make sense if
C++
USN_RECORD_COMMON_HEADER 
wasn't defined but it is a few lines above

Could you post these "few lines"?

Re: error C2143: syntax error: missing ':' before 'constant'

ForNow28-Mar-18 0:31

ForNow

28-Mar-18 0:31

Here is the definition USN_RECORD_COMMON_HEADER

typedef struct {
    DWORD RecordLength;
    WORD   MajorVersion;
    WORD   MinorVersion;
} USN_RECORD_COMMON_HEADER, *PUSN_RECORD_COMMON_HEADER;

Re: error C2143: syntax error: missing ':' before 'constant'

Richard MacCutchan27-Mar-18 22:08

Richard MacCutchan

27-Mar-18 22:08

Have a look in Winioctl.h to check the definitions of these types. My version compiles them fine on VS2017 and Windows 10.

Re: error C2143: syntax error: missing ':' before 'constant'

Jochen Arndt27-Mar-18 22:41

Jochen Arndt

27-Mar-18 22:41

Check the typedefs of the three structures that fail for mutual non standard members.

A candidate is the USN member.

Do you have a define directive using the same name anywhere in your project?

If that does not help enable the creation of preprocessor output files. Then you can check what the compiler "sees".

Re: error C2143: syntax error: missing ':' before 'constant' The Hercules makefile has V1,V2,V3,V4

ForNow28-Mar-18 15:44

ForNow

28-Mar-18 15:44

THANKS

problem understanding a functionality of constructor.

Tarun Jha27-Mar-18 4:39

Tarun Jha

27-Mar-18 4:39

i was going through a article about friend function and then in i came across this code:

#include <iostream>
using namespace std;

class Distance
{
    private:
        int meter;
    public:
        Distance(): meter(0) { }
        //friend function
        friend int addFive(Distance);
};

// friend function definition
int addFive(Distance d)
{
    //accessing private data from non-member function
    d.meter += 5;
    return d.meter;
}

int main()
{
    Distance D;
    cout<<"Distance: "<< addFive(D);
    return 0;
}

in the above code what is

Quote:
Distance(): meter(0) { }

and how is a object of class distance is able to access a private member ?

Quote:
int addFive(Distance d)
{
//accessing private data from non-member function
d.meter += 5;
return d.meter;
}

Thank you.

Re: problem understanding a functionality of constructor.

Jochen Arndt27-Mar-18 4:55

Jochen Arndt

27-Mar-18 4:55

The first uses the expression list of the constructor to initialise a member by passing to the member's constructor. See Constructors and member initializer lists - cppreference.com[^] for the various possible methods about member initialisation besides assigning in the compound statement (the final block enclosed by braces).

The access to private and protected members is granted by the friend declaration - cppreference.com[^].

Re: problem understanding a functionality of constructor.

Richard MacCutchan27-Mar-18 5:18

Richard MacCutchan

27-Mar-18 5:18

You should get hold of a good C++ book. Probably the best would be the one written by Bjarne Stroustrup[^]

Re: problem understanding a functionality of constructor.

CPallini27-Mar-18 5:36

CPallini

27-Mar-18 5:36

Welcome to C++. Big Grin | :-D

I mean:

constructors are the very basics of an OOP language (you must be sure to grasp them before even attempting to code).
accessing an otherwise unaccessible member is the very purpose of the friend declaration.

Hackerrank:Down to Zero problem

SrinivasaRamanujan25-Mar-18 10:23

SrinivasaRamanujan

25-Mar-18 10:23

Problem statement: You are given Q queries. Each query consists of a single number N. You can perform any of the 2 operations on in each move:

1: If we take 2 integers a and b where N=aXb(a!=1,b!=1) then we can change N=max(a,b).

2: Decrease the value of N by 1. Determine the minimum number of moves required to reduce the value of N to 0

Input Format

The first line contains the integer Q.

The next Q lines each contain an integer,N .

Output Format

Output Q lines. Each line containing the minimum number of moves required to reduce the value of N to 0.

Sample Input

2

3

4

Sample Output

3

3

Explanation

For test case 1, We only have one option that gives the minimum number of moves. Follow 3->2 -> 1->0 .

Hence, 3 moves.

For the case 2, we can either go 4->3 ->2 ->1 ->0 or4 -> 2-> 1->0 . The 2nd option is more optimal. Hence, 3 moves.

My algo:

if a number is N then

I do looping until sqrt(N) to find if it is a prime or not.
if it is a prime number then N=N-1
if it not a prime number,one of the largest factor(say a) is <=sqrt(N) then other will be b=N/a now b>a then put N=b;
increment count(pass by value).
then next iteration for N ,until it is greater than 1.
return count.

algorithms works fine with small value but predicts less optimal solution for large values.why?

Re: Hackerrank:Down to Zero problem

David Crow25-Mar-18 15:41

David Crow

25-Mar-18 15:41

See here.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

In type conversion of 2 different classes can i convert both ways ?

Tarun Jha25-Mar-18 5:14

Tarun Jha

25-Mar-18 5:14

i want to make a program that can convert from class a type to class b & vice versa..
i already made a program that does one type of conversion..

//define 2 classes polar & rectangle to represent points int the polar & rectanglular system.
#include <iostream>
#include <cmath>
using namespace std;

class Polar;

//====================================================
class Rectangle{
    float length, bredth;
public:
    Rectangle(){}
    Rectangle(float ,float);

    /*
      operator Polar(){
        Polar temp;
        float a = atan(length/bredth), r = sqrt(x*x + y*y);
        temp.getAngle(a);
        temp.getRadius(r);

        return(temp);
    }
    */

    int getLength(){return(length);}
    int getBredth(){return(bredth);}
    void putLength(float x){length = x;}
    void putBredth(float y){bredth = y;}

    void putData(){cout<<"Length : "<<length<<"\tBreadth : "<<bredth<<endl;}
    ~Rectangle(){}
};

Rectangle::Rectangle(float x, float y){
    length = x;
    bredth = y;
}

//====================================================

class Polar{
    float angle, rad;
public:

    Polar(){}
    Polar(float , float);

    operator Rectangle(){
        Rectangle temp;
        float l = rad*cos(angle), b =rad*sin(angle) ;
        temp.putLength(l);
        temp.putBredth(b);

        return(temp);
    }

    int getAngle(){return(angle);}
    int getRadius(){return(rad);}
    void putData(){cout<<"Angle : "<<angle<<"\tRadius : "<<rad<<endl;}
    ~Polar(){}
};

Polar::Polar(float x, float y){
    angle = x;
    rad = y;
}

// Rectangle::operator Polar(){
//     Polar temp;
//     float a = atan(length/bredth), r = sqrt(x*x + y*y);
//     temp.getAngle(a);
//     temp.getRadius(r);
//
//     return(temp);
// }
//===========================================================

int main(){
    Rectangle r1(40, 20.23);
    Polar p1(120, 25);

    r1 = p1;
    r1.putData();

    //p1 = r1;
    //p1.putData();

    return 0;

}

as in the above code i have converted class Polar to class Rectangle, but i also want to have a conversion of class Rectangle to class Polar.

Thank you

Re: In type conversion of 2 different classes can i convert both ways ?

Victor Nijegorodov25-Mar-18 8:07

Victor Nijegorodov

25-Mar-18 8:07

Tarun Jha wrote:
as in the above code i have converted class Polar to class Rectangle,

Did you test it?
Does it work?

I ask because I see neither the assignment operator

Rectangle& Rectangle::operator =(const Polar& polar)

nor the ctor to create Rectangle instance from the Polar one... Confused | :confused:

Re: In type conversion of 2 different classes can i convert both ways ?

Tarun Jha25-Mar-18 23:26

Tarun Jha

25-Mar-18 23:26

but i am not using any variables with reference to heap, so i thought it shouldn't be needed for ex:- new, *variable etc.

Re: In type conversion of 2 different classes can i convert both ways ?

CPallini25-Mar-18 10:50

CPallini

25-Mar-18 10:50

C++

#include <iostream>
#include <cmath>
using namespace std;

class Polar;

//====================================================
class Rectangle
{
  float length, bredth;
public:
  Rectangle(){}
  Rectangle(float ,float);

  operator Polar();

  int getLength(){return(length);}
  int getBredth(){return(bredth);}
  void putLength(float x){length = x;}
  void putBredth(float y){bredth = y;}

  void putData(){cout<<"Length : "<<length<<"\tBreadth : "<<bredth<<endl;}
  ~Rectangle(){}
};


//====================================================

class Polar{
  float angle, rad;
public:

  Polar(){}
  Polar(float , float);

  operator Rectangle();

  int getAngle(){return(angle);}
  int getRadius(){return(rad);}
  void putAngle(float a){angle=a;}
  void putRadius(float r){rad = r;}

  void putData(){cout<<"Angle : "<<angle<<"\tRadius : "<<rad<<endl;}
  ~Polar(){}
};

//===========================================================
Rectangle::Rectangle(float x, float y)
{
  length = x;
  bredth = y;
}

Rectangle::operator Polar()
{
  Polar temp;
  float a = atan2(bredth, length), r = sqrt(length*length + bredth*bredth);
  temp.putAngle(a);
  temp.putRadius(r);

  return(temp);
}

//===========================================================
Polar::Polar(float x, float y)
{
  angle = x;
  rad = y;
}
Polar::operator Rectangle()
{
  Rectangle temp;
  float l = rad*cos(angle), b =rad*sin(angle);
  temp.putLength(l);
  temp.putBredth(b);
  return(temp);
}

//===========================================================
int main()
{
  float radians = 120 * M_PI / 180; // convert to radians

  // roundtrip polar->rectangle->polar
  Polar p1(radians, 25);
  p1.putData();

  Rectangle r1 = p1;
  r1.putData();

  Polar p2 = r1;
  p2.putData();

  return 0;
}

Re: In type conversion of 2 different classes can i convert both ways ?

Tarun Jha25-Mar-18 23:25

Tarun Jha

25-Mar-18 23:25

thank you

Re: In type conversion of 2 different classes can i convert both ways ?

CPallini26-Mar-18 0:18

CPallini

26-Mar-18 0:18

You are welcome.

Adding two matrix objects and assigning the result to third object using overloaded operators ?

Tarun Jha24-Mar-18 8:19

Tarun Jha

24-Mar-18 8:19

here ih the code below i have tried to add two matrix objects and assign it to the third object but it doesn't give expected result and the rather some garbage value.

include <iostream>
using namespace std;

class matrix{
    int **p;    //pointer to Matrix
    int d1, d2;

public:
    //matrix(){}                  //default constructor
    matrix(int x=20, int y=20);       //parameterised

    void get_element();
    void put_element();
    int checkAdd(matrix &);                                     //to check the feasibility of the operation

    //Rule of three
    matrix operator + (matrix &);
    void operator = (matrix );

    ~matrix(){
        for (int i = 0; i < d1; i++)
            delete p[i];
        delete p;
    }
};

matrix temp;                    //global matrix temp

//=============================================

void matrix::operator = (matrix obj){

    this->d1 = obj.d1;
    this->d2 = obj.d2;
    for(int i=0; i<d1; i++)
        for(int j=0; j<d2; j++)
            this->p[i][j] = obj.p[i][j];

    //put_element();
    //return(*this);
}

matrix matrix::operator+(matrix &obj){
    if(checkAdd(obj)==0)
    {
        //matrix temp;
        for(int i=0; i<obj.d1; i++)
            for(int j=0; j<obj.d2; j++)
                temp.p[i][j] = this->p[i][j] + obj.p[i][j];


        //temp.put_element();
        return(temp) ;
    }

    cout<<"coloumn and rows of both matrix are not equal !"<<endl;
    return (*this);
}

matrix ::matrix(int x, int y)
{
    d1 = x;
    d2 = y;
    p = new int *[d1];                  //creates an array of pointers

    for(int i=0; i<d1; i++)
        p[i] = new int [d2];            //creates row for each row
}

int matrix::checkAdd(matrix &obj){
    if((this->d1 == obj.d1) && (this->d2 == obj.d2))
        return 0;
    else return 1;
}

void matrix::get_element(){
    for(int i=0; i<d1; i++)
        for(int j=0; j<d2; j++){
            cout<<"m["<<i<<"]["<<j<<"] = ";
            cin>>p[i][j];
        }
    //cout<<"Following is your Matrix : \n\n";
    //put_element();
}

void matrix::put_element(){
    cout<<"\n\n";
    for(int i=0; i<d1; i++){
        for(int j=0; j<d2; j++){
            cout<<p[i][j]<<"\t";
        }
        cout<<endl;
    }

}

//=============================================

int main(){
    matrix A(3, 2), B(3, 2), C;                     //matrix objects a constucted

    cout<<"Enter matrix elements row by row \n\n";
    A.get_element();
    A.put_element();

    B.get_element();
    B.put_element();

    C = A + B;
    cout<<"\n\n";
    C.put_element();

    return 0;
}

thank you

Re: Adding two matrix objects and assigning the result to third object using overloaded operators ?

Victor Nijegorodov24-Mar-18 8:35

Victor Nijegorodov

24-Mar-18 8:35

What result did you expect and what did you get?

Re: Adding two matrix objects and assigning the result to third object using overloaded operators ?

Tarun Jha24-Mar-18 10:06

Tarun Jha

24-Mar-18 10:06

Quote:
So basically i want to add 2 matrix object and assign the result to the third non-initiated matrix object, without changing the values of first 2 original matrix.

this is the result i am getting.

Quote:
Enter matrix elements row by row

m[0][0] = 1
m[0][1] = 2
m[1][0] = 3
m[1][1] = 4
m[2][0] = 5
m[2][1] = 6

1 2
3 4
5 6
m[0][0] = 7
m[0][1] = 8
m[1][0] = 9
m[1][1] = 10
m[2][0] = 11
m[2][1] = 12

7 8
9 10
11 12

8 10 47120720 0 0 0 0 0 0 0 50331651 41272 47127056 0 47120720 0 0 2396 136 0
12 14 47120720 0 1550742898 1148219457 1549890657 1633906508 1700027500
1426092141 1146242387 1229016399 1162100046 1330924371 1429482832 844253517 1398079566 1329877573 1313423693 1095717471
16 18 47120720 0 1162690894 1918981181 1426091637 1347568979 1229344594
1128088908 1934974010 1551069797 1970430292 1398145134 1127232561 1414417743 1397509967 1547322173 1735357008 544039282
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
47120720 0 47127424 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

i want a result:
8 10
12 14
16 18

Re: Adding two matrix objects and assigning the result to third object using overloaded operators ?

Richard MacCutchan24-Mar-18 21:13

Richard MacCutchan

24-Mar-18 21:13

You already posted this exact question in the ATL/STL forum, and I gave you a suggestion. If you google for "operator overload C++" you will find plenty of samples.

Re: Adding two matrix objects and assigning the result to third object using overloaded operators ?

Tarun Jha25-Mar-18 5:08

Tarun Jha

25-Mar-18 5:08

i was told that these type of questions are to be posted here.
and i did the program..

#include <iostream>
using namespace std;

class matrix{
    int **p;                        //pointer to Matrix
    int d1, d2;
    int id=0;                        //identif which operator is used

public:
    //matrix(){}                      //default constructor
    matrix(int x=20, int y=20);       //parameterised

    //to pass private data-members to other objects
    int getD_1(){return (d1);}
    int getD_2(){return (d2);}
    //int getId(const int x){id =x ;}
    //void showId(){cout<<"ID :\t"<<id<<endl;}

    //for taking input nad printing output
    void get_element();
    void put_element();

    //to check feasibility
    friend int checkAdd(matrix &, matrix &);                                     //to check the feasibility of the operation
    friend int checkMul(matrix &, matrix &);

    //Rule of three
    friend matrix operator+(matrix &, matrix &);
    friend matrix operator*(matrix &, matrix &);
    //friend matrix operator-(matrix &, matrix &);

    void operator = (matrix );

    ~matrix(){
        for (int i = 0; i < d1; i++)
            delete p[i];
        delete p;
    }
};

//=================================================================================================================

//defining overloaded assingment operator
void matrix::operator = (matrix obj){
    this->d1 = obj.d1;
    this->d2 = obj.d2;
    this->id = obj.id;
    for(int i=0; i<d1; i++)
        for(int j=0; j<d2; j++)
            this->p[i][j] = obj.p[i][j];
}

//defining overloaded addition operator
matrix operator+(matrix &a, matrix &b){
    matrix temp;
    temp.d1 = a.d1;
    temp.d2 = a.d2;
    temp.id = 1;

    if(checkAdd(a, b) == 0){                //checks the viability if it's feasible or not.
        for(int i=0; i<temp.d1; i++)
            for(int j=0; j<temp.d2; j++)
                temp.p[i][j] = a.p[i][j] + b.p[i][j] ;

        return(temp);
    }
    else {
        cout<<"Matrix addition not possible as rows and coloumn's of given 2 matrices are not equal"<<endl;
        return(a);
    }
}

//defining overloaded Multiplication operator
matrix operator*(matrix &a, matrix &b){
    matrix temp;
    temp.d1 = a.d1;
    temp.d2 = b.d2;
    temp.id = 2;

    if(checkMul(a, b) == 0){              //checks the viability if it's feasible or not.
        int sum=0;
        for (int c = 0; c < a.d1; c++) {
            for (int d = 0; d < b.d2; d++) {
                for (int k = 0; k <b.d1; k++) {
                    sum = sum + a.p[c][k]*b.p[k][d];
                }
                temp.p[c][d] = sum;
                sum = 0;
            }
        }
        return (temp);
    }
    else {
        cout<<"Matrix Multiplication is not possible as coloumn of 1st Matrix != Row of 2nd Matrix "<<endl;
        return(a);
    }
}

//defining parameterised constucter
matrix ::matrix(int x, int y){
    d1 = x;
    d2 = y;
    p = new int *[d1];                  //creates an array of pointers

    for(int i=0; i<d1; i++)
        p[i] = new int [d2];            //creates row for each row
}

//defining checkAdd f^n to check if given 2 matrices obj can be added or not
int checkAdd(matrix &a, matrix &b){
    if(a.getD_1() == b.getD_1() && a.getD_2() == b.getD_2())
        return 0;
    else return 1;
}

//defining checkMul f^n to check if 2 matrices obj can be Multiplied.
int checkMul(matrix &a, matrix &b){
    if(a.getD_2() == b.getD_1())
        return 0;
    else return 1;
}

//gets the element from the user.
void matrix::get_element(){
    for(int i=0; i<d1; i++)
        for(int j=0; j<d2; j++){
            cout<<"m["<<(i+1)<<"]["<<(j+1)<<"] = ";
            cin>>p[i][j];
        }
}


//displays the current matrix
void matrix::put_element(){
    if(id == 1) cout<<"\nThe result of addition of 2 matrices is :"<<endl;
    else if(id==2)  cout<<"\nThe result of product of 2 matrices is:"<<endl;

    for(int i=0; i<d1; i++){
        for(int j=0; j<d2; j++){
            cout<<p[i][j]<<"\t";
        }
        cout<<endl;
    }
    cout<<"\n";
}

//=====================================================================================================================

int main(){
    matrix A(3, 2), B(2, 4), C;                     //matrix objects a constucted

    cout<<"Enter matrix elements row by row \n\n";
    A.get_element();
    A.put_element();

    B.get_element();
    B.put_element();

    C = A * B;
    C.showId();
    C.put_element();

    C = A + B;
    C.showId();
    C.put_element();

    return 0;
}

and thank you for the advice

Re: Adding two matrix objects and assigning the result to third object using overloaded operators ?

Richard MacCutchan25-Mar-18 5:32

Richard MacCutchan

25-Mar-18 5:32

Forget about matrix calculations. You need to go and study operator overloading and get that working on a basic class first. Once you understand how to do it correctly so you get no errors, then you can move on to the matrix functions.

Re: Adding two matrix objects and assigning the result to third object using overloaded operators ?

Tarun Jha25-Mar-18 6:37

Tarun Jha

25-Mar-18 6:37

is there anything wrong with the program i have posted before ?

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