C++ Array passig parameters - c++

Question

I'm new in C++
I try to pass array as parameters I can't find a solution.
Here's my code :
My Header code
autobus.h
#ifndef autobus_H
#define autobus_H
#include <iostream>
using namespace std;
class autobus{
public :
int placeautobus[2] [40];
autobus();
void affichageTicket();
int calculdesplaces(int, int);
};
#endif
Bus.cpp
#include <iostream>
#include "autobus.h"
autobus::autobus(){
int i,j;
for (i=0;i<2;i++) {
for (j=0;j<40;j++)
placeautobus[i][j] = 0;
}
};
void autobus::affichageTicket()
{
}
int autobus::calculdesplaces(int typeautobus, int *placeautobus[2][40]){
int placenumero;
for (int place = 0; place < 40; place++){
if ( placeautobus[typeautobus][place] ==0) {
placenumero = place+1;
cout <<"Places : "<< placenumero <<endl;
}
}
return placenumero;
}
finally my main.cpp
#include <cstdlib>
#include <iostream>
#include "autobus.h"
using namespace std;
int main()
{
int TypeAutobus;
autobus *choixautobus = new autobus();
cout << "1 for smoking bus" << endl;
cout << "2 for non-smoking bus" << endl;
cin >> TypeAutobus;
choixautobus->calculdesplaces(TypeAutobus, choixautobus->placeautobus[2][40]);
system("PAUSE");
return EXIT_SUCCESS;
}
Everything works, but when I add this line in my main.cpp :
choixautobus->calculdesplaces(TypeAutobus, choixautobus->placeautobus[2][40]);
I have an error, I try many things.
I just want to call my function calculdesplaces with the variable : choixautobus having array placeautobus.
Can someone know how to do this.
thanks

Answer 1

Like others have said already, the code you have now shouldn't compile right now because of the declaration and definition mismatch for calculdesplaces.
You shouldn't need to pass the placeautobus array at all since it is a member of the autobus class. Just delete your 2nd argument from calculdesplaces and you should be able to do what you want.
int autobus::calculdesplaces(int typeautobus){
int placenumero;
for (int place = 0; place < 40; place++){
if ( placeautobus[typeautobus][place] ==0) {
placenumero = place+1;
cout <<"Places : "<< placenumero <<endl;
}
}
return placenumero;
}

Answer 2

In your class declaration, you need to specify the correct array pointer type for the second parameter of calculdesplaces():
class autobus{
public :
autobus();
void affichageTicket();
int calculdesplaces(int typeautobus, int (*placeautobus)[40]);
int placeautobus[2][40];
};
This declares, that you are passing a pointer to an array of 40 int elements. This is precisely the type to which the 2D array int placeautobus[2][40]; decays when you use its name: When you mention the name of an array, the array name decays into a pointer to its first element. In the case of an array of type int ()[2][40], that is a pointer to the first line array (type is int (*)[40]).
Note that the parentheses in int (*placeautobus)[40] are very important: the array subscript operator [] has a higher precedence than the dereferencing operator *, so int (*placeautobus)[40] means something very different from int* placeautobus[40].
I have also taken the liberty of including the variable names in the method declaration, this provides essential information to the reader, even though the compiler ignores it.
In the implementation of calculdesplaces(), you can access the argument array precisely the same way as you can access any 2D array:
int autobus::calculdesplaces(int typeautobus, int (*placeautobus)[40]) {
int placenumero;
for (int place = 0; place < 40; place++) {
if ( placeautobus[typeautobus][place] ==0) {
placenumero = place+1;
cout <<"Places : "<< placenumero <<endl;
}
}
return placenumero;
}
Now you can easily call your function by just passing the array:
int main() {
int TypeAutobus;
autobus *choixautobus = new autobus();
cout << "1 for smoking bus" << endl;
cout << "2 for non-smoking bus" << endl;
cin >> TypeAutobus;
choixautobus->calculdesplaces(TypeAutobus, choixautobus->placeautobus);
system("PAUSE");
return EXIT_SUCCESS;
}
Note:
The above only fixes the symptoms, not the disease. The actual problem is, that the design of the class itself is flawed. Data members should generally not be public, and methods should work on the data of the object on which they are called, instead of relying on getting parts of the object passed in via additional arguments. So, the class definition should look like this:
class autobus{
public :
autobus();
void affichageTicket();
int calculdesplaces(int typeautobus);
private:
int placeautobus[2][40];
};
The definition of calculdesplaces() doesn't change that much, it just does not shadow the already available array member with a function argument:
int autobus::calculdesplaces(int typeautobus) {
int placenumero;
for (int place = 0; place < 40; place++) {
if ( placeautobus[typeautobus][place] ==0) {
placenumero = place+1;
cout <<"Places : "<< placenumero <<endl;
}
}
return placenumero;
}
And you don't need to "grab into the object" in main(), the array is implicitly passed via the this pointer:
int main() {
int TypeAutobus;
autobus *choixautobus = new autobus();
cout << "1 for smoking bus" << endl;
cout << "2 for non-smoking bus" << endl;
cin >> TypeAutobus;
choixautobus->calculdesplaces(TypeAutobus);
system("PAUSE");
return EXIT_SUCCESS;
}

Answer 3

You haven't mentioned what the error it. But I think this it the issue:
What is the data type of second argument in calculdesplaces function declaration:
int calculdesplaces(int, int);
It is: int
What is the data type of placeautobus[2][40] in calculdesplaces function definition:
int autobus::calculdesplaces(int typeautobus, int *placeautobus[2][40]){ ... }
It is: int*
What is the data type of placeautobus[2][40] in calculdesplaces function call:
choixautobus->calculdesplaces(TypeAutobus, choixautobus->placeautobus[2][40]);
Looking at class autobus { ... }, it is: int
So there is mismatch between the datatype used in function declaration, definition and call. Try solving this.

Answer 4

The code should not be compiled.
The member function declaration of calculdesplaces
int calculdesplaces(int, int);
does not coinside with its definition
int autobus::calculdesplaces(int typeautobus, int *placeautobus[2][40]){
The type of the second parameter differs.
As for the error message then the function should be called as
choixautobus->calculdesplaces( TypeAutobus, choixautobus->placeautobus );
Take into account that the function has a bug. You pass to the function as the first argument either 1 or 2 and use these values as indices of the array while the valid indices are 0 and 1.
Also the function does not need to have the second parameter because it deals with the data member
int placeautobus[2] [40];
So I would define the class and member functions the following way
class autobus{
public :
int placeautobus[2] [40];
autobus();
void affichageTicket();
int calculdesplaces(int);
};
#include <iostream>
#include "autobus.h"
autobus::autobus() : placeautobus {}
{
}
void autobus::affichageTicket()
{
}
int autobus::calculdesplaces( int typeautobus )
{
int placenumero = 0;
for (int place = 0; place < 40; place++)
{
if ( placeautobus[typeautobus - 1][place] == 0 )
{
placenumero = place+1;
cout <<"Places : "<< placenumero <<endl;
break;
}
}
return placenumero;
}
Though I do not understand what you return from the function.:)
Also you could specify the initialization of the array inside the class definition
class autobus{
public :
int placeautobus[2] [40] = {};
//...
In this case the main can look as
int main()
{
int TypeAutobus;
autobus *choixautobus = new autobus();
cout << "1 for smoking bus" << endl;
cout << "2 for non-smoking bus" << endl;
cin >> TypeAutobus;
choixautobus->calculdesplaces( TypeAutobus );
system("PAUSE");
return EXIT_SUCCESS;
}