Array Value

[cplusplusquestion@gmail.com]

I have code in main function:

int main(){
int a[20];
int b[20][20];

for(int i=0; i<20; i++)
a[i]=0;
.......
AClass a(a, b, c);
....
}

For AClass:

class AClass{
private:
int* a1;
int* b1[20];

.....
public:
AClass(int x[], int y[][20], int z);
}

AClass::AClass( int x[], int y[][20], int z): a1(x), c1(z){
for(int i=0; i<MAX; ++i)
edge[i]=e[i];

[cplusplusquestion@gmail.com]

Re: Array Value

Sorry I didn't finish the edited yet:

I have code in main function:

int main(){
int a[20];
int b[20][20];

for(int i=0; i<20; i++)
a[i]=0;
.......
AClass a(a, b, c);
....

}

For AClass:

class AClass{
private:
int* a1;
int* b1[20];
int c1;
.....
public:
AClass(int x[], int y[][20], int z);
.....
}

AClass::AClass( int x[], int y[][20], int z): a1(x), c1(z){

// here a1's value is right //

for(int i=0; i<20; ++i)
b1[i]=y[i];

// a1's value changed to some strange value like
a[0]=-7890987 //

.....
}


When I create an object using constructor AClass, the "a1" value is
assigned wrong, can anyone tell me what's wrong with it?

[joseph cook]

Re: Array Value

On Oct 7, 11:12 pm, cplusplusquest. ..@gmail.com wrote:

Sorry I didn't finish the edited yet:
>
I have code in main function:
>
int main(){
  int a[20];
  int b[20][20];
>
  for(int i=0; i<20; i++)
      a[i]=0;
  .......
  AClass a(a, b, c);

This compiled?? What compiler? You are declaring two variable 'a' in
the same scope. One is an array, and the other is of type "AClass"
Joe C

[cplusplusquestion@gmail.com]

Re: Array Value

On Oct 8, 1:36 pm, joseph cook <joec...@gmail. comwrote:

On Oct 7, 11:12 pm, cplusplusquest. ..@gmail.com wrote:
>

Sorry I didn't finish the edited yet:

>

I have code in main function:

>

int main(){
int a[20];
int b[20][20];

>

for(int i=0; i<20; i++)
a[i]=0;
.......
AClass a(a, b, c);

>
This compiled?? What compiler? You are declaring two variable 'a' in
the same scope. One is an array, and the other is of type "AClass"
Joe C

Sorry again. You are right. The declaration should be AClass
aclass(a, b, c).

[cplusplusquestion@gmail.com]

Re: Array Value

I can only think about the problem may come from array size. However,
the size here only 20, not very big. If I re-write the code as:

for(int i=0; i<19; ++i)
b1[i]=y[i];

It seems no problem. Is there any explanation?

[cplusplusquestion@gmail.com]

Re: Array Value

I can only think about the problem may come from array size. However,
the size here only 20, not very big. If I re-write the code as:

for(int i=0; i<19; ++i)
b1[i]=y[i];

It seems no problem. Is there any explanation?

[Salt_Peter]

Re: Array Value

On Oct 7, 11:44 pm, cplusplusquest. ..@gmail.com wrote:

On Oct 8, 1:36 pm, joseph cook <joec...@gmail. comwrote:
>
>
>

On Oct 7, 11:12 pm, cplusplusquest. ..@gmail.com wrote:

>

Sorry I didn't finish the edited yet:

>

I have code in main function:

>

int main(){
int a[20];
int b[20][20];

>

for(int i=0; i<20; i++)
a[i]=0;
.......
AClass a(a, b, c);

>

This compiled?? What compiler? You are declaring two variable 'a' in
the same scope. One is an array, and the other is of type "AClass"
Joe C

>
Sorry again. You are right. The declaration should be AClass
aclass(a, b, c).

ok, to get you started...
this is a class:

class A { };

this is not:

class A { }

This doesn't compile:

class A
{
public:
A(int z) : n(z) { }
};

int main()
{
A a;
}

but this should:

class A
{
int n;
public:
A(int z) : n(z) { }
};

int main()
{
A a(99);
}

Magic numbers is usually bad news, templates are SO simple:

template < typename T, const std::size_t Size >
class A
{
T array[Size];
public:
A()
{
for( std::size_t i = 0; i < Size; ++i )
array[i] = i;
}
};

int main()
{
A< int, 20 a;
}

See any pointers? No, not directly, why?
Pointers nearly always mean MORE work, less maintainable code, and few
guarentees.
You can pass an array by reference, but even that is a lost exercise.
A solution using std::vector< int would most likely be vastly
superior.

[cplusplusquestion@gmail.com]

Re: Array Value

On Oct 8, 2:45 pm, Salt_Peter <pj_h...@yahoo. comwrote:

On Oct 7, 11:44 pm, cplusplusquest. ..@gmail.com wrote:
>
>
>

On Oct 8, 1:36 pm, joseph cook <joec...@gmail. comwrote:

>

On Oct 7, 11:12 pm, cplusplusquest. ..@gmail.com wrote:

>

Sorry I didn't finish the edited yet:

>

I have code in main function:

>

int main(){
int a[20];
int b[20][20];

>

for(int i=0; i<20; i++)
a[i]=0;
.......
AClass a(a, b, c);

>

This compiled?? What compiler? You are declaring two variable 'a' in
the same scope. One is an array, and the other is of type "AClass"
Joe C

>

Sorry again. You are right. The declaration should be AClass
aclass(a, b, c).

>
ok, to get you started...
this is a class:
>
class A { };
>
this is not:
>
class A { }
>
This doesn't compile:
>
class A
{
public:
A(int z) : n(z) { }
>
};
>
int main()
{
A a;
>
}
>
but this should:
>
class A
{
int n;
public:
A(int z) : n(z) { }
>
};
>
int main()
{
A a(99);
>
}
>
Magic numbers is usually bad news, templates are SO simple:
>
template < typename T, const std::size_t Size >
class A
{
T array[Size];
public:
A()
{
for( std::size_t i = 0; i < Size; ++i )
array[i] = i;
}
>
};
>
int main()
{
A< int, 20 a;
>
}
>
See any pointers? No, not directly, why?
Pointers nearly always mean MORE work, less maintainable code, and few
guarentees.
You can pass an array by reference, but even that is a lost exercise.
A solution using std::vector< int would most likely be vastly
superior.

Thank you for your explanation, I still can't understand why my code
does not work well.

[cplusplusquestion@gmail.com]

Re: Array Value

It seems that I find the problem. I delete old object files and re-
compile it, then the problem is gone. Is this the right answer? If it
is, why?