access pointer to array in struct

[Alpine1989]

Hello,

first, thanks to the website and the community, u helped me a lot :-)

my problem: I want to use 1 array for some issues: save memory.
I have to run -1 again to use the main function.. why? and it changes the value of first value of array.. how can I fix this?

I know how to fix the value problem with a patch, but I want to fix/understand the main/basic problem. And i don't want to type the -1 twice.

Thank you already :-)

  
#include<iostream>

using namespace std;




struct ArrData {		//to return pointer AND size of array (2 returns of function)
	double* Ptr;
	int Max;
};

ArrData ArrFunc();



ArrData  ArrFunc() {

	
	
	int i = 0;
	double fill = 0;			
	static double arr[30];
	static ArrData AD;			//sum of returns in struct, size and pointer of array
	AD.Ptr = arr;

	while (fill != -1) {		// fill array until -1
		cin >> fill;
		arr[i] = fill;
		i++;
	}

	for (int j = 0; j < i; j++) {									//searching for bug	- until here everything working well
		cout << (AD.Ptr + j) << " -> " << *(AD.Ptr + j) << endl;
	}

	
	cout << "Test AD.Ptr result: " << *AD.Ptr << endl;		//show me fine answer first, after the buggy needed -1 again it is activated again and write -1 in array, so first fault is here in the function i think
	AD.Max = (i-1); //-1 to ignore the -1 in arry
	return AD;
}

int main() {
	
	int i, MAX = ArrFunc().Max;
	double * p = ArrFunc().Ptr;


	for (i = 0; i < MAX; i++) {								//here i need to insert -1 again... why??? and get bad/wrong results too
		cout << (p + i) << " -> " << *(p + i) << endl;		// print adress of pointer and value

	}
	for (i = 0; i < MAX; i++) {									//working fine too
		*(p + i) = i-1;
		cout << "Neuer Wert: " <<  (p + i) << " -> " << *(p + i) << endl;

	}


	
	return 0;
}

[jonnin]

double fill = 0;

while (fill != -1) <-------- comparison of a double to an exact value can be buggy. You might get fill really being -0.9999999999999999999988 instead, for example.

consider changing the code to do this some other way, whether that is to read in a string, check the string value, and convert it to a double to load it, or whatever other approach seems useful.

This is probably not your main issue, but something else to consider and be aware of.

[Alpine1989]

Thanks for your answer!
I tried some other methods and changed all in integer, for example:

do {		// fill array until -1
		cin >> fill;
		arr[i] = fill;
		i++;
	} while (i < 10);

i got a feeling my fault is not here :(

#include<iostream>

using namespace std;




struct ArrData {		//to return pointer AND size of array (2 returns of function)
	int* Ptr;
	int Max;
};

ArrData ArrFunc();



ArrData  ArrFunc() {

	
	int fill = 0;
	int i = 0;
	static int arr[30] = {2, 3, 4, 5, 6, 7, 8, 9, 10};
	static ArrData AD;			//sum of returns in struct, size and pointer of array
	AD.Ptr = arr;

	
	cout << "Test AD.Ptr result: " << *AD.Ptr << endl;		// this thing got printed twice.., somehting is repeating itself here..
	AD.Max = (i-1); //-1 to ignore the -1 in arry
	return AD;
}

int main() {
	
	int i, MAX = ArrFunc().Max;
	int * p = ArrFunc().Ptr;


	for (i = 0; i < MAX; i++) {								//here i need to insert -1 again... why??? and get bad/wrong results too
		cout << (p + i) << " -> " << *(p + i) << endl;		// print adress of pointer and value

	}
	for (i = 0; i < MAX; i++) {									//working fine too
		*(p + i) = i-1;
		cout << "new value: " <<  (p + i) << " -> " << *(p + i) << endl;

	}


	
	return 0;
}

i found the problem, can u help me to solve it?

in Main:
int i, MAX = ArrFunc().Max;
	int * p = ArrFunc().Ptr;

to get Max and pointer the function works twice, how can i get the values without repeating?

[Alpine1989]

SOLVED..
i worked on this 3 days... lol :-)

here is my code

#include<iostream>

using namespace std;


struct ArrData {		
	int* Ptr;
	int Max;
};

ArrData ArrFunc();

ArrData  ArrFunc() {

	
	int fill = 0;
	int i = 0;
	static int arr[30];
	static ArrData AD;			//sum of returns in struct, size and pointer of array
	AD.Ptr = arr;

	
	do {		// fill array until -1
		cin >> fill;
		arr[i] = fill;
		i++;
	} while (fill != -1);

	for (int j = 0; j < i-1; j++) {							
		cout << (AD.Ptr + j) << " -> " << *(AD.Ptr + j) << endl;
	}
	
	AD.Max = (i-1); //-1 to ignore the -1 in arry
	return AD;
}

int main() {
	
	ArrData x = ArrFunc();   // solved here
	int i;

	for (i = 0; i < x.Max; i++) {								
		cout << (x.Ptr + i) << " -> " << *(x.Ptr + i) << endl;		// print adress of pointer and value

	}
	for (i = 0; i < x.Max; i++) {	
		cout << "new value: " <<  (x.Ptr + i) << " -> " << *(x.Ptr + i)+3 << endl;  //change values

	}


	
	return 0;
}