Issue with counting ints in an array larger than input

d1g1talarts (55)
Only allowed to use iostream library because thats is what the assignment says. i Agree. Vectors would be the bomb diggity here.
trying to calculate the actual number of numbers in a large allocated array for 100 numbers but the user does not have to enter that many numbers every time. How do i check that input[size]!= a null pointer or something like that.
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void uMatrix::calcSize(int input[]) {
	//new *pointer;
	int temp = 0;
	while (input[size] !=NULL) {
		temp++;
	}
	size = temp;
}
Last edited on
Ganado (6849)
A raw array does not hold its size, the programmer must keep track of it independently to prevent buffer overflows (accessing out-of-bound indices).

If I have an int array with 5 elements, the memory looks something like this:

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int arr[5];
for (int i = 0; i < 5; i++)
    arr[i] = (i+1)*(i+1);

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           [0] [1] [2] [3] [4] 
[..., junk, 1,  4,  9, 16, 25, junk, junk junk, ... ]

There is no guarantee that arr[5] == 0, you would be invoking undefined behavior if you tried to access arr[5].

An std::vector can keep track of its own size and be dynamically resized. You might want to look into that. Otherwise, could you provide a more concrete example of what you're trying to do?
d1g1talarts (55)
uMatrix.cpp
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 #include "uMatrix.h"
//uMatrix::uMatrix() {
//
//}
uMatrix::uMatrix(int someArray[])
{
	//initialize variables 
	//allocate array 
	calcSize(someArray);
	Alloc(someArray);
	fillArray(someArray);
	//for(int i=0;i<)
	//Array = new int *[sizeof(matrixA)];//new array size

	////memory allocated for  elements of each column.


	//for (int i = 0; i < rows; i++)
	//	Array[i] = new int[cols];
}

uMatrix::~uMatrix()
{

	for (int i = 0; i < rows; i++)
		delete[] Array[i];
	delete[] Array;
}
//square=total length of 1d array
void uMatrix::sqrt(int square)
{

		double root = square / 3;
		if (square <= 0)
			rows = 0;
		cols = 0;
		for (int i = 0; i < 100; i++) {
			root = (root + square / root) / 2;
		}
		rows = static_cast <int>(root);
		cols = static_cast<int>(root);
	
	/*double temp;
	double x0 = square * (10 * 10); // x0 = 3 * (10^2)

	for (int i = 1; i < size;i ++) {
		temp = 0.5*(x0 + (square / x0));
	}
	*/

	
}
void uMatrix::setSize(int in)
{
	size = in;
}
void uMatrix::calcSize(int input[]) {
	//new *pointer;
	int temp = 0;
	while (input[size] !=NULL) {
		temp++;
	}
	size = temp;
}
void uMatrix::Alloc(int input[]) {
	//size = sizeof(input);
	sqrt(size);
	Array = new int*[rows];
	for (int i = 0; i < rows; i++) {
		Array[i] = new int[cols];

	}
}	

void uMatrix::fillArray(int input[])
{
	
	for (int i = 0; i < rows; i++) {
		//Array[i] = input[i];
		for (int j = 0; j < cols; j++) {
			Array[i][j]=input[i];
		}
	}
//	print();
	
}
//void uMatrix::allocArray()
//{
//	Array = new int*[rows];
//	for (int i = 0; i < rows; i++) {
//		Array[i] = new int[cols];
//}
//
//void uMatrix::input(std::string input) {
//	std::string fileName;
//	ifstream inFile(fileName);
//	if (!inFile) {
//		cout << "There was an error in opening the file.";
//	}
//	else {
//
//	}
//}

void uMatrix::print()
{
	//for (int i = 0; i < rows; i++) {
	//	
	//	for (int i = 0; i < cols; i++) {
	//		cout << Array[i];
	//	}
	//}
	for (int i = 0; i < rows; i++)
	{
		for (int j = 0; j < cols; j++)
		{
			cout << Array[i][j]<< "  ";
		}
		cout << endl;
	}
}

uMatrix uMatrix::MM(uMatrix B)
{
	uMatrix temp (*this->Array);

		for (int i = 0; i < rows; i++) {
			for (int k = 0; k< B.cols; k++) {
				temp.Array[i][k] = 0;

				for (int j = 0; j < cols; j++)

				{

					temp.Array[i][j] += Array[i][j] * B.Array[j][k];

				}
			}
		}
	
	/*for (int i = 0; i < size; i++) {
		temp[i] += *B.Array[i] * *Array[i];
	}*/
	return temp;
}

uMatrix uMatrix::MMf(uMatrix B)
{
	//idea here is to combine two loops to reduce computation time. 
	uMatrix temp(*B.Array);
	for (int ij  = 0; ij < cols*cols; ij++)
	{
		int i = ij / cols;
		int j = ij % cols;

		temp.Array[i][j] = 0;
		for (int k = 0; k < cols; k++)
			temp.Array[i][j] += Array[i][k] * B.Array[k][j];
	}
	//attempted a single index solution. 
	/*for (int i = 0; i < rows; i++)
	{
		for (int k = 0; k< B.cols; k++) {
			temp.Array[i][k] = 0;

			for (int j = 0; j < cols; j++)

			{

				temp.Array[i*cols+j] += Array[i][j] * B.Array[j][k];

			}
		}
	}*/
	
	return temp;
}

uMatrix uMatrix::MA(uMatrix B)
{

	//added another loop to make the other one faster. thus potato creator is the potato number
	uMatrix temp(*Array);
	for (int PotatoNumber = 0; PotatoNumber < size; ++PotatoNumber) {
		for (int i = 0; i < rows; i++) {
			for (int j = 0; j < cols; j++) {
				temp.Array[i][j] = Array[i][j] + B.Array[i][j];
			}
		}
	}
	return temp;
}

uMatrix uMatrix::MAf(uMatrix B)
{
	uMatrix temp(*Array);
	for (int i = 0; i < rows; i++) {
		for (int j = 0; j < cols; j++) {
			temp.Array[i][j] = Array[i][j] + B.Array[i][j];
		}
	}
	return temp;
}

uMatrix uMatrix::SM(int S)
{
	for (int i = 0; i < rows; i++) {
		for (int j = 0; j < cols; j++) {
			Array[i][j] = Array[i][j] * S;
		}
	}
	return *this;
}

uMatrix uMatrix::SMf(int S)
{
	// i feel like a cant reduce this lower than 2 loops
	for (int i = 0; i < rows; i++) {
		for (int j = 0; j < cols; j++) {
			Array[i][j] = Array[i][j] * S;
		}
	}
	return *this;
}

uMatrix uMatrix::SA(int S)
{
	for (int i = 0; i < rows; i++) {
		for (int j = 0; j < cols; j++) {
			Array[i][j] = Array[i][j] + S;
		}
	}
	return *this;
}

uMatrix uMatrix::SAf(int S)
{
	//i honestly dont know how to make this any faster. 
	for (int i = 0; i < rows; i++) {
		for (int j = 0; j < cols; j++) {
			Array[i][j] = Array[i][j] + S;
		}
	}
	return *this;
}


main.cpp
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#include "uMatrix.h"
int array1[MAX];
int array2[MAX];
int tempScale;

int main(int argc, char **argv)
{
	cout << "hello world\n";
	//string lineInput = " ";
	//while (lineInput.length()>0) {
	//	cin >> lineInput;
	//	//cout << lineInput;
	//}
	////ifstream inFile(*argv);
	//std::string fileName;
	//ifstream inFile;
	//inFile.open(fileName); 
	//if (!inFile) {
	//	cout << "There was an error in opening the file.";
	//}
	//else {

	//	//array1[] = inFile.getline();
	//}
	//
	//You should probably read in two matrices and a scalar value
	int tempSize;

	//bool file = false;
	std::string fileName;
	// diddnt know how else to make a variable limit for the amount of numbers input without a vector.
	cout << "how many numbers will be in your array? ";
	cin >> tempSize;
	if (cin.fail()) {
		cin.clear();
		cin.ignore();
		cout << "There was an error with the number you put in, try again: ";
		cin >> tempSize;
	}
	//	array1(tempSize);
	//cout << "Enter your entire first array: ";

	cout << "fill your array by entering a row of numbers: ";//seperated by white space
	int n;
	for (int i = 0; i < tempSize; i++) {

		/*cin>>n;
		if (cin.fail()) {
			cin.clear();
			cin.ignore();

		}
		else {*/
		cin >> array1[i];

	}



	//	array2[tempSize];
	//string lineInput = " ";
	//while (lineInput.length() > 0)){
	cout << "fill your second array";
	for (int i = 0; i < tempSize; i++) {
		/*cin >> n;
		if (cin.fail()) {
			cin.clear();
			cin.ignore();
		}
		else {*/
		cin>>array2[i];
		//cin >> n;
	}



	cout << "Enter a value to be the scalar: ";
	cin >> tempScale;
	int S = tempScale;

	
	uMatrix A(array1);
	A.setSize(tempSize);
    uMatrix B(array2);
	B.setSize(tempSize);
	//cout << "Enter a value to be the scalar: ";
	//int tempScale;
	//cin >> tempScale;
 //   int S = tempScale;
 //   
    //How about multiplying those two and creating a new uMatrix C?
    
    uMatrix C = A.MM(B);
	C.print();
    //Add C to B?
    
    uMatrix D = B.MA(C);
    
    //Scalar Add to A?
    
    uMatrix E = A.SA(S);
    
    // so on...
	A.~uMatrix();
	B.~uMatrix();
	C.~uMatrix();
	D.~uMatrix();
	E.~uMatrix();
	system("pause");
	return 0;
}

diddnt want to do that. but if it helps you help me by all means look at how poorly i code. Help me please :D!
Last edited on
Ganado (6849)
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int array1[MAX];
int array2[MAX];

When you first declare an array, it has uninitialized values. If you want to set uninitialized values to zero, initialize each array by doing
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int array1[MAX] = {}; // initializes each element to its default value, 0.
int array2[MAX] = {};


Then, when you fill in your array, say, with {1, 2, 3, 4, 5}, the rest of the numbers will be 0.
{1, 2, 3, 4, 5, 0, 0, 0, 0, ...}.

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	int temp = 0;
	while (input[size] != 0) {
		temp++;
	}
	size = temp;

Note that this won't be able to detect when 0 is actual valid data; you are treating 0 as a sentinel value in this manner.

Also, note you're not really supposed to call the destructors manually.
Last edited on
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