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Print Spiral with 2d array

FredDilb (5)
I'm currently working on an assignment where I'm supposed to create a spiral using a 2d array of ints. I currently have the programming fully working by normal indexing but the assignment is to use indexing from the pointer. While the math is the same in both assignments I'm getting errors in the pointer version. I came here hoping that someone could help me find where I want wrong in my code.

Normal indexing version that works:
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#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
#include <cstring>
using namespace std;

const int maxCol = 20;
const int maxRow = 20;

void makeSpiral(int a[][maxCol], int rows, int cols)
{
    //int left, counter = 1, right, outter, top, bot;
    int left = 0, counter = 1, right = cols - 1, dir = 0, top = 0, bot = rows - 1;

    while(left<=right && top<=bot)
    {
        if(dir == 0)
        {
            for(int k = left;k<=right;k++)
            {
                //*(pa + rows * top + k) = counter;
                a[top][k] = counter;
                cout << counter << " at: " << top << '\t' << k << "\n";
                counter++;
            }
            top++;
            dir++;
        }
        else if(dir == 1)
        {
            for(int k = top;k<=bot;k++)
            {
                //*(pa + rows * k + right) = counter;
                a[k][right] = counter;
                cout << counter << " at: " << k << '\t' << right << "\n";
                counter++;
            }
            right--;
            dir++;
        }
        else if(dir == 2)
        {
            for(int k = right;k>=left;k--)
            {
                //*(pa + rows * bot + k) = counter;
                a[bot][k] = counter;
                cout << counter << " at: " << bot << '\t' << k << "\n";
                counter++;
            }
            bot--;
            dir++;
        }
        else if(dir == 3)
        {
            for(int k = bot;k>=top;k--)
            {
                //*(pa + rows * k + left) = counter;
                a[k][left] = counter;
                cout << counter << " at: " << k << '\t' << left << "\n";
                counter++;
            }
            left++;
            dir++;
        }
        dir %= 4;
    }
}

void printSpiral(int a[][maxCol], int rows, int cols)
{
    for (int i = 0; i < maxRow; ++i)
    {
        for (int j = 0; j < maxCol; ++j)
        {
            cout << a[i][j] << '\t';
        }
        cout << endl;
    }
    return;
}

void clearArray(int a[][maxCol], int rows, int cols)
{
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < rows; j++)
        {
            a[i][j] = 0;
        }
    }
    return;
}

int main()
{
    int nRows, nCols;
    int a[maxRow][maxCol] = {0};
    int aSize[10][2] =
                    {
                        {1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}, {4, 7}, {7, 4},
                        {4, 8}, {8, 4}, {15, 20}
                    };
    for( int i = 0; i < 9; i++ )
    {
        clearArray( a, maxRow, maxCol );
        makeSpiral( a, aSize[i][0], aSize[i][1] );
        printSpiral( a, aSize[i][0], aSize[i][1] );
    }

    return 0;
}


Pointer version that works for normal arrays, such as, 3x3, 4x4, 5x5, etc. :
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#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
#include <cstring>
using namespace std;

void makeSpiral(int *pa, int rows, int cols)
{
    int left = 0, counter = 1, right = cols - 1, dir = 0, top = 0, bot = rows - 1;

    // base + (row length * rows to skip) + columns to skip
    while(left<=right && top<=bot)
    {
        if(dir == 0)
        {
            for(int k = left;k<=right;k++)
            {
                *(pa + cols * top + k) = counter;
                cout << counter << " at: " << top << '\t' << k << "\n";
                counter++;
            }
            top++;
            dir++;
        }
        else if(dir == 1)
        {
            for(int k = top;k<=bot;k++)
            {
                *(pa + cols * k + right) = counter;
                cout << counter << " at: " << k << '\t' << right << "\n";
                counter++;
            }
            right--;
            dir++;
        }
        else if(dir == 2)
        {
            for(int k = right;k>=left;k--)
            {
                *(pa + cols * bot + k) = counter;
                cout << counter << " at: " << bot << '\t' << k << "\n";
                counter++;
            }
            bot--;
            dir++;
        }
        else if(dir == 3)
        {
            for(int k = bot;k>=top;k--)
            {
                *(pa + cols * k + left) = counter;
                cout << counter << " at: " << k << '\t' << left << "\n";
                counter++;
            }
            left++;
            dir++;
        }
        dir %= 4;
    }
}

// base + (row length * rows to skip) + columns to skip
void printSpiral(ostream &out, int *pa, int rows, int cols)
{
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < cols; j++)
        {
            //out << *(pa + rows * i + j) << '\t' << flush;
            cout << *(pa + cols * i + j) << '\t' << flush;
        }
        //out << endl;
        cout << endl;
    }
    return;
}

void clearArray(int *pa, int rows, int cols)
{
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < rows; j++)
        {
            *(pa + cols * i + j) = 0;
        }
    }
    return;
}

int main()
{
    ofstream outFile;
    int nRows, nCols, i = 1;
    //char outputFile[20];
    //strcpy(outputFile, argv[i]);
    //cout << outputFile << endl;
    //outFile.open(outputFile);

    int a1[1][1] = {0}, a2[2][2] = {0}, a3[3][3] = {0}, a4[4][4] = {0}, a5[5][5] = {0}, a47[4][7] = {0}, a74[7][4] = {0},
        a48[4][8] = {0}, a84[8][4] = {0}, a20[15][20] = {0};
    int aSize[10][2] =
                    {
                        {1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}, {4, 7}, {7, 4},
                        {4, 8}, {8, 4}, {15, 20}
                    };
    int *arrays[] =
                    {
                        &a1[0][0], &a2[0][0], &a3[0][0], &a4[0][0], &a5[0][0],
                        &a47[0][0], &a74[0][0], &a48[0][0], &a84[0][0],
                        &a20[0][0]
                    };

    for( int i = 0; i < 10; i++ )
    {
        //outFile << "Array "<< i+1 << ":\n";
        cout << "rows: " << aSize[i][0] << "\tcols: " << aSize[i][1] << endl;
        clearArray( arrays[i], aSize[i][0], aSize[i][1] );//nRows, nCols );
        makeSpiral( arrays[i], aSize[i][0], aSize[i][1] );//nRows, nCols );
        printSpiral( outFile, arrays[i], aSize[i][0], aSize[i][1] );
        //outFile << "\n\n";
    }

    //outFile.close();
    return 0;
}
Last edited on
SakurasouBusters (732)
I don't know how your program works.
What are the contents of your input file?
FredDilb (5)
There is no input file. It uses argc and argv for the arguments. I'm basically trying to run the arrays set in the bottom program. 1x1, 2x2, 3x3, 4x4, 5x5, 4x7, 7x4, 4x8, 8x4, and 15x20. The arrays works up to the point where it hits the odd dimension ones, like 4x7 then it crashes. The top program with normal indexing works perfectly fine with those odd dimension arrays. The bottom one that indexes using pointers crashes at that point.

The bottom program has a pointer to the base of the declared arrays and the aSize arrays passes in the bounds for the arrays.

The arrays are supposed to look like this in the end for example:
4x4 -
Array 4:
1 2 3 4
12 13 14 5
11 16 15 6
10 9 8 7
Last edited on
SakurasouBusters (732)
Remove all argc and argv stuff, specify the file name directly.
Sorry, we cannot test your code that way.
FredDilb (5)
I edited both so they work without any command line arguments. I do see now that there are random trailing number on some of the problems above. Any help would be appreciated.

Solved: My teacher gave us an example program with the math for the pointer access done. He did the math wrong in the example but gave the right format for indexing with a pointer and I fixed it in the example and it works now. I edited the above programs to demonstrate.
Last edited on
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