qsort problem.

This is a discussion on qsort problem. within the C++ Programming forums, part of the General Programming Boards category; Hello, I have a problem with qsort. I let my program generate 50x40 arrays and after i used qsort. The ...

  1. #1
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    qsort problem.

    Hello,

    I have a problem with qsort. I let my program generate 50x40 arrays and after i used qsort. The result is not 50x40 anymore. It become a

    here is my code
    Code:
    #include <iostream>
    #include <ctime> 
    #include <cstdlib> 
    #include <iomanip>
    using namespace std;
    int compare (const void * a, const void * b)
    {
      return ( *(int*)a - *(int*)b );
    }
    
     
    int main()
    {
        const int row=50;
        const int column=40;
        int table[row][column];
        int rnum;
        int t[row];
     
        srand(time(0)); 
        rnum = (rand() % 100) + 1; 
    
        for(int r=0; r<row; r++)//row
        { 
            for(int c=0; c<column; c++)
                table [r][c] = (rand()%100) + 1;
        }
     
        for(int r=0; r<row; r++)//row
        { 
            for(int c=0; c<column; c++) //column
     
            {
                cout << setw(3) << table[r][c] << ' '; //display table
     
            }
            cout << endl;
        } 
          qsort(table, 50 * 40, sizeof(int), compare);
    
     
        cout << "your new sorted table is: \n";
    
        for(int n=0; n<row; n++)//row
        { 
            for(int m=0; m<column; m++) //column
     
            {
                cout << setw(3) << table[n][m] << ' '; //display table
     
            }
        }
    
    
    
        
     
        
     
            system("pause");
            return 0;
     
    }

  2. #2
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by witt
    I have a problem with qsort.
    Is there any reason why you don't use std::sort?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    well I dont even know how to use it or even what it meant sorry

  4. #4
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    std::qsort(table, 5 * 4, sizeof(int), compare); like this?

  5. #5
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    well it still not working
    Last edited by witt; 11-15-2011 at 08:55 PM.

  6. #6
    Algorithm Dissector iMalc's Avatar
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    Since this is C++, forget about qsort. In C++ we use std::sort.
    However, regardless of what you use, you have to understand and convey to us, what it means to be sorting a 2D array.

    And no sorting cannot change the dimensions of an array. Your assumption that this is happening is wrong.
    My homepage
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  7. #7
    Kiss the monkey. CodeMonkey's Avatar
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    You can sort each row, and then sort the columns... or you can define some ordering (zig-zag) and sort it that way. What are you trying to do?
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

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