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    Need help with matrix in C


    hi there
    im newbie in C programming, started a few months ago, and i got an assignment wich involves matrix
    I have to rearrange columns of a matrix in ascending order, in dependence of column characteristics, now a column characteristic is considered
    module sum of odd negative elements
    for example:
    -7 2 1
    -3 -5 2
    1 4 -3
    the characteristics are 10 5 and 3
    My code so far

    Code:
    #include <stdio.h>
    #include <conio.h>
    #define M 5 /* Max matrix dimension*/
    void main ()
        {   int nl,nc;   /* nl  lines, nc columns*/
        int tab1[M][M], i, j, s=0, tab2[M][M], tab3[M],temp,g,temp2,tab4[M],k;
    
        printf("Enter matrix dimension: \n");
        printf ("line number: "); scanf("%d",&nl);
        printf ("column number: "); scanf ("%d",&nc);
        if (nl >M || nc >M)
          {  printf("Error: dimensions >5 \n"); return;}
    
        printf("Enter matrix elements\n");
        for (i=0;i<nl;i++)
         for (j=0;j<nc;j++)
            {printf(" elem[%d][%d]:",i,j);
              scanf ("%d", &tab1[i][j]);
            }
    
              printf("Your matrix [%d][%d]\n",nl,nc);
                for (i=0;i<nl;i++)
                {
                for (j=0;j<nc;j++)
                    printf(" %3d ", tab1[i][j]);
                    printf("\n");
                }
    
    for (i=0;i<nl;i++)
        for (j=0;j<nc;j++)
            if(tab1[i][j]<0 && tab1[i][j]%2!=0) // searching negative odd elements
             tab2[i][j]=fabs(tab1[i][j]);
            else
                tab2[i][j]=0;
    
    
     for (j=0;j<nc;j++){
          s=0;
          for (i=0;i<nl;i++)
           s+=tab2[i][j];
            tab3[j]=s;}
        
    printf("tab3\n");
    for(j=0; j<nc; j++)
        printf(" %3d ",tab3[j]);
        printf("\n");
    
    do
     {g=0;
    
         for (j=0;j<nc;j++)
    
            if (tab3[j]>tab3[j+1])
                {temp2=tab3[j];
                tab3[j]=tab3[j+1];
                tab3[j+1]=temp2;
    for (j=0;j<nc;j++)
          {for (i=0;i<nl;i++)
        
                    temp=tab1[i][j];       
                    tab1[i][j]=tab1[i][j+1];
                    tab1[i][j+1]=temp;
    
                    g=1;}}
    
      }while (g==1);
    
    
     printf("Final matrix\n");
                for (i=0;i<nl;i++)
                {
                for (j=0;j<nc;j++)
                    printf(" %3d ", tab1[i][j]);
                    printf("\n");
    
        }
    unfortunately it doesnt do the job
  2. #2
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    Well you could edit your post to use [code][/code] tags instead of inventing your own.

    Few can be bothered to even look through unformatted code. Those that do will only do so if they have time at the end, and only if the other thing on offer is even worse (like root canal denture work).
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper
  4. #3
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    any ideas? it will realy help
  6. #4
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    Well I was hoping for something better, but still - early days I suppose.
    Code:
    #include <stdio.h>
    #include <math.h> //!! for fabs
    //#include <conio.h>
    #define M 5                     /* Max matrix dimension */
    
    //!! Define some useful functions, so your main doesn't grow
    //!! to some unmanageable size.
    void inputMatrix ( int rows, int cols, int (*mat)[M] ) {
      int i, j;
      printf("Enter matrix elements\n");
      for (i = 0; i < rows; i++)
        for (j = 0; j < cols; j++) {
          printf(" elem[%d][%d]:", i, j);
          scanf("%d", &mat[i][j]);
        }
    }
    void printMatrix ( int rows, int cols, int (*mat)[M] ) {
      int i, j;
      printf("Your matrix [%d][%d]\n", rows, cols);
      for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++)
          printf(" %3d ", mat[i][j]);
        printf("\n");
      }
    }
    
    int main()  //!! yes, really, it does return int
    {
      //!! picking better (more descriptive) variable names
      //!! would be a good idea.
      int nl, nc;                   /* nl  lines, nc columns */
      int tab1[M][M], i, j, s = 0, tab2[M][M], tab3[M], temp, g, temp2, tab4[M], k;
    
      printf("Enter matrix dimension: \n");
      printf("line number: ");
      scanf("%d", &nl);
      printf("column number: ");
      scanf("%d", &nc);
      if (nl > M || nc > M) {
        printf("Error: dimensions >5 \n");
        return;
      }
    
      //!! use the utility functions
      inputMatrix( nl, nc, tab1 );
      printMatrix( nl, nc, tab1 );
    
      //!! does what?
      for (i = 0; i < nl; i++)
        for (j = 0; j < nc; j++)
          if (tab1[i][j] < 0 && tab1[i][j] % 2 != 0)  // searching negative odd elements
            tab2[i][j] = fabs(tab1[i][j]);
          else
            tab2[i][j] = 0;
    
      //!! does what?
      for (j = 0; j < nc; j++) {
        s = 0;
        for (i = 0; i < nl; i++)
          s += tab2[i][j];
        tab3[j] = s;
      }
    
      printf("tab3\n");
      for (j = 0; j < nc; j++)
        printf(" %3d ", tab3[j]);
      printf("\n");
    
      do {
        g = 0;
        for (j = 0; j < nc; j++)
          if (tab3[j] > tab3[j + 1]) {
            temp2 = tab3[j];
            tab3[j] = tab3[j + 1];
            tab3[j + 1] = temp2;
            for (j = 0; j < nc; j++) {
              for (i = 0; i < nl; i++)
                temp = tab1[i][j];
    
              //!! Here is your possible bug
              //!! whatever your indentation may say, the
              //!! next two lines are NOT part of the inner
              //!! for loop.  So the value of i used here
              //!! is off the end of the matrix
              tab1[i][j] = tab1[i][j + 1];
              tab1[i][j + 1] = temp;
    
              g = 1;
            }
          }
      } while (g == 1);
    
      printMatrix( nl, nc, tab1 );
      
      return 0; //!! added
    }
    Pay attention to all the //!! comments.

    If there is one lesson you should learn from this, it's that you should treat all optional use of { } as being compulsory.

    Look at your big for / if / for / for nested construct with only TWO pairs of braces.

    Now I want you to go through all your code, and put in { } in all the places where you're treating them as optional.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper
  8. #5
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    ok, but this may take a while
  10. #6
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    I did it! works like a charm
    here is my new code
    Code:
    #include <stdio.h>
    #include <math.h> 
    #define M 5                     /* Max matrix dimension */
    
    
    void inputMatrix ( int rows, int cols, int (*mat)[M] ) {
      int i, j;
      printf("Enter matrix elements\n");
      for (i = 0; i < rows; i++)
        for (j = 0; j < cols; j++) {
          printf(" elem[%d][%d]:", i, j);
          scanf("%d", &mat[i][j]);
        }
    }
    void printMatrix ( int rows, int cols, int (*mat)[M] ) {
      int i, j;
      printf("Your matrix [%d][%d]\n", rows, cols);
      for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++)
          printf(" %3d ", mat[i][j]);
        printf("\n");
      }
    }
    
    int main() 
    {
    
      int nl, nc;                   /* nl  lines, nc columns */
      int tab1[M][M], i, j, s = 0, tab2[M][M], tab3[M], temp, g, temp2;
    
      printf("Enter matrix dimension: \n");
      printf("line number: ");
      scanf("%d", &nl);
      printf("column number: ");
      scanf("%d", &nc);
      if (nl > M || nc > M) {
        printf("Error: dimensions >5 \n");
        return;
      }
    
    
      inputMatrix( nl, nc, tab1 );
      printMatrix( nl, nc, tab1 );
    
    // searching negative odd elements
      for (i = 0; i < nl; i++)     
        for (j = 0; j < nc; j++)
          if (tab1[i][j] < 0 && tab1[i][j] % 2 != 0)
            tab2[i][j] = fabs(tab1[i][j]);
          else
            tab2[i][j] = 0;
    
      //!! Copying the sum of negative odd elements
      for (j = 0; j < nc; j++)
      {
        s = 0;
        for (i = 0; i < nl; i++)
          s += tab2[i][j];
        tab3[j] = s;
      }
    
      printf("tab3\n");
      for (j = 0; j < nc; j++)
        printf(" %3d ", tab3[j]);
      printf("\n");
    
      do {
        g = 0;
        for (j = 0; j < nc; j++)
          if (tab3[j] > tab3[j + 1])
          {
            temp2 = tab3[j];
            tab3[j] = tab3[j + 1];
            tab3[j + 1] = temp2;
    
                for (i = 0; i < nl; i++)
                  {temp = tab1[i][j];
                  tab1[i][j] = tab1[i][j + 1];
                  tab1[i][j + 1] = temp;
    
              g = 1;
    
          }}
      } while (g == 1);
    
    
      printMatrix( nl, nc, tab1 );
    
    
      return 0;
    }
    thanks a lot, you realy helped me
    btw int (*mat)[M] why did you put this pointer?

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