我可以通过同时索引c中的两个矩阵将矩阵的值传递给另一个矩阵吗？

Question

I am writing a piece of code that uses a struct and 5 predefined functions, I am having problems passing the values of the input 2d array at a chosen index to a new 2d array.

I have included my functions and the code for function I am having difficulties with.

struct matrix
{
char name;
int mValues[10][10];
int ncols;
int nrows;
};

void matrixInput(struct matrix *matA);
void matrixDisplay(struct matrix matA);
void matrixTrace(struct matrix matA, int *trace);
void matrixDeterminant(struct matrix m1, struct matrix *m2, int * determinant);


///function body 
void matrixDeterminant(struct matrix m1, struct matrix *m2, int * determinant)
{
int i, j, k, l;
FILE* fin;
fin = fopen("marks.txt", "r");
if(((m1.nrows)>2))
{
    printf("\n\nFinding the deterinamt now.\n");
    if(fin!=NULL)
    {
        do
        {
             printf("Please assign a letter to name your matrix A - Z : ");
             scanf(" %c", &((*m2).name));
        }
             while((((*m2).name)<'A') || ((*m2).name)>'Z');
        do
        {
             printf("\n\nEnter the row where you want to start the 2x2 matrix.\nNumber needs to be between 1 and %d : ", ((m1).nrows-1));
             scanf("%d", &k);
        }
             while((k) >= ((m1).nrows));
        do 
        {
             printf("\n\nEnter the column where you want to start you 2x2 mtrix.\nNumber needs to be between 1 and %d : ", ((m1).ncols-1));
             scanf("%d", &l);
        }
             while((l) >= ((m1).ncols));
    }

    for(i=0; i<2; i++,k++)
        {
             printf("Row %d:\t", i+1);

             for(j=0; j<2; j++,l++)
                 {
                    ((*m2).mValues[i][j]) = ((m1).mValues[k-1][l-1]);
                    printf("%d\t",((*m2).mValues[i][j])); 
                 }
                 printf("\n");
        }

}

/// Input/Output
Please assign a letter to name your matrix A - Z : H

Please enter the number of rows in matrix H > 1 < 10 :8

Please enter the number of cols in matrix H > 1 < 10 :8

Matrix H has 8 rows and 8 columns and contains:

Row 1:  55  7   40  30  32  45  43  77
Row 2:  72  1   20  65  85  40  46  22  
Row 3:  45  77  88  32  30  55  59  99  
Row 4:  72  37  33  18  44  73  44  12  
Row 5:  88  2   11  55  7   40  30  32  
Row 6:  24  73  13  99  99  22  45  77  
Row 7:  88  32  22  11  98  34  38  37  
Row 8:  33  18  44  73  22  45  77  88 

Trace of matrix H = 317 

Finding the deterinamt now.
Please assign a letter to name your matrix A - Z : F

Enter the row where you want to start the 2x2 matrix.
Number needs to be between 1 and 7 : 3

Enter the column where you want to start you 2x2 mtrix.
Number needs to be between 1 and 7 : 3
Row 1:  88  32  
Row 2:  44  73   // This has shifted 2 columns. 

Process returned 0 (0x0)   execution time : 14.807 s
Press ENTER to continue.

The First function lets the user name and define the dimensions of the matrix which is then populated from a .txt file containing 10x10 integers.

The second function displays the matrix and the third calculates the trace.

The fourth function asks the user to choose a 2x2 matrix, which is a subset of the original matrix. The 2x2 matrix contents must be stored in a new struct matrix, along with its name and size.

What I "think" I have done, is to ask the user where to start the sub-matrix and stored the values at k and l, I then use these values as an index.

Where I believe my problem occurs is in passing these vales to the new matrix, in the nested for loops I have incremented i and j to index the new matrix and l and k to index the matrix I am passing values from.

NOTE: I have never seen 2 values being incremented in a for loop before so I expect it is not doing what I "think" it is doing as row 2 of the sub matrix has shifted 2 columns.

Any help would be appreciated.

Answer 1

Your l that is incremented in the innermost loop is the culprit

for(j=0; j<2; j++,l++)

you need to reinitialize it

for(i=0; i<2; i++,k++)
        {
             printf("Row %d:\t", i+1);

             for(j=0; j<2; j++,l++)
                 {
                    (m2->mValues[i][j]) = ((m1).mValues[k-1][l-1]);
                    printf("%d\t",(m2->mValues[i][j])); 
                 }
                 printf("\n");
                 l=l-2;
        }

Because in the first row l is incremented twice, in the second row it's incremented twice again.

I'd advise you to avoid one letter variables and especially "l" as @JohnColeman said since they are a nightmare at debugging.

Answer 2

Your index l should be reset to the initial value when you exit the second loop ( j loop).

In your case, this is what your indexes look like during execution:

    loop i => i=0, k=3, j=0, l=3  
    loop j => i=0, k=3, j=0, l=3  
    loop j => i=0, k=3, j=1, l=4
    exit loop j => i=0, k=3, j=2, l=5  
    loop i => i=1, k=4, j=2, l=5 
    so on...

So your indexes are corrupted when you exit the second loop !