Suspicious Pointer Conversion

**stumon** · 04-10-2003

Dude, i dont know what your doing wrong then cause it runs fine on both my computers, here at work and at home. this is my output(top is cut off because my dos does not scroll - win98). I ran a 2x3 * 3x2 matrice and entered all 2's.

Code:

[ 2 * 2 += 68 ]
[ 2 * 2 += 72 ]
[ 2 * 2 += 76 ]
[ 2 * 2 += 80 ]
[ 2 * 2 += 84 ]
[ 2 * 2 += 88 ]
[ 2 * 2 += 92 ]
[ 2 * 2 += 96 ]
[ 2 * 2 += 100 ]
[ 2 * 2 += 104 ]
[ 2 * 2 += 108 ]
[ 2 * 2 += 112 ]
[ 2 * 2 += 116 ]
[ 2 * 2 += 120 ]
[ 2 * 2 += 124 ]
[ 2 * 2 += 128 ]
[ 2 * 2 += 132 ]
[ 2 * 2 += 136 ]
[ 2 * 2 += 140 ]
[ 2 * 2 += 144 ]


[36][36]
[36][36]

Here is a 2x3 * 2x3 matrice and its output, again the top is cut off.

Code:

[ 2 * 2 += 68 ]
[ 2 * 2 += 72 ]
[ 2 * 2 += 76 ]
[ 2 * 2 += 80 ]
[ 2 * 2 += 84 ]
[ 2 * 2 += 88 ]
[ 2 * 2 += 92 ]
[ 2 * 2 += 96 ]
[ 2 * 2 += 100 ]
[ 2 * 2 += 104 ]
[ 2 * 2 += 108 ]
[ 2 * 2 += 112 ]
[ 2 * 2 += 116 ]
[ 2 * 2 += 120 ]
[ 2 * 2 += 124 ]
[ 2 * 2 += 128 ]
[ 2 * 2 += 132 ]
[ 2 * 2 += 136 ]
[ 2 * 2 += 140 ]
[ 2 * 2 += 144 ]


[24][24][24]
[24][24][24]

Something is wrong on your end, lol, not the code.

**mr_spanky202** · 04-10-2003

any idea what could be wrong?im running borland turbo C++ 2.01

**stumon** · 04-10-2003

Not really, try a different compiler, go to www.cnet.com and search there for their compilers they are very basic, but work. Here at work, im using Digital Mars. It has no UI, but works fine.

**Dave_Sinkula** · 04-10-2003

Originally posted by mr_spanky202
Thanks a lot, copied the code into the compiler and gave it a test ran. Still throws up wrong answers once C and R2 are bigger than one
eg

Code:

7 0 9            4    13             1522   1216 
77 2 63   *  64    17       =    13774  10792
24 91 6       29    46              11737   9196

When should be

Code:

289 505 
2263  3933
6094   2135

I see the same results. How about something like this?

Code:

#include <stdlib.h>
#include <stdio.h>

double *multiply(const double *a, int arows, int acols,
                 const double *b, int brows, int bcols,
                 int *crows, int *ccols)
{
    double *c;
    if ( acols != brows )
    {
        return NULL;
    }
    *crows = arows;
    *ccols = bcols;
    c = malloc(*crows * *ccols * sizeof(*c));
    if ( c != NULL )
    {
        int i, j, k;
        for ( i = 0; i < *crows; ++i )
        {
            for ( j = 0; j < *ccols; ++j )
            {
                int ij = *ccols * i + j;
                c[ij] = 0;
                for ( k = 0; k < acols; ++k )
                {
                    int ik = acols * i + k;
                    int kj = bcols * k + j;
                    double product = a[ik] * b[kj];
                    c[ij] += product;
                }
            }
        }
    }
    return c;
}

void display(const double *matrix, int rows, int cols)
{
    int i,j;
    for ( i = 0; i < rows; ++i )
    {
        for ( j = 0; j < cols; ++j )
        {
            printf("%7g ", matrix[i * cols + j]);
        }
        putchar('\n');
    }
    putchar('\n');
}

int main(void)
{
    int i,j;
    double a[] = /* 3x3 */
    {
         7.0,  0.0,  9.0,
        77.0,  2.0, 63.0,
        24.0, 91.0,  6.0,
    };
    double b[] = /* 3x2 */
    {
         4.0, 13.0,
        64.0, 17.0,
        29.0, 46.0,
    };
    double *c = multiply(a,3,3, b,3,2, &i, &j);
    display(a,3,3);
    display(b,3,2);
    if ( c != NULL )
    {
        display(c,i,j);
        free(c);
    }
    return 0;
}

/* my output
      7       0       9
     77       2      63
     24      91       6

      4      13
     64      17
     29      46

    289     505
   2263    3933
   6094    2135
*/

The following links may be of interest.

By the way, for the all-2's 2x3 * 3x2 I get this.

Code:

+-       -+   +-    -+   +-                                    -+   +-      -+
| 2  2  2 |   | 2  2 |   | (2*2)+(2*2)+(2*2)  (2*2)+(2*2)+(2*2) |   | 12  12 |
| 2  2  2 | * | 2  2 | = | (2*2)+(2*2)+(2*2)  (2*2)+(2*2)+(2*2) | = | 12  12 |
+-       -+   | 2  2 |   +-                                    -+   +-      -+
              +-    -+

**stumon** · 04-10-2003

Ops, didn't see the logic error. Guess what, i fixedit with 1 little thing, that is highlighted in red

Code:

#include <stdio.h>

#define MAX_R 4
#define MAX_C 4

typedef int coord[2];

int OrdEnt (int, int*, int*);
void MatCalc (int [][MAX_R], int [][MAX_C], int[][MAX_C], int, int, int, int);

int OrdEnt (int a, int *r, int *c)
{
	do {
		printf("Enter the order of Matrix %d in the format NxN:\n",a);
		
		scanf ("%dx%d",r,c);
		if (*r>4 || *c>4)
		{
			printf("Order too great\n");
		}
		
	} while  (*r>4 || *c>4);
	return (0);
}

void MatCalc (int Matrix_1[][MAX_R], int Matrix_2[][MAX_C], int  Matrix_3[][MAX_C], 
						int r, int c, int r2, int c2)
{
	
	int j,l,h, m = 0, sum = 0;
	for (j=0; j<r; j++){
		for (l=0; l<c; l++){
			for (m=0; m<r2; m++){
				for (h=0; h<c2; h++){
					sum += Matrix_1[j][l] * Matrix_2[m][h];
					printf("[ %d * %d += %d ]", Matrix_1[j][l], Matrix_2[m][h], sum);
					Matrix_3[j][h] += Matrix_1[j][l] * Matrix_2[m][h];	
				};
				printf("\n");
			};
		};
	};
	
	printf("\n\n");
	for (j = 0; j<r; j++){
		for (l=0; l<c2; l++){
			printf("[%d]", (Matrix_3[j][l])/r2) ;
		};
		printf("\n");
	};
}



int main(void)

{
	int R = 0,R2 = 0, C = 0, C2 = 0;
	int Matrix_1 [MAX_R] [MAX_C];
	int Matrix_2 [MAX_R] [MAX_C];
	int Matrix_3 [MAX_R] [MAX_C] = {0};
	int a = 1, b = 2, c = 3, r_i, c_i;
	char in_c;
	
	
	printf("This program will multiply 2 matrices (up to the order of 4x4),"
		" and display the result\n");
	
	
	do{
		OrdEnt(a,&R,&C);
		printf("Is this correct,y/n?:");
		scanf(" %c",&in_c);
	} while(in_c == 'n' || in_c == 'N');
	
	
	do{
		OrdEnt(b,&R2,&C2);
		printf("Is this correct,y/n?:");
		scanf(" %c",&in_c);
	} while(in_c == 'n' || in_c == 'N');
	
	
	
	for(r_i=0; r_i<R; r_i++){
		printf("\nfor row %d of Matrix_1\n",r_i +1);
		for(c_i=0; c_i<C; c_i++){
			printf("\tEnter element value for column %d:",c_i +1);
			scanf("%d",&Matrix_1 [r_i] [c_i]);
		}
				}
	printf("\n\n");
	for (r_i=0; r_i<R; r_i++){
		for (c_i=0; c_i<C; c_i++){
			printf("[%d]", Matrix_1[r_i][c_i]);
			printf("\n");
		}
	}
	
	
	
	for(r_i=0; r_i<R2; r_i++){
		printf("\nfor row %d of Matrix_2\n",r_i +1);
		for(c_i=0; c_i<C2; c_i++){
			printf("\tEnter element value for column %d:",c_i +1);
			scanf("%d",&Matrix_2 [r_i] [c_i]);
		}
				}
	
	printf("\n\n");
	for (r_i=0; r_i<R2; r_i++){
		for (c_i=0; c_i<C2; c_i++){
			printf("[%d]", Matrix_2[r_i][c_i]);
			printf("\n");
		}
	}
	
	
	MatCalc(Matrix_1,Matrix_2,Matrix_3, R, C, R2, C2);
	
	
	
	
	
	return (0);
	
}

**Dave_Sinkula** · 04-11-2003

>Ops, didn't see the logic error. Guess what, i fixedit with 1 little thing
You don't test the code too much, do you?

Code:

This program will multiply 2 matrices (up to the order of 4x4), and display the
result
Enter the order of Matrix 1 in the format NxN:
3x3
Is this correct,y/n?:y
Enter the order of Matrix 2 in the format NxN:
3x2
Is this correct,y/n?:y

for row 1 of Matrix_1
        Enter element value for column 1:7
        Enter element value for column 2:0
        Enter element value for column 3:9

for row 2 of Matrix_1
        Enter element value for column 1:77
        Enter element value for column 2:2
        Enter element value for column 3:63

for row 3 of Matrix_1
        Enter element value for column 1:24
        Enter element value for column 2:91
        Enter element value for column 3:6


[7]
[0]
[9]
[77]
[2]
[63]
[24]
[91]
[6]

for row 1 of Matrix_2
        Enter element value for column 1:4
        Enter element value for column 2:13

for row 2 of Matrix_2
        Enter element value for column 1:64
        Enter element value for column 2:17

for row 3 of Matrix_2
        Enter element value for column 1:29
        Enter element value for column 2:46


[4]
[13]
[64]
[17]
[29]
[46]
[ 7 * 4 += 28 ][ 7 * 13 += 119 ]
[ 7 * 64 += 567 ][ 7 * 17 += 686 ]
[ 7 * 29 += 889 ][ 7 * 46 += 1211 ]
[ 0 * 4 += 1211 ][ 0 * 13 += 1211 ]
[ 0 * 64 += 1211 ][ 0 * 17 += 1211 ]
[ 0 * 29 += 1211 ][ 0 * 46 += 1211 ]
[ 9 * 4 += 1247 ][ 9 * 13 += 1364 ]
[ 9 * 64 += 1940 ][ 9 * 17 += 2093 ]
[ 9 * 29 += 2354 ][ 9 * 46 += 2768 ]
[ 77 * 4 += 3076 ][ 77 * 13 += 4077 ]
[ 77 * 64 += 9005 ][ 77 * 17 += 10314 ]
[ 77 * 29 += 12547 ][ 77 * 46 += 16089 ]
[ 2 * 4 += 16097 ][ 2 * 13 += 16123 ]
[ 2 * 64 += 16251 ][ 2 * 17 += 16285 ]
[ 2 * 29 += 16343 ][ 2 * 46 += 16435 ]
[ 63 * 4 += 16687 ][ 63 * 13 += 17506 ]
[ 63 * 64 += 21538 ][ 63 * 17 += 22609 ]
[ 63 * 29 += 24436 ][ 63 * 46 += 27334 ]
[ 24 * 4 += 27430 ][ 24 * 13 += 27742 ]
[ 24 * 64 += 29278 ][ 24 * 17 += 29686 ]
[ 24 * 29 += 30382 ][ 24 * 46 += 31486 ]
[ 91 * 4 += 31850 ][ 91 * 13 += 33033 ]
[ 91 * 64 += 38857 ][ 91 * 17 += 40404 ]
[ 91 * 29 += 43043 ][ 91 * 46 += 47229 ]
[ 6 * 4 += 47253 ][ 6 * 13 += 47331 ]
[ 6 * 64 += 47715 ][ 6 * 17 += 47817 ]
[ 6 * 29 += 47991 ][ 6 * 46 += 48267 ]


[517][405]
[4591][3597]
[3912][3065]

It seems we'd like to get this.

Code:

[289][505]
[2263][3933]
[6094][2135]

You might want to take a look at these elements.

Code:

void MatCalc (int Matrix_1[][MAX_R], int Matrix_2[][MAX_C], int  Matrix_3[][MAX_C],
              int r, int c, int r2, int c2)
{

    int j,l,h, m = 0, sum = 0;
    for ( j=0; j<r; j++ )
    {
        for ( l=0; l<c; l++ )
        {
            for ( m=0; m<r2; m++ )
            {
                for ( h=0; h<c2; h++ )
                {
                    sum += Matrix_1[j][l] * Matrix_2[m][h];
                    printf("[ %d * %d += %d ]", Matrix_1[j][l], Matrix_2[m][h], sum);
                    Matrix_3[j][h] += Matrix_1[j][l] * Matrix_2[m][h];
                };
                printf("\n");
            };
        };
    };

    printf("\n\n");
    for ( j = 0; j<r; j++ )
    {
        for ( l=0; l<c2; l++ )
        {
            printf("[%d]", (Matrix_3[j][l])/r2) ;
        };
        printf("\n");
    };
}

Maybe try this.

Code:

void MatCalc (int Matrix_1[][MAX_C], int Matrix_2[][MAX_C], int  Matrix_3[][MAX_C],
              int r, int c, int r2, int c2)
{

    int j,l,m;
    for ( j=0; j<r; j++ )
    {
        for ( l=0; l<c2; l++ )
        {
            for ( m=0; m<r2; m++ )
            {
                Matrix_3[j][l] += Matrix_1[j][m] * Matrix_2[m][l];
                printf("[ %d * %d += %d ]\n", Matrix_1[j][m], Matrix_2[m][l],
                       Matrix_3[j][l]);
            }
        }
    }

    printf("\n\n");
    for ( j = 0; j<r; j++ )
    {
        for ( l=0; l<c2; l++ )
        {
            printf("[%d]", (Matrix_3[j][l])) ;
        };
        printf("\n");
    }
}

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