Problems in generating random matrices in C - c

Question

I wrote a serial program to generate 2 random matrices, multiply them and display the result. I wrote functions for each of the tasks, i.e. generating random matrix, multiplying the matrices and displaying the results. I cannot figure out why both the generated matrices are the same.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int **matrix_generator(int row,int col);
int **multiply_matrices(int **matrix_A,int **matrix_B,int rowsA, int colsA,int rowsB,int colsB);
void display_result(int **matrix,int cols,int rows);
void display_matrix(int **matrixA,int cols,int rows);
void main()
{
int **matrix_A,**matrix_B,**matrix_result,i,j,k,tid,rowsA,colsA,rowsB,colsB;
printf("Enter the dimensions of Matrix A:\n");
scanf("%d%d",&rowsA,&colsA);
printf("Enter the dimensions of Matrix B:\n");
scanf("%d%d",&rowsB,&colsB);
if(colsA==rowsB)
{
matrix_A = matrix_generator(rowsA,colsA);
matrix_B = matrix_generator(rowsB,colsB);
matrix_result = multiply_matrices(matrix_A,matrix_B,rowsA,colsA,rowsB,colsB);
printf("Matrix A:\n");
display_matrix(matrix_A,rowsA,colsA);
printf("\n\n");
printf("Matrix B:\n");
display_matrix(matrix_B,rowsB,colsB);
printf("\n\n");
display_matrix(matrix_result,rowsB,colsA);
}
else
{
printf("Check the dimensions of the matrices!\n");
exit(-1);
}
}
int **matrix_generator(int row, int col)
{
int i, j, **intMatrix;
intMatrix = (int **)malloc(sizeof(int *) * row);
srand(time(0));
for (i = 0; i < row; i++)
{
intMatrix[i] = (int *)malloc(sizeof(int *) * col);
for (j = 0;j<col;j++)
{
intMatrix[i][j]=rand()%10;
}
}
return intMatrix;
}
int **multiply_matrices(int **matrix_A,int **matrix_B,int rowsA, int colsA,int rowsB,int colsB)
{
int i, j, k, **resMatrix;
resMatrix = (int **)malloc(sizeof(int *) * rowsB);
for (i = 0; i < rowsA; i++)
{
resMatrix[i] = (int *)malloc(sizeof(int *) * colsA);
for (j = 0;j<colsB;j++)
{
for (k = 0; k < colsA; k++)
resMatrix[i][j] = resMatrix[i][j] + matrix_A[i][k] * matrix_B[k][j];
}
}
return resMatrix;
}
void display_matrix(int **matrix, int rows,int cols)
{
int i,j;
for (i = 0; i < rows; i = i + 1)
{
for (j = 0; j < cols; j = j + 1)
printf("%d ",matrix[i][j]);
printf("\n");
}
}
OUTPUT:
Enter the dimensions of Matrix A:
4
4
Enter the dimensions of Matrix B:
4
4
Matrix A:
8 7 8 4
9 8 3 9
1 2 0 4
6 0 2 3
Matrix B:
8 7 8 4
9 8 3 9
1 2 0 4
6 0 2 3
159 128 93 139
201 133 114 147
50 23 22 34
68 46 54 41
Can someone please help me understand where I'm going wrong? I have a pretty good idea that it's the matrix_generator() function but cannot seem to figure out what's wrong. Also, It's only multiplying square matrices, if the dimensions are different, like 4X5 and 5X4, I get a segmentation fault.

Answer 1

There are a few issues in your code:
1) You allocate memory incorrectly:
in multiply_matrices should be
resMatrix[i] = (int *)malloc(sizeof(int) * colsB);
and in matrix_generator
intMatrix[i] = (int *)malloc(sizeof(int) * col);
2) In main if you want to print matrix_result call
display_matrix(matrix_result,rowsA,colsB);
Dimensions of [rowsA,colsA] x [rowsB,colsB] is rowsA x colsB
3) malloc returns pointer to uninitialized memory, so you should set resMatrix elements to zero before summing
Content of 2-nd for loop in multiply_matrices should be
resMatrix[i][j] = 0;
for (k = 0; k < rowsB; k++) // CHANGED to rowsB
resMatrix[i][j] = resMatrix[i][j] + matrix_A[i][k] * matrix_B[k][j];

Answer 2

As pointed out in the comments: You need to seed the rand() function only once. Do srand(time(0)); at the start of your main() function and remove it from elsewhere.
Non-square matrices: There is a bug/typo in multiply_matrices
The line
for (k = 0; k < colsA; k++)
should be
for (k = 0; k < rowsA; k++)