Transpose a matrix via pointer in C - c

Question

I'm trying to transpose a matrix in C while passing the matrix to a function and return a pointer to a transposed matrix. What am I doing wrong in the second while loop?
in main
ptr = (float *) getMatrix(numRowsB, numColsB);
transposePtr = transpose(ptr, numRowsB, numColsB);
printf("\nBtranspose =\n");
printMatrix(transposePtr, numColsB, numRowsB);
create matrix
float* getMatrix(int n, int m)
{
int i, j;
float *arrayPtr;
if ((n <= 0) || (m <= 0))
{
printf("function getMatrix(): matrix dimensions are invalid\n");
return NULL;
}
arrayPtr = (float *) malloc(n*m*sizeof(float));
if(arrayPtr == NULL)
{
printf("function getMatrix: Unable to malloc array\n");
return NULL;
}
transpose function
float* transpose(float *matrix, int n, int m)
{
int i = 0;
int j = 0;
float num;
float *transposed=(int*) malloc(sizeof(int)*n*m);
while(i < n-1)
{
while(j < m-1)
{
num = *(matrix+i*m+j);
*(transposed+j*m+i)= num;
j++;
}
i++;
}
return transposed;
}
print fucntion
void print(float *matrix, int n, int m)
{
int i = 0;//row counter
int j = 0;//col counter
for(i = 0; i < n; i++){
printf("\n");
for(j = 0; j < m; j++){
printf("%f ", *(matrix + i*n + j));
}
}
}
Example input:
1 2 3
4 5 6
Output:
1.000000 0.000000
2.000000 3396.580087
-0.000000 0.000000

Answer 1

Part of the problem was your print function
Here is a version of your functions that works:
float* transpose(float *matrix, int n, int m)
{
int i = 0;
int j = 0;
float num;
float *transposed=malloc(sizeof(float)*n*m);
while(i < n) {
j = 0;
while(j < m) {
num = *(matrix + i*m + j);
*(transposed + i+n*j) = num; // I changed how you index the transpose
j++;
}
i++;
}
return transposed;
}
void print(float *matrix, int n, int m)
{
int i = 0;//row counter
int j = 0;//col counter
for(i = 0; i < n; i++){
printf("\n");
for(j = 0; j < m; j++){
printf("%f ", *(matrix + i*m + j)); // Changed from n to m
}
}
}
There were a few things.
Use sizeof(float) instead of sizeof(int)
Your loop should be i < n and j < m instead of i < n-1 and j < m-1 and finally you need to reset j to zero every time
The matrix indexes in inner most loop of your transpose function was incorrect
Your print function was using the wrong variable in the multiplication
Also it is generally considered bad practice to cast the result of malloc in C.