I am new to StackOverflow. I'm sorry if I can't express myself that well, but I think I found the solution to your problem.
Let's look at this step-by-step.
- When passing an array to a function, you do not need to write the subscripts.
That means that instead of this:
readMatrix(&arrA[3][4]);
Just write this:
readMatrix(arrA);
You can (actually, should) also remove the pointer operator (&) because when only the array name is used, it acts as a pointer automatically.
Let's now take a look at the definition of readMatrix.
int *readMatrix(int *arr)
Using pointers for multi-dimensional arrays is okay, but the compiler would spit out a lot of warnings.
The most standard way is using subscripts in the definition of the function:
int *readMatrixStandard(int arr[3][4])
{
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 4; ++j)
{
printf("row %d, col %d: ", i + 1, j + 1);
scanf("%d", &arr[i][j]);
}
}
printf("\n");
return arr;
}
- The subscripts in subM
For your case, there are two ways to access a multi-dimensional array.
Either tell the compiler that this function takes an multi-dimensional array:
Instead of this:
int *subM(int *arrA, int*arrB, int *arrC)...
Do this:
int *subM(int arrA[3][4], int arrB[3][4], int arrC[3][4])...
The code would then look something like this:
int *subMMultiDimension(int arrA[3][4], int arrB[3][4], int arrC[3][4]){
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 4; ++j)
{
//printf("row %d, col %d: ", i + 1, j + 1);
arrC[i][j] = arrA[i][j] - arrB[i][j]; //code where I am getting error
printf("%5d", arrC[i][j]);
}
puts(""); // for newline
}
return arrC;
}
Or use some pointer magic that is exclusive to C/C++ :) (not to be combined with the solution above)
Instead of this:
int *subM(int *arrA, int*arrB, int *arrC){
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 4; ++j)
{
//printf("row %d, col %d: ", i + 1, j + 1);
&arrC[i][j] = &arrA[i][j] - &arrB[i][j]; //code where I am getting error
}
}
return arrC;
}
Try this:
int *subM(int *arrA, int *arrB, int *arrC){
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 4; ++j)
{
//printf("row %d, col %d: ", i + 1, j + 1);
arrC[i * 4 + j] = arrA[i * 4 + j] - arrB[i * 4 + j]; //code where I am getting error
}
}
return arrC;
}
Use one of the ways, but the first one seems to be more standard because the compiler doesn't throw warnings on the first one.
- Return value
You probably see where this is going. I'm just slapping on the code now.
Instead of:
return arr;
return arrC;
I prefer this for less warnings:
return arr[0];
return arrC[0];
The reason is simple. It points pratically to the same address, but it lets the compiler keep the mouth shut.
I think that this was it. The final code would look like this:
#include <stdio.h>
int * readMatrixStandard(int arr[3][4])
{
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 4; ++j)
{
printf("row %d, col %d: ", i + 1, j + 1);
scanf("%d", &arr[i][j]);
}
}
printf("\n");
return arr[0];
}
int * subMMultiDimension(int arrA[3][4], int arrB[3][4], int arrC[3][4])
{
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 4; ++j)
{
//printf("row %d, col %d: ", i + 1, j + 1);
arrC[i][j] = arrA[i][j] - arrB[i][j]; //code where I am getting error
printf("%5d", arrC[i][j]);
}
puts(""); // for newline
}
return arrC[0];
}
int main(void) // I recommend to always write void here if you are not using
// an old compiler
{
int arrA[3][4];
int arrB[3][4];
int arrC[3][4];
readMatrixStandard(arrA);
readMatrixStandard(arrB);
subMMultiDimension(arrA,arrB,arrC);
return 0;
}
Compiles nicely without warnings.
These code snippets are just my recommendations. If you want to know the most standard way to do something in C, you will probably have to look it up. A good book is also recommended. For instance, I learnt C with C Primer Plus by Stephen Prata. A great book with a lot of examples and illustrations to help you understand the situation.
Sorry again for my English. Guess there is still a long way to go.
If I missed anything or made a mistake somewhere, please let me know.
Edit: It's Stephen Prata, not Stephan ;)
