I am trying to create a program to find the transpose of a matrix my dynamic memory allocation. However, while entering the elements of the matrix I can't input more than one element, its only taking the a[0][0] as the input and the program is ending after that.
#include <stdio.h>
#include <stdlib.h>
void createMatrix(int **, int, int);
void inputElements(int **, int, int);
void transpose(int **, int **, int, int);
void display(int **, int, int);
void main()
{
int **matrix, **trans, rows, cols;
printf("\nEnter number of rows in the matrix: ");
scanf("%d", &rows);
printf("\nEnter number of columns in the matrix: ");
scanf("%d", &cols);
createMatrix(matrix, rows, cols);
createMatrix(trans, cols, rows);
inputElements(matrix, rows, cols);
transpose(matrix, trans, rows, cols);
printf("\nMATRIX:\n");
display(matrix, rows, cols);
printf("\nTRANSPOSE OF THE MATRIX:\n");
display(trans, rows, cols);
}
void createMatrix(int **a, int r, int c) //for allocating memory for the matrix
{
int i, j;
a = (int **)malloc(sizeof(int *) * r);
for(i = 0; i < r; i++)
a[i] = (int *)malloc(sizeof(int) * c);
}
void inputElements(int **a, int r, int c) //for entering matrix elements
{
int i, j, t;
for(i = 0; i < r; i++)
{
for(j = 0; j < c; j++)
{
printf("\nEnter matrix element[%d][%d]: ", i + 1, j + 1);
fflush(stdin);
getchar();
scanf("%d", &(a[i][j]));
}
}
}
void transpose(int **a, int **t, int r, int c) //for finding out the transpose of the matrix
{
int i, j;
for (i = 0; i < c; i++)
{
for (j = 0; j < r; j++)
t[i][j] = a[j][i];
}
}
void display(int **a, int r, int c) //for displaying the matrix
{
int i, j;
for (i = 0; i < r; i++)
{
printf("\n");
for (j = 0; j < c; j++)
printf("\t%d", a[i][j]);
}
}
There are many posts about scanf in loops I've seen, but I wasn't able to connect my issue with any of them.
Related
I am writing a program to calculate matrix multiplication but it does not work. When I debug and check each value of the array a and b in function printMatrixMultiplication (which are entered by user), GDB prints out "cannot perform pointer math on incomplete type try casting". (I have searched for it but I still don't get it.) The function only works when the input is predefined in main.
This is my code
#include <stdio.h>
void input(int m, int n, double a[m][n]);
void output(int m, int n, double a[m][n]);
void printMatrixMultiplication(int row_a, int col_a, double a[row_a][col_a], int row_b, int col_b, double b[row_b][col_b]);
int main()
{
int row_a, col_a, row_b, col_b;
// get value of matrix a
printf("row_a = ");
scanf("%d", &row_a);
printf("col_a = ");
scanf("%d", &col_a);
double a[row_a][col_a];
input(row_a, col_a, a);
// output(row_a, col_a, a);
// get value of matrix b
printf("row_b = ");
scanf("%d", &row_b);
printf("col_b = ");
scanf("%d", &col_b);
double b[row_b][col_b];
input(row_b, col_b, a);
// output(row_b, col_b, a);
printMatrixMultiplication(row_a, col_a, a, row_b, col_b, b);
//test
// double a[2][2]={1,2,3,4};
// double b[2][3]={1,2,3,4,5,6};
// printMatrixMultiplication(2,2,a,2,3,b);
return 0;
}
void input(int m, int n, double a[m][n])
{
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
scanf("%lf", &a[i][j]);
}
}
}
void output(int m, int n, double a[m][n])
{
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
printf("%.2f ", a[i][j]);
}
printf("\n");
}
}
void printMatrixMultiplication(int row_a, int col_a, double a[row_a][col_a], int row_b, int col_b, double b[row_b][col_b])
{
if (col_a != row_b)
{
return;
}
double res[row_a][col_b]; //this matrix store results
for (int i = 0; i < row_a; i++) //the values be stored line by line, this
{ //operation is controled by i and j loops.
for (int j = 0; j < col_b; j++) //the k loop helps calculate dot_product.
{
double dot_product = 0;
for (int k = 0; k < col_a; k++)
{
dot_product += a[i][k] * b[k][j]; //ERROR HERE
}
res[i][j] = dot_product;
}
}
output(row_a, col_b, res);
}
So, where does the error come from and how to fix it?
Irrelevant, but the function is not well implemented so if possible, I would really appreciate if anyone gives me a hint to improve it.
I am using GCC version 6.3.0.
It's typo in your code when reading matrix b.
Just replace:
input(row_b, col_b, a);
with
input(row_b, col_b, b);
i am learning pointers and i write these code to add two martix via function, it compile well and give correct answer for 2x2 matrix but for more than two row and col it fails when i try it with 3x3 matrix [0][0] element for the first matrix it automaticaly become 6 and [1][0] it became 9 every time, i can't figure out why this happen
#include <stdio.h>
//-----------------Function------------------
void add(int (*p1)[10], int (*p2)[10], int (*p3)[10], int r, int c);
void get(int (*p1)[10], int r, int c);
void print(int (*p1)[10], int r, int c);
//---------------Main Program----------------
int main()
{
//declartion
int i, j, r, c;
printf("\n\tenter the row and column of matrix\n\t");
scanf("%d %d", &r, &c);
int m1[r][c], m2[r][c], m3[r][c];
printf("\n\tenter the element of first matrix\n\t");
get(m1, r, c);
print(m1, r, c);
printf("\n\tenter the element of second matrix\n\t");
get(m2, r, c);
print(m2, r, c);
add(m1, m2, m3, r, c);
printf("\n");
print(m3, r, c);
return(0);
}
//-------------Define Function---------------
//get()
void get(int (*p1)[10], int r, int c)
{
int i, j;
for(i = 0; i < r; i++)
{
printf("\n\t");
for(j = 0; j < c; j++)
{
scanf("%d", (*(p1+i)+j));
}
}
}
//--------------------X----------------------
//add()
void add(int (*p1)[10], int (*p2)[10], int (*p3)[10], int r, int c)
{
int i, j;
for(i = 0; i < r; i++)
{
for(j = 0; j < c; j++)
{
//printf("\n%d %d = %d & %d", i, j, *(*(p1+i)+j), *(*(p2+i)+j));
*(*(p3+i)+j) = *(*(p1+i)+j) + *(*(p2+i)+j);
}
}
}
//--------------------X----------------------
//print()
void print(int (*p1)[10], int r, int c)
{
int i, j;
for(i = 0; i < r; i++)
{
printf("\n");
for (j = 0; j < c; j++)
{
printf("\t%d", *(*(p1+i)+j));
}
}
}
//--------------------X----------------------
Drop the array pointer notation and the fixed size. Use variable-length arrays based on the parameters.
Remove useless comments like // get ... void get...
Don't use unreadable de-referncing with *(arr+i) when you could be writing readable arr[i].
Print new line after each row, not before each row.
Here's a cleaned up program which compiles. I haven't tested it.
#include <stdio.h>
void add (int r, int c, int p1[r][c], int p2[r][c], int p3[r][c]);
void get (int r, int c, int p1[r][c]);
void print (int r, int c, int p1[r][c]);
int main (void)
{
int i, j, r, c;
printf("\n\tenter the row and column of matrix\n\t");
scanf("%d %d", &r, &c);
int m1[r][c], m2[r][c], m3[r][c];
printf("\n\tenter the element of first matrix\n\t");
get(r, c, m1);
print(r, c, m1);
printf("\n\tenter the element of second matrix\n\t");
get(r, c, m2);
print(r, c, m2);
add(r, c, m1, m2, m3);
printf("\n");
print(r, c, m3);
return(0);
}
void get (int r, int c, int p1[r][c])
{
for(int i = 0; i < r; i++)
{
for(int j = 0; j < c; j++)
{
scanf("%d", &p1[i][j]);
}
}
}
void add (int r, int c, int p1[r][c], int p2[r][c], int p3[r][c])
{
for(int i = 0; i < r; i++)
{
for(int j = 0; j < c; j++)
{
p3[i][j] = p1[i][j] + p2[i][j];
}
}
}
void print (int r, int c, int p1[r][c])
{
for(int i = 0; i < r; i++)
{
for (int j = 0; j < c; j++)
{
printf("\t%d", p1[i][j]);
}
printf("\n");
}
}
I need to do this to persist operations on the matrix as well. Does that mean that it needs to be passed by reference?
Will this suffice?
void operate_on_matrix(char matrix[][20]);
C does not really have multi-dimensional arrays, but there are several ways to simulate them. The way to pass such arrays to a function depends on the way used to simulate the multiple dimensions:
1) Use an array of arrays. This can only be used if your array bounds are fully determined at compile time, or if your compiler supports VLA's:
#define ROWS 4
#define COLS 5
void func(int array[ROWS][COLS])
{
int i, j;
for (i=0; i<ROWS; i++)
{
for (j=0; j<COLS; j++)
{
array[i][j] = i*j;
}
}
}
void func_vla(int rows, int cols, int array[rows][cols])
{
int i, j;
for (i=0; i<rows; i++)
{
for (j=0; j<cols; j++)
{
array[i][j] = i*j;
}
}
}
int main()
{
int x[ROWS][COLS];
func(x);
func_vla(ROWS, COLS, x);
}
2) Use a (dynamically allocated) array of pointers to (dynamically allocated) arrays. This is used mostly when the array bounds are not known until runtime.
void func(int** array, int rows, int cols)
{
int i, j;
for (i=0; i<rows; i++)
{
for (j=0; j<cols; j++)
{
array[i][j] = i*j;
}
}
}
int main()
{
int rows, cols, i;
int **x;
/* obtain values for rows & cols */
/* allocate the array */
x = malloc(rows * sizeof *x);
for (i=0; i<rows; i++)
{
x[i] = malloc(cols * sizeof *x[i]);
}
/* use the array */
func(x, rows, cols);
/* deallocate the array */
for (i=0; i<rows; i++)
{
free(x[i]);
}
free(x);
}
3) Use a 1-dimensional array and fixup the indices. This can be used with both statically allocated (fixed-size) and dynamically allocated arrays:
void func(int* array, int rows, int cols)
{
int i, j;
for (i=0; i<rows; i++)
{
for (j=0; j<cols; j++)
{
array[i*cols+j]=i*j;
}
}
}
int main()
{
int rows, cols;
int *x;
/* obtain values for rows & cols */
/* allocate the array */
x = malloc(rows * cols * sizeof *x);
/* use the array */
func(x, rows, cols);
/* deallocate the array */
free(x);
}
4) Use a dynamically allocated VLA. One advantage of this over option 2 is that there is a single memory allocation; another is that less memory is needed because the array of pointers is not required.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
extern void func_vla(int rows, int cols, int array[rows][cols]);
extern void get_rows_cols(int *rows, int *cols);
extern void dump_array(const char *tag, int rows, int cols, int array[rows][cols]);
void func_vla(int rows, int cols, int array[rows][cols])
{
for (int i = 0; i < rows; i++)
{
for (int j = 0; j < cols; j++)
{
array[i][j] = (i + 1) * (j + 1);
}
}
}
int main(void)
{
int rows, cols;
get_rows_cols(&rows, &cols);
int (*array)[cols] = malloc(rows * cols * sizeof(array[0][0]));
/* error check omitted */
func_vla(rows, cols, array);
dump_array("After initialization", rows, cols, array);
free(array);
return 0;
}
void dump_array(const char *tag, int rows, int cols, int array[rows][cols])
{
printf("%s (%dx%d):\n", tag, rows, cols);
for (int i = 0; i < rows; i++)
{
for (int j = 0; j < cols; j++)
printf("%4d", array[i][j]);
putchar('\n');
}
}
void get_rows_cols(int *rows, int *cols)
{
srand(time(0)); // Only acceptable because it is called once
*rows = 5 + rand() % 10;
*cols = 3 + rand() % 12;
}
(See srand() — why call it only once?.)
Easiest Way in Passing A Variable-Length 2D Array
Most clean technique for both C & C++ is: pass 2D array like a 1D array, then use as 2D inside the function.
#include <stdio.h>
void func(int row, int col, int* matrix){
int i, j;
for(i=0; i<row; i++){
for(j=0; j<col; j++){
printf("%d ", *(matrix + i*col + j)); // or better: printf("%d ", *matrix++);
}
printf("\n");
}
}
int main(){
int matrix[2][3] = { {0, 1, 2}, {3, 4, 5} };
func(2, 3, matrix[0]);
return 0;
}
Internally, no matter how many dimensions an array has, C/C++ always maintains a 1D array. And so, we can pass any multi-dimensional array like this.
I don't know what you mean by "data dont get lost". Here's how you pass a normal 2D array to a function:
void myfunc(int arr[M][N]) { // M is optional, but N is required
..
}
int main() {
int somearr[M][N];
...
myfunc(somearr);
...
}
2D array:
int sum(int array[][COLS], int rows)
{
}
3D array:
int sum(int array[][B][C], int A)
{
}
4D array:
int sum(int array[][B][C][D], int A)
{
}
and nD array:
int sum(int ar[][B][C][D][E][F].....[N], int A)
{
}
I feel like I've attempted every combination I know of to get this to work and can't figure it out. How can I scanf() into an int** passed as a pointer to a function? I tried searching but couldn't find this, if it's a duplicate please let me know and I'll delete. It begins to run and after entering a few values it segfaults.
Here's my code, I think it's messing up on the scanf() line of the setMatrix() function:
#include <stdio.h>
#include <stdlib.h>
// create zero initialized matrix
int** callocMatrix(int rmax, int colmax) {
int **mat = calloc(rmax, sizeof(int*));
for(int i = 0; i < rmax; i++) mat[i] = calloc(colmax, sizeof(int));
return mat;
}
// fill matrix
void setMatrix(int ***mat, int r, int c){
printf("Insert the elements of your matrix:\n");
for (int i = 0; i < r; i++) {
for (int j = 0; j < c; j++) {
printf("Insert element [%d][%d]: ", i, j);
scanf("%d", mat[i][j]); // problem here??
printf("matrix[%d][%d]: %d\n", i, j, (*mat)[i][j]);
}
}
return;
}
// print matrix
void printMatrix(int ***mat, int r, int c){
for (int i=0; i<r;i++){
for (int j=0; j<c;j++) {
printf("%d ", (*mat)[i][j]);
}
printf("\n");
}
}
int main(int argc, char *argv[]) {
int r = 3, c = 3;
int **mat = callocMatrix(r, c);
setMatrix(&mat, r, c);
printMatrix(&mat, r, c);
}
There is no need to use triple pointer ***. Passing two-dimensional array will work as is. Here is the code:
#include <stdio.h>
#include <stdlib.h>
// create zero initialized matrix
int** callocMatrix(int rmax, int colmax) {
int **mat = calloc(rmax, sizeof(int*));
for(int i = 0; i < rmax; i++) mat[i] = calloc(colmax, sizeof(int));
return mat;
}
// fill matrix
void setMatrix(int **mat, int r, int c){
printf("Insert the elements of your matrix:\n");
for (int i = 0; i < r; i++) {
for (int j = 0; j < c; j++) {
printf("Insert element [%d][%d]: ", i, j);
scanf("%d", &mat[i][j]); // no problem here
printf("matrix[%d][%d]: %d\n", i, j, mat[i][j]);
}
}
}
// print matrix
void printMatrix(int **mat, int r, int c){
for (int i=0; i<r;i++){
for (int j=0; j<c;j++) {
printf("%d ", mat[i][j]);
}
printf("\n");
}
}
int main(int argc, char *argv[]) {
int r = 3, c = 3;
int **mat = callocMatrix(r, c);
setMatrix(mat, r, c);
printMatrix(mat, r, c);
}
Should be:
scanf("%d", &(*mat)[i][j]);
You're passing a pointer to you matrix object, so you need to dereference it (with *) just as you do with printf. scanf then needs the address of the element to write into, so you need the &
I have an issue passing a matrix to a function in C. There is the function I want to create:
void ins (int *matrix, int row, int column);
but I noticed that in contrast to the vectors, matrix give me an error. How can I pass my matrix to a function so?
EDIT --> there is the code:
// Matrix
#include <stdio.h>
#define SIZE 100
void ins (int *matrix, int row, int column);
void print (int *matrix, int row, int column);
int main ()
{
int mat[SIZE][SIZE];
int row, col;
printf("Input rows: ");
scanf ("%d", &row);
printf("Input columns: ");
scanf ("%d", &col);
printf ("Input data: \n");
ins(mat, row, col);
printf ("You entered: ");
print(mat, row, col);
return 0;
}
void ins (int *matrix, int row, int column);
{
int i, j;
for (i = 0; i < row; i++)
{
for (j = 0; j < column; j++)
{
printf ("Row %d column %d: ", i+1, j+1);
scanf ("%d", &matrix[i][j]);
}
}
}
void print (int *matrix, int row, int column)
{
int i;
int j;
for(i=0; i<row; i++)
{
for(j=0; j<column; j++)
{
printf("%d ", matrix[i][j]);
}
printf("\n");
}
}
You need to pass a pointer with as much levels of indirection (*) as the number of dimensions of your matrix.
For example, if your matrix is 2D (e.g. 10 by 100), then:
void ins (int **matrix, int row, int column);
If you have a fixed dimension (e.g. 100), you can also do:
void ins (int (*matrix)[100], int row, int column);
or in your case:
void ins (int (*matrix)[SIZE], int row, int column);
If both your dimensions are fixed:
void ins (int matrix[10][100], int row, int column);
or in your case:
void ins (int matrix[SIZE][SIZE], int row, int column);
If you have a modern C compiler you can do the following for 2D matrices of any sizes
void ins (size_t rows, size_t columns, int matrix[rows][columns]);
Important is that the sizes come before the matrix, such that they are known, there.
Inside your function you then can access the elements easily as matrix[i][j] and the compiler is doing all the index calculations for you.
it would also possible to leave the first dimension empty, the same as (*matrix):
void ins (int matrix[][100], int row, int column);
Much better way to use malloc function and create dynamically allocated array and do whatever you want to do using 2d array:
#include <stdio.h>
#include <stdlib.h>
#include <stdio.h>
void fun(int **arr,int m,int n)
{
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
scanf("%d", &arr[i][j]);
}
}
}
int main()
{
int i,j,m,n;
printf("enter order of matrix(m*n)");
scanf("%d*%d",&m,&n);
int **a=(int **)malloc(m*sizeof(int));
for(i=0;i<n;i++)
a[i]=(int *)malloc(n*sizeof(int));
fun(a,m,n);
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
printf("%d ", a[i][j]);
}
printf("\n");
}
return 0;
}
output:
#include <stdio.h>
#include <stdlib.h>
#include <stdio.h>
void fun(int **arr,int m,int n)
{
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
scanf("%d", &arr[i][j]);
}
}
}
int main()
{
int i,j,m,n;
printf("enter order of matrix(m*n)");
scanf("%d*%d",&m,&n);
int **a=(int **)malloc(m*sizeof(int));
for(i=0;i<n;i++)
a[i]=(int *)malloc(n*sizeof(int));
fun(a,m,n);
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
printf("%d ", a[i][j]);
}
printf("\n");
}
return 0;
}
You can try this as well:
void inputmat(int r,int c,int arr[r * sizeof(int)][c * sizeof(int)])