#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(){
int N;
scanf("%d", &N);
int **arr;
arr = (int**)malloc(sizeof(int) * N);
for(int i = 0; i < N; i++){
arr[i] = (int*)malloc(sizeof(int) * N);
}
for(int i = 0; i < N; i++){
for(int j = 0; j < N; j++){
if(i == 0 || j == 0)
arr[i][j] = 1;
else
arr[i][j] = arr[i - 1][j] + arr[i][j - 1];
}
}
for(int i = 0; i < N; i++){
for(int j = 0; j < N; j++){
printf("%d ", arr[i][j]);
}
printf("\n");
}
for(int i = 0; i < N; i++)
free(arr[i]);
free(arr);
return 0;
}
This code makes a 2-dimensional array with a pointer; I want assign value arr[i][j] = 1. However, an error EXC_BAD_ACCESS occurs in XCode on a Mac. I don't know how to solve the problem. What is my mistake? The assigning for loop is where the trouble occurs.
Related
I need to multiply two square matrixes A and B 15x15.
Unfortunately, I'm getting this kind of error.
I know the problem is in pointers while calculating matrix C.
C[i][j] += *(A + k) * *(B + k)
I hope you can explain me what's wrong. I'm a beginner xD.
Thank you in advance.
#include <stdio.h>
#define N 15
#define _CRT_SECURE_NO_WARNINGS
int main() {
int A[N][N];
int B[N][N];
int C[N][N];
printf("Input matrix A.\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("Enter your element:\n");
scanf_s("%d", &A[i][j]);
}
printf("\n");
}
printf("Input matrix B.\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("Enter your element:\n");
scanf_s("%d", &B[i][j]);
}
printf("\n");
}
printf("Matrix A.\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("%d\t", A[i][j]);
}
printf("\n");
}
printf("Matrix B.\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("%d\t", B[i][j]);
}
printf("\n");
}
for (int i = 0; i < 15; i++) {
for (int j = 0; j < 15; j++) {
C[i][j] = 0;
for (int k = 0; k < 14; k++) {
C[i][j] += *(A + k) * *(B + k);
k++;
}
}
}
printf("Your result:\n");
printf("Matrix C.\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("%d\t", C[i][j]);
}
printf("\n");
}
return 0;
}
The problem in the multiplication is that A+k and B+k have type int (*)[15] which means dereferencing it once only makes a pointer out of them; furthermore, you need to take row and column items individually, which means A[i][k] and B[k][j], right? (also, there's no point on using confusing syntax, as the underlying operation is exactly the same).
Here's a fixed and improved version:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#define N 15
/* Improvement 1 (type abstraction) */
typedef int NxN_int_matrix[N][N];
/* Improvement 2 (input function & wrapper) */
#define input_matrix(var) input_matrix_ex((var), #var)
static void input_matrix_ex(NxN_int_matrix dst, char *name)
{
printf("Input matrix %s.\n", name);
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
/* Improvement 3 (nicer prompt) */
printf("%s[%2d][%2d]: ", name, i, j);
fflush(stdout);
scanf_s("%d", &dst[i][j]);
}
}
printf("\n");
}
/* Improvement 4 (print function) */
#define print_matrix(var) print_matrix_ex(#var, (var))
static void print_matrix_ex(char *name, NxN_int_matrix M)
{
printf("Matrix %s.\n", name);
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("%d\t", M[i][j]);
}
printf("\n");
}
}
/* Improvement 5 (move multiplication to a function too, and fix it) */
static void mult_matrix(NxN_int_matrix dst, NxN_int_matrix a, NxN_int_matrix b)
{
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
/* Improvement 6 (don't write out intermediate values) */
int tmp = 0;
for (int k = 0; k < N; k++)
tmp += a[i][k] * b[k][j];
dst[i][j] = tmp;
}
}
}
int main()
{
NxN_int_matrix A, B, C;
input_matrix(A);
input_matrix(B);
print_matrix(A);
print_matrix(B);
mult_matrix(C, A, B);
printf("Your result:\n");
print_matrix(C);
return 0;
}
/* Possible further improvements:
* - using a transposed B might make multiplication faster
*/
I have a 2d array filled with 0's and i'm trying to fill the main diagonal with numbers from 1 to n, this is the main code:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main()
{
srand(time(NULL));
int m, n, i, j;
printf("Number of rows and columns:");
scanf("%d", &n);
int a[n][n];
for (i = 0; i < n; i++)
for(j = 0; j < n; j++)
a[i][j] = rand() % 1;
printf("The matrix is:\n");
for (i = 0; i < n; i++)
{
printf(" \n ");
for(j = 0; j < n; j++)
{
printf(" %d\t ", a[i][j]);
}
}
}
What I've tried to do is to fill the diagonal manually, but that's not what I want to do. I want to make it fill itself automatically. I need to do it without using any functions.
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
arr[i][j] = ((i == j) * (i + 1));
}
}
The simplest way is to add this part after you fill the matrix with zeros.
for (i = 0; i < n; i++)
arr[i][i] = i + 1;
Suppose in Gauss Elimination Method the first value of matrix, A[0][0]=0
Then how can I swap row 1 of matrix "A" with row 2, so that i get the correct result ?
Assuming a simpel 2d-array build the way as shown below: just exchange the rows.
#include <stdio.h>
#include <stdlib.h>
#define S_MATRIX_DIM 5
int main()
{
int **A;
int *tmp;
int i, j, entry;
entry = 0;
A = malloc(S_MATRIX_DIM * sizeof(int *));
for (i = 0; i < S_MATRIX_DIM; i++) {
A[i] = malloc(S_MATRIX_DIM * sizeof(int));
for (j = 0; j < S_MATRIX_DIM; j++) {
A[i][j] = entry++;
}
}
puts("Matrix A =");
for (i = 0; i < S_MATRIX_DIM; i++) {
for (j = 0; j < S_MATRIX_DIM; j++) {
printf("%d,", A[i][j]);
}
putchar('\n');
}
tmp = A[0];
A[0] = A[1];
A[1] = tmp;
puts("Matrix A, row exchanged =");
for (i = 0; i < S_MATRIX_DIM; i++) {
for (j = 0; j < S_MATRIX_DIM; j++) {
printf("%d,", A[i][j]);
}
putchar('\n');
}
for (i = 0; i < S_MATRIX_DIM; i++) {
free(A[i]);
}
free(A);
exit(EXIT_SUCCESS);
}
keep a temp value from the same type;
swap value by value,
example:
temp=a[i][j];
a[i][j]=a[i+1][j];
a[i+1][j]=temp;
I am trying to send a pointer of a matrix to function for printing the values. However, my following code prints some long numbers so I assumed it prints the addresses instead! How can I print the value of the matrix after passing the pointer of it?
#include <stdio.h>
#include <string.h>
#include <math.h>
void printing(int *edge);
void main(){
int N=3;
int i,j;
int *edge[N];
for (i = 0; i < N; i++){
*(edge+i) = (int *)malloc(N * sizeof(int));
}
srand(0);
for(i = 0; i < N; i++){
for(j = 0; j < N; j++){
if(i == j)
*(*(edge+i)+j) = 0;
else
*(*(edge+i)+j) = 1; //rand() % 10;
}
}
printing(edge); // Pass the pointer of the matrix
}
void printing(int *edge){
int i,j;
int N= 3;
for( i = 0; i < N; i++){
for(j = 0; j < N; j++){
printf("%d \t", ((edge+i)+j)); // I think I have to do something in this line.
}
printf("\n");
}
}
The parameter type of printing is incorrect. It should be int *edge[]. Then when you print, use *(*(edge+i)+j), or better yet edge[i][j].
The result:
void printing(int *edge[]){
int i,j;
int N = 3;
for( i = 0; i < N; i++){
for(j = 0; j < N; j++){
printf("%d \t", edge[i][j]);
}
printf("\n");
}
}
Also, be sure to #include <stdlib.h>, as it's needed for malloc and srand.
To access any element I use *(Ptr + i).
Is there any way to put 2D array into the allocated memory in order to access any element using array[i][j]?
Here is the code:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int *Ptr;
Ptr = malloc(M*N*sizeof(int));
for (i = 0; i <= M * N; i++)
*(Ptr + i) = 1 + rand()%10;
return 0;
}
Sample
#include <stdio.h>
#include <stdlib.h>
#define N 4
#define M 3
int main()
{
int *Ptr;
int (*p)[M];
int i,j;
Ptr = malloc(M*N*sizeof(int));
for (i = 0; i < M * N; i++){
*(Ptr + i) = 1 + rand()%10;
// printf("%d ", Ptr[i]);
}
// printf("\n");
p=(int (*)[M])Ptr;//p[N][M]
for(i = 0; i < N ;++i){
for(j = 0; j < M;++j)
printf("%d ", p[i][j]);
printf("\n");
}
return 0;
}
Try this:
int** theArray;
theArray = (int**) malloc(M*sizeof(int*));
for (int i = 0; i < M; i++)
{
theArray[i] = (int*) malloc(N*sizeof(int));
}
Sample:
int M = 5;
int N = 5;
int** theArray = (int**) malloc(M*sizeof(int*));
for (int i = 0; i < M; i++)
{
theArray[i] = (int*) malloc(N*sizeof(int));
for(int j = 0 ; j < N; j++)
{
theArray[i][j] = i+j;
printf("%d ", theArray[i][j]);
}
printf("\n");
}
for (int k = 0; k < M; k++)
{
free(theArray[k]);
}
free(theArray);