I have two 2d arrays "a", "b" (empty array) with the same size, I have to change "a" due to a certain function that save it's new values in "b", then I have to change the new values according to the same function, so the program will save b's new values in a and then back to a.
When the arrays are printed only the first two ones are printed!!
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define MSIZE 10
void new_gen(char * a[MSIZE],int s,char** b); /*the function we talked about*/
void print_m(char** b,int s); /*prints matrix*/
void cpy_m(char** b, char** a, int s);
int main()
{
int Size, gen, i, j;
printf("Enter number of generations\t");
scanf("%d", &gen);
printf("\nEnter size of the matrix (max size is %d and min is 2)\t", MSIZE);
scanf("%d", &Size);
char **m = (char**) malloc(Size*sizeof(char*));
for (i=0; i<Size; i++)
{
m[i] = (char*) malloc(Size*sizeof(char));
}
printf("Enter matrix of first generation\n");
for (i=0; i<Size; i++) {
for (j=0; j<Size; j++) {
scanf(" %c", &m[i][j]);
}
}
print_m(m, Size);
for (i=1; i<gen; i++)
{
char **n = (char**) malloc(Size*sizeof(char*));
for (i=0; i<Size; i++)
{
n[i] = (char*) malloc(Size*sizeof(char));
}
new_gen(m, Size, n);
print_m(n, Size);
cpy_m(n, m, Size);
}
return 0; }
void print_m(char** b, int s)
{
int i, j;
putchar('\n');
for (i=0; i<s; i++)
{
for (j=0; j<s; j++) {
printf("%c", *(*(b+i)+j));
}
putchar('\n');
}
return;
}
void cpy_m(char* b[MSIZE],char** a, int s)
{
int i, j;
for (i=0; i<s; i++) {
for (j=0; j<s; j++) {
*(*(a+i)+j) = b[i][j];
}
return;
}}
Consider this pair of nested loops
for (i=1; i<gen; i++)
{
char **n = (char**) malloc(Size*sizeof(char*));
for (i=0; i<Size; i++)
{
n[i] = (char*) malloc(Size*sizeof(char));
}
new_gen(m, Size, n);
print_m(n, Size);
cpy_m(n, m, Size);
}
First point, both the loops use i as the control variable, but they are nested.
Second point, you overwrite the pointers from malloc in each iteration (there is no free).
Related
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 need that vector_total dont have any repeated number.
Function for entry vector1 and vector2 that are declared in main().
void entrada_vectors(int vector1[], int vector2[], int vector_total[], int *n, int *m)
{
int i=0, j=0;
/*Entrarem els nombres del vector 1 primer */
for (i=0; i<*n; i++)
{
vector_total[i]=vector1[i];
}
/*Entrarem els nombres del vector 2 després */
for (i=*n; i<*n+*m; i++)
{
if (j<*m)
{
vector_total[i]=vector2[j];
j++;
}
}
}
Function 2. This is for order numbers in vector_total.
void ordena(int vector_total[], int *n, int *m)
{
int i=0, j=0;
int aux=0;
for (i=0; i<*n+*m-1; i++)
{
for (j=0; j<*n+*m-1; j++)
{
if (vector_total[j]>vector_total[j+1])
{
aux=vector_total[j];
vector_total[j]=vector_total[j+1];
vector_total[j+1]=aux;
aux=0;
}
}
}
}
Function 3. Print vector_total
void mostra(int vector_total[], int *n, int *m )
{ int i;
for (i=0; i<*n+*m; i++)
{
printf ("Pos %d del vector: %d\n", i, vector_total[i] );
}
}
Function 4. Here are the problem!! This function is for clean my vector_total and drop the repeated numbers.
void limpiar_repetidos(int vector_total[], int *n, int *m)
{
int x=0, i=0, j=0;
for (i=0; i<*n+*m-1; i++)
{
for (j=0; j<*n+*m-1; j++)
{
if (vector_total[j]==vector_total[j+1])
{
x=j+1;
for (i=*n+*m; i>x; i--)
{
vector_total[i-1]=vector_total[i];
}
}
}
}
}
And here is my main. And my declaration variables:
int vector1[]={7,1,5,3,4,2};
int vector2[]={3,7,3,0,9,10};
int n=sizeof(vector1)/sizeof(vector1[0]);
int m=sizeof(vector2)/sizeof(vector2[0]);
int vector_total[n+m];
main()
{
entrada_vectors(vector1, vector2, vector_total, &n, &m);
ordena(vector_total, &n, &m);
mostra(vector_total, &n, &m);
limpiar_repetidos(vector_total, &n, &m);
printf ("==================\n");
mostra(vector_total, &n, &m);
return 0;
}
Thanks everybody! :)
1) If function deal with only a vector_total , Length of the vector_total is better to pass by one argument. Also you do not need to pointer pass if it will not change.
void mostra(int vector_total[], int len){
int i;
for (i=0; i<len; i++) {
printf ("Pos %d del vector: %d\n", i, vector_total[i] );
}
}
2) function need a new length after the element has been removed. Also, deletion of adjacent same elements that can be like this.
int limpiar_repetidos(int vector_total[], int len){//int *n, int *m --> int len
int i, size, new_size;
size = len;
for(i = new_size = 1; i < size; ++i){
if(vector_total[new_size-1] != vector_total[i])
vector_total[new_size++] = vector_total[i];
}
return new_size;
}
Example of use
mostra(vector_total, m + n);
int l = limpiar_repetidos(vector_total, n + m);
mostra(vector_total, l);
I am supposed to build a matrix_mul function that display the result of a multiplication between two matrices that were created via a struct. My problem is, my function does not multiply the value inside the matrices instead it return an interger.
#include<stdio.h>
#include<stdlib.h>
typedef struct{
int rows;
int cols;
int **data;
} matrix;
matrix matrix_mul(int **a, int **b){
int rowA=(sizeof(a)/sizeof(a[0]));
int colA=(sizeof(a)/sizeof(a[0][0]))/rowA;
int rowB=(sizeof(b)/sizeof(b[0]));
int colB=(sizeof(b)/sizeof(b[0][0]))/rowB;
int i, j, **mulMatrix;
if(colA != rowB)
printf("error: cannot multiply matrices");
else{
int i, j, k;
mulMatrix = (int **)malloc(rowA * sizeof(int *));
for(i=0; i<rowA; i++)
mulMatrix[i] = (int *)malloc(colB * sizeof(int));
for(i=0; i<rowA; ++i){
for(j=0; j<colB; ++j){
for(k=0; k<colA; ++k)
{
mulMatrix[i][j]+= a[i][k] * b[k][j];
}
}
}
}
printf("Matrix: \n\n");
for(i=0; i< rowA; i++){
for(j=0; j< colB; j++){
printf("%d ", mulMatrix[i][j]);
}
printf("\n\n");
}
}
int main()
{
int i, j;
matrix a, b;
printf("matrix1 - enter number of rows and cols: ");
scanf("%d %d", &a.rows, &a.cols);
a.data = (int **)malloc(a.rows * sizeof(int *));
printf("enter matrix values: ");
for(i=0; i<a.rows; i++){
a.data[i] = (int *)malloc(a.cols * sizeof(int));
for(j=0; j<a.cols; j++){
scanf("%d", &a.data[i][j]);
}
}
printf("matrix2 - enter number of rows and cols: ");
scanf("%d %d", &b.rows, &b.cols);
b.data = (int **)malloc(b.rows * sizeof(int *));
printf("enter matrix values: ");
for(i=0; i<b.rows; i++){
b.data[i] = (int *)malloc(b.cols * sizeof(int));
for(j=0; j<b.cols; j++){
scanf("%d", &b.data[i][j]);
}
}
matrix_mul(a.data, b.data);
return 0;
}
These lines
int rowA=(sizeof(a)/sizeof(a[0]));
int colA=(sizeof(a)/sizeof(a[0][0]))/rowA;
won't give you the results you are looking for.
sizeof(a) is sizeof(int**) and sizeof(a[0]) is sizeof(int*). Since pointers are usually of the same size, rowA will be always set to 1. colA will be set to sizeof(int**)/sizeof(int), which is a constant value. Once again, it's not the value you are hoping to get.
You should pass the matrix objects, a and b to matrix_mul. That'll give you the size of the matrices to use for multiplying them.
matrix matrix_mul(matrix a, matrix b){
Of course, you need to modify the implementation accordingly.
I don't have a lot of experience with pointers, but I want to try to make an array of pointers, each pointer pointing to a scanned string.
For example, you first input how many strings you want to scan (for example 5), and then I want to scan those strings and make an array of 5 pointers that point to those strings.
Because I didn't have a lot experience with something like this, I first tried it with normal arrays instead of strings, what I got is this:
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<assert.h>
int **array(int m, int n) {
int i, j;
int **array = malloc(n*sizeof(int*));
for (j=0; j<m; j++) {
for (i=0; i<n; i++) {
array[i]=malloc(m * sizeof(int));
scanf("%d", &array[j][i]);
printf("array[%d][%d] is scanned and has value %d\n", j, i, array[j][i]);
}
}
return array;
}
int main(int argc, char*argv[]){
int m, n, *p, k;
scanf("%d %d", &m, &n);
printf("m is %d and n is %d\n", m, n);
p=*array(m, n);
printf("the numbers are:\n");
for (k=0; k<m*n; k++) {
printf("%d\n", p[k]);
}
return 0;
}
But here it's already going wrong, and I don't know why...
At the last printf, I always get wrong numbers, 0's and 17's...
Can someone explain me why this is and what I'm doing wrong? I think it's something with the returning of the array but I'm not sure..
If someone could explain this to me it would be great.
The problem with your code is the following:
// m = 3, n = 5
// array = ptr1, ptr2, ptr3, ptr4, ptr5
// | |
// 3 ints |
// 3 ints ..
int **array(int m, int n) {
int i, j;
int **array = (int**)malloc(n*sizeof(int*));
for (j=0; j<m; j++) {
for (i=0; i<n; i++) {
array[i]=(int*)malloc(m * sizeof(int));
scanf("%d", &array[j][i]);
printf("array[%d][%d] is scanned and has value %d\n", j, i, array[j][i]);
}
}
return array;
}
In the above example (m=3, n=5) you allocated 5 pointers to integers and then tried to populate them by allocating memory at each iteration in the inner-loop (WRONG). If you allocate new memory at each iteration, you're gonna lose the pointer to the previously allocated memory and the data you stored!
Plus the indices seem to be wrong for the inner and outer loop, a correct version of your code is:
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<assert.h>
// 3, 5
// array = ptr1, ptr2, ptr3, ptr4, ptr5
// | |
// 3 ints |
// 3 ints ..
int **array(int m, int n) {
int i, j, index;
int **array = (int**)malloc(n*sizeof(int*));
index = 0;
for (j=0; j<n; j++) {
array[j]=(int*)malloc(m * sizeof(int)); // Allocate once per each j
for (i=0; i<m; i++) {
array[j][i] = index++;
printf("array[%d][%d] is scanned and has value %d\n", j, i, array[j][i]);
}
}
return array;
}
int main(int argc, char*argv[]){
int m, n, **p, k, i, j;
m = 3;
n = 5;
printf("m is %d and n is %d\n", m, n);
p=array(m, n);
printf("the numbers are:\n");
for (j=0; j<n; j++)
for(i=0; i<m; i++)
printf("%d\n", p[j][i]);
return 0;
}
And the above version is STILL NOT CORRECT : You need to free the allocated memory!
I'll leave that as an exercise.. hint: you CAN'T simply do "free(p);" :]
Are you sure about this for loop? If you've the malloc inside the inner loop you're not creating a matrix because every time you override the same cells...
int i, j;
int **array = malloc(n*sizeof(int*));
for (j=0; j<m; j++) {
for (i=0; i<n; i++) {
array[i]=malloc(m * sizeof(int));
scanf("%d", &array[j][i]);
printf("array[%d][%d] is scanned and has value %d\n", j, i, array[j][i]);
}
}
It should be something like:
int i, j;
int **array = malloc(n*sizeof(int*));
for (i=0; i<n; i++) {
array[i]=malloc(m * sizeof(int));
for (j=0; j<m; j++) {
scanf("%d", &array[i][j]);
printf("array[%d][%d] is scanned and has value %d\n", i, j, array[i][j]);
}
}
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<assert.h>
void *array(int m, int n) {
int i, j;
int (*array)[n] = malloc(sizeof(int [m][n]));//m*n*sizeof(int)
for (j=0; j<m; j++) {
for (i=0; i<n; i++) {
scanf("%d", &array[j][i]);
printf("array[%d][%d] is scanned and has value %d\n", j, i, array[j][i]);
}
}
return array;
}
int main(int argc, char*argv[]){
int m, n, *p, k;
scanf("%d %d", &m, &n);
printf("m is %d and n is %d\n", m, n);
p=(int*)array(m, n);
printf("the numbers are:\n");
for (k=0; k<m*n; k++) {
printf("%d\n", p[k]);
}
return 0;
}
#include <stdlib.h>
#include <stdio.h>
char **array(int m, int n) {
int i;
char **array = malloc(m*sizeof(char*));
for (i=0; i<m; ++i) {
array[i] = malloc(n*sizeof(char));//Fixed length : like char array[m][n] (char *array[m])
scanf("%s", array[i]);//!! There is no length constraints.
printf("array[%d] is scanned and has value %s\n", i, array[i]);
}
return array;
}
int main(int argc, char*argv[]){
int m, n, k;
char **p;
scanf("%d %d", &m, &n);
printf("m is %d and n is %d\n", m, n);
p=array(m, n);
printf("the string are:\n");
for (k=0; k<m; ++k) {
printf("%s\n", p[k]);
}
return 0;
}
I'm not sure if I do this smart, but I usually allocate the pointer array and then allocate the whole memory chunk to the first item. Then I get continuous memory for the data. Like:
_array = (float**) malloc( n * sizeof ( float * ));
assert ( _array != NULL );
_array[0] = (float*) malloc( n * m * sizeof ( float ));
assert ( _array[0] != NULL );
for ( idx = 0; idx < n; idx++ )
_array[ idx ] = _array[ 0 ] + idx * m;
(float instead of int in my case. And please don't comment on the return of malloc casting, nor on the silly user of assert())
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)])