How to pass a 2D array as a parameter in C? - c

Question

The section of function is never entered in the following code
please help me out!
#include<stdio.h>
int findMax(int *a[], int m, int n)//this function is not entering
{
int i,j,k=0;
for(i=0;i<m;i++)
for(j=0;j<n;j++)
if(k<a[i][j])
k=a[i][j];
printf("hi");//this hi is also not printing
//this hi is just for testing
return k;
}
//This function correct it if possible
int main()
{
int m,n,a[50][50],i,j,k=0;
printf("Enter the number of rows in the matrix\n");
scanf("%d",&m);
printf("Enter the number of columns in the matrix\n");
scanf("%d",&n);
printf("Enter the elements in the matrix\n");
for(i=0;i<m;i++)
for(j=0;j<n;j++)
{
scanf("%d",&a[i][j]);
}
printf("The matrix is");
for(i=0;i<m;i++)
{
printf("\n");
for(j=0;j<n;j++)
printf("%d ",a[i][j]);
}
k=findMax((int **)a,m,n);//statements after this is never running but no
//compilation errors
printf("\nThe maximum element in the matrix is %d",k);
return 0;
}
please help me out!!
Thanks to you in advance!!

Answer 1

what you are doing here: int findMax(int *a[], int m, int n) is trying to point at int 50 times, but you want to point at a variabile type int 50 times. therefor you want to decleare the pointer before you decleare the array.
use therefor:
int findMax(int (*a)[], int m, int n)
this should work now without the casting
just turn it into:
k=findmax(a,m,n);
here is a simple tutorial on the subject.

Answer 2

int findMax(int *a[], int m, int n)
int *a[] is an array of pointers to int, you want a pointer to an array of 50 int's:
int findMax(int (*a)[50], int m, int n)
or
int findMax(int a[][50], int m, int n)
You don't need the cast, call it using:
k = findMax(a, m, n);
Or you can use a flat array, an example:
#include <stdio.h>
void foo(int *arr, int rows, int cols)
{
int i, j;
for (i = 0; i < rows; i++) {
for (j = 0; j < cols; j++)
printf("%d ", arr[i * cols + j]);
printf("\n");
}
}
#define ROWS 3
#define COLS 3
int main(void)
{
int arr[ROWS * COLS];
int i, j;
for (i = 0; i < ROWS; i++) {
for (j = 0; j < COLS; j++)
arr[i * COLS + j] = i * COLS + j;
}
foo(arr, ROWS, COLS);
return 0;
}
If you dont know the sizes of the 2d array beforehand you can use malloc:
#include <stdio.h>
#include <stdlib.h>
void foo(int *arr, int rows, int cols)
{
int i, j;
for (i = 0; i < rows; i++) {
for (j = 0; j < cols; j++)
printf("%d ", arr[i * cols + j]);
printf("\n");
}
}
int main(void)
{
int i, j, rows, cols;
int *arr;
printf("Num of rows:");
scanf("%d", &rows);
printf("Num of cols:");
scanf("%d", &cols);
arr = malloc(rows * cols);
if (arr == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
for (i = 0; i < rows; i++) {
for (j = 0; j < cols; j++)
arr[i * cols + j] = i * cols + j;
}
foo(arr, rows, cols);
free(arr);
return 0;
}

Answer 3

#include <stdio.h>
#include <limits.h>
#define MATRIX_SIZE 50
int findMax(int a[MATRIX_SIZE][MATRIX_SIZE], int m, int n){
//Valid any of the following is
//int a[MATRIX_SIZE][MATRIX_SIZE]
//int a[][MATRIX_SIZE]
//int (*a)[MATRIX_SIZE]
int i, j, k=INT_MIN;
for(i=0;i<m;i++)
for(j=0;j<n;j++)
if(k<a[i][j])
k=a[i][j];
return k;
}
int main(void){
int m, n, a[MATRIX_SIZE][MATRIX_SIZE], i, j, k=0;
printf("Enter the number of rows(<=50) in the matrix\n");
scanf("%d",&m);
printf("Enter the number of columns(<=50) in the matrix\n");
scanf("%d",&n);
if(m < 1 || n < 1 || m > 50 || n > 50){
printf("invalid input!\n");
return -1;
}
printf("Enter the elements in the matrix\n");
for(i=0;i<m;i++)
for(j=0;j<n;j++)
scanf("%d",&a[i][j]);
printf("The matrix is");
for(i=0;i<m;i++){
printf("\n");
for(j=0;j<n;j++)
printf("%d ",a[i][j]);
}
k=findMax(a, m, n);
printf("\nThe maximum element in the matrix is %d\n", k);
return 0;
}