Question

When allocating memory for the 2-dimensional array using malloc(),segmentation fault occurs when the input size(matrix N*N) is more than 5 (i.e., N>5).

The below code is working fine for inputs(N) less than 5.

Could you please help me out in figuring the problem?

#include<stdio.h>
#include <stdlib.h>

int main(){
    int n;
    int i,j;
    int **adj;
    //reading size of a N*N matrix
    scanf("%d",&n);

    //dynamically allocating memory for a 2-dimensional array
    adj=(int**)malloc(sizeof(int)*n);
    for(i=0;i<n;i++){
        adj[i]=(int*)malloc(sizeof(int)*n);
    }

    //taking input from the file        
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            scanf("%d",&adj[i][j]);
        }
    }

    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            printf("%d\t",adj[i][j]);
        }
        printf("\n");
    }
    return 0;
}

Answer 1

This is incorrect:

adj=(int**)malloc(sizeof(int)*n);

as you are allocating an array of int*, not int. Change to:

adj = malloc(sizeof(int*)*n); /* Cast unnecessary. */
/* or: adj = malloc(sizeof(*adj)*n); */

---

Recommend checking return value of scanf() to ensure an int was correctly read:

if (1 == scanf("%d", &n))
{
}

Useful read: Do I cast the result of malloc?