c - How to dynamically allocate memory in 2D array and store values? -

i trying allocate memory in 2d array dynamically, don't know wrong.

error
let input is

2 2 1 2 3 4 5 6 7 8 9 ........ 

then program crashes

#include<stdio.h> #include<stdlib.h>  int main() {     int n,m;     int i,j;     scanf("%d %d",&n,&n);      int **a = (int **)malloc(n*sizeof(int *));      for(i=0;i<n;i++)     {         a[i] = (int *)malloc(m*sizeof(int));     }      for(i=0;i<n;i++)     {         for(j=0;j<m;j++)         {             scanf("%d",&a[i][j]);         }     }      for(i=0;i<n;i++)     {         for(j=0;j<m;j++)         {             printf("%d",a[i][j]);         }     }      return 0; } 

as said problem in scanning n , m variables.

change

scanf("%d %d",&n,&n); 

to

scanf("%d",&n); scanf("%d",&m); 

and fine.

problem reading n twice while didnt read m used uninitialized.

non-static variables (local variables) indeterminate. reading them prior assigning value results in undefined behavior.

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you should free allocated memory

for(i=0;i<n;i++) {     free(a[i]); } free(a); 

and dont cast malloc()'s return value becouse

• its reduntand
• adding cast may mask failure include header stdlib.h, in prototype malloc found
• if type of pointer changed, 1 must fix code lines malloc() called , cast

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next time if cannot find bug, try use debugger , happening, can see variable values, see m uninitialized , didnt change after scanf().