/in/foo.c: In function 'main':
/in/foo.c:9:12: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
  a=(int **)malloc(nn*sizeof(int *));
            ^~~~~~
/in/foo.c:9:12: warning: incompatible implicit declaration of built-in function 'malloc'
/in/foo.c:9:12: note: include '<stdlib.h>' or provide a declaration of 'malloc'
/in/foo.c:12:14: warning: unused variable 'count' [-Wunused-variable]
  int flag=1, count=1;
              ^~~~~
/in/foo.c:12:6: warning: unused variable 'flag' [-Wunused-variable]
  int flag=1, count=1;
      ^~~~
/in/foo.c:6:13: warning: unused variable 'k' [-Wunused-variable]
  int n, nn, k=1, i=0, j=0;
             ^
/in/foo.c:6:6: warning: unused variable 'n' [-Wunused-variable]
  int n, nn, k=1, i=0, j=0;
      ^
/in/foo.c: In function 'Matrix':
/in/foo.c:29:3: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   if(flag=0)
   ^~