/in/foo.c: In function 'main':
/in/foo.c:53:3: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
   scanf("%d", &n);
   ^~~~~
/in/foo.c:53:3: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:53:3: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:60:7: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
       printf("%4d ",a[i][j]);
       ^~~~~~
/in/foo.c:60:7: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:60:7: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:62:5: warning: incompatible implicit declaration of built-in function 'printf'
     printf("\n");
     ^~~~~~
/in/foo.c:62:5: note: include '<stdio.h>' or provide a declaration of 'printf'