/in/foo.c: In function 'main':
/in/foo.c:6:20: warning: implicit declaration of function 'malloc' [-Wimplicit-function-declaration]
     int *p=(float*)malloc(4*n);
                    ^~~~~~
/in/foo.c:6:20: warning: incompatible implicit declaration of built-in function 'malloc'
/in/foo.c:6:20: note: include '<stdlib.h>' or provide a declaration of 'malloc'
/in/foo.c:6:12: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
     int *p=(float*)malloc(4*n);
            ^