/in/foo.c: In function 'main':
/in/foo.c:24:24: warning: implicit declaration of function 'pow' [-Wimplicit-function-declaration]
             ans+=(a[j]*pow(i,j));
                        ^~~
/in/foo.c:24:24: warning: incompatible implicit declaration of built-in function 'pow'
/in/foo.c:24:24: note: include '<math.h>' or provide a declaration of 'pow'