/in/foo.c: In function 'main':
/in/foo.c:11:24: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
   for (j = 2; j <=(int)sqrt((double)i); j++) {
                        ^~~~
/in/foo.c:11:24: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:11:24: note: include '<math.h>' or provide a declaration of 'sqrt'