foo.c: In function ‘main’:
foo.c:18:27: warning: implicit declaration of function ‘pow’ [-Wimplicit-function-declaration]
   18 |                 b+=change*pow(10,count-number);
      |                           ^~~
foo.c:2:1: note: include ‘<math.h>’ or provide a declaration of ‘pow’
    1 | #include <stdio.h>
  +++ |+#include <math.h>
    2 | 
foo.c:18:27: warning: incompatible implicit declaration of built-in function ‘pow’ [-Wbuiltin-declaration-mismatch]
   18 |                 b+=change*pow(10,count-number);
      |                           ^~~
foo.c:18:27: note: include ‘<math.h>’ or provide a declaration of ‘pow’