/in/foo.c: In function 'main':
/in/foo.c:4:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d",&n);
  ^~~~~
/in/foo.c:4:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:4:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:5:4: warning: implicit declaration of function 'count' [-Wimplicit-function-declaration]
  s=count(2,n);
    ^~~~~
/in/foo.c:6:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%d\n",s);
  ^~~~~~
/in/foo.c:6:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:6:2: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c: In function 'prime':
/in/foo.c:15:13: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
  for(s=2;s<=sqrt(x);s++)
             ^~~~
/in/foo.c:15:13: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:15:13: note: include '<math.h>' or provide a declaration of 'sqrt'
/in/foo.c: In function 'count':
/in/foo.c:24:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(m=a;m<=b;m++)
  ^~~
/in/foo.c:27:3: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
   return s;
   ^~~~~~