/in/foo.c: In function 'main':
/in/foo.c:9:18: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
  else if(x<25){y=sqrt(5*x+10);}
                  ^~~~
/in/foo.c:9:18: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:9:18: note: include '<math.h>' or provide a declaration of 'sqrt'