/in/foo.c: In function 'main':
/in/foo.c:5:5: error: unknown type name 'douoble'
     douoble a,r,theta,ans;
     ^~~~~~~
/in/foo.c:6:11: warning: format '%lf' expects argument of type 'double *', but argument 2 has type 'int *' [-Wformat=]
  scanf("%lf %lf",&a,&r);
           ^
/in/foo.c:6:15: warning: format '%lf' expects argument of type 'double *', but argument 3 has type 'int *' [-Wformat=]
  scanf("%lf %lf",&a,&r);
               ^
/in/foo.c:7:8: warning: implicit declaration of function 'acos' [-Wimplicit-function-declaration]
  theta=acos((2*a*a-r*r)/(2*r*r));
        ^~~~
/in/foo.c:7:8: warning: incompatible implicit declaration of built-in function 'acos'
/in/foo.c:7:8: note: include '<math.h>' or provide a declaration of 'acos'
/in/foo.c:8:20: warning: implicit declaration of function 'sin' [-Wimplicit-function-declaration]
  ans=r*r*0.5*theta-sin(theta)*r*r
                    ^~~
/in/foo.c:8:20: warning: incompatible implicit declaration of built-in function 'sin'
/in/foo.c:8:20: note: include '<math.h>' or provide a declaration of 'sin'
/in/foo.c:9:2: error: expected ';' before 'printf'
  printf("%0.6lf",ans);
  ^~~~~~
/in/foo.c:5:23: warning: variable 'ans' set but not used [-Wunused-but-set-variable]
     douoble a,r,theta,ans;
                       ^~~