/in/foo.c: In function 'main':
/in/foo.c:13:8: warning: implicit declaration of function 'PD' [-Wimplicit-function-declaration]
  count=PD(x,n);
        ^~
/in/foo.c: In function 'PD':
/in/foo.c:22:18: error: 'm' undeclared (first use in this function)
    if(x[i]+x[j]==m)
                  ^
/in/foo.c:22:18: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:23:5: error: 'count' undeclared (first use in this function)
     count+=count;
     ^~~~~
/in/foo.c:25:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^