View Compilation Error

0_0_20965625_27399.cpp: In function 'int dcmp(double, double)':
0_0_20965625_27399.cpp:5:16: error: 'abs' was not declared in this scope
     if (abs(a-b)<EPS) return 0;
                ^
0_0_20965625_27399.cpp: At global scope:
0_0_20965625_27399.cpp:23:1: error: 'priority_queue' does not name a type
 priority_queue<Dat>que;
 ^
0_0_20965625_27399.cpp: In function 'int main()':
0_0_20965625_27399.cpp:30:26: error: 'scanf' was not declared in this scope
     while (~scanf("%d",&n)){
                          ^
0_0_20965625_27399.cpp:31:17: error: 'que' was not declared in this scope
         while (!que.empty()) que.pop();
                 ^
0_0_20965625_27399.cpp:36:23: error: 'sort' was not declared in this scope
         sort(a,a+n,cmp);
                       ^
0_0_20965625_27399.cpp:40:13: error: 'que' was not declared in this scope
             que.push(a[i]);
             ^
0_0_20965625_27399.cpp:61:29: error: 'printf' was not declared in this scope
         printf("%0.2f\n",sum);
                             ^