View Compilation Error

0_0_27908335_25753.cpp:2:9: error: 'complex' does not name a type
 typedef complex<double> cd;//复数类的定义
         ^
0_0_27908335_25753.cpp:5:1: error: 'cd' does not name a type
 cd a[maxl],b[maxl];//用于储存变换的中间结果
 ^
0_0_27908335_25753.cpp:6:10: error: variable or field 'fft' declared void
 void fft(cd* a,int n,int dft){//变换主要过程
          ^
0_0_27908335_25753.cpp:6:10: error: 'cd' was not declared in this scope
0_0_27908335_25753.cpp:6:14: error: 'a' was not declared in this scope
 void fft(cd* a,int n,int dft){//变换主要过程
              ^
0_0_27908335_25753.cpp:6:16: error: expected primary-expression before 'int'
 void fft(cd* a,int n,int dft){//变换主要过程
                ^
0_0_27908335_25753.cpp:6:22: error: expected primary-expression before 'int'
 void fft(cd* a,int n,int dft){//变换主要过程
                      ^