View Compilation Error

0_0_20806090_15428.cpp: In function 'int main()':
0_0_20806090_15428.cpp:10:24: error: no matching function for call to 'a::a(int&)'
     arr a[]=new arr(num);
                        ^
0_0_20806090_15428.cpp:10:24: note: candidates are:
0_0_20806090_15428.cpp:3:16: note: a::a()
 typedef struct a{
                ^
0_0_20806090_15428.cpp:3:16: note:   candidate expects 0 arguments, 1 provided
0_0_20806090_15428.cpp:3:16: note: constexpr a::a(const a&)
0_0_20806090_15428.cpp:3:16: note:   no known conversion for argument 1 from 'int' to 'const a&'
0_0_20806090_15428.cpp:3:16: note: constexpr a::a(a&&)
0_0_20806090_15428.cpp:3:16: note:   no known conversion for argument 1 from 'int' to 'a&&'