opencv(4.5.1) c:\users\appveyor\appdata\local\temp\1\pip-req-build-kh7iq4w7\opencv\modules\imgproc\src\resize.cpp:4051: error: (-215:assertion failed) !ssize.empty() in function 'cv::resize'

void main(){

int num;
cout <<"Enter Number "<<num;
}