(Homework) a single integer argument between 1 to 20 ( the program should test this range and give a response accordingly while out of range

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C++

Write a C++ program which takes a single integer argument between 1 to 20 ( the program should test this range and give a response accordingly while out of range, otherwise displays a "pyramid" of a height of input value made up of of "A" characters on the screen. The program should not be function based it should b a single program.