There is a prompt in a program
What is the correct form of it?
Enter height of a triangle
Enter a height of a triangle
Enter the height of a triangle
Enter the height of the triangle
'Enter the height of the triangle'. Since it is a computer program, we are indeed specific about the specific triangle - so it is 'the' everywhere.
"Enter triangle height".
Since it is a computer program, we are not keen to be offensively over-verbose.