Question

write a qbasic program to find out whether it is a triangle or not​

Answer 1

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Qbasic program to input sides of a triangle and check for isosceles triangle. Input three sides of a triangle whether the given triangle is a isosceles.

or

You have two choices, use a numbered menu 1,2,3, for Circle square triangle or use text input for letters. The number is easier because Qbasic can parse numbers for legal answers quickly. You would have to parse for upper and lower case and legal or non-legal entries, truncate if more than one character, so its more difficult.