Create a BMI calculator that reads the user’s weight in pounds and height in inches (or, if you prefer, the user’s weight in kilograms and height in meters), then calculates and displays the user’s body mass index.

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As of 2013 there is also a new formula around:
BMI = 1.3 x weight(kg)/height(m)^2.5 = 5734 x weight(lb)/height(in)^2.5

cout << "you're morbidly obese!" << endl

There you go.