C#

• Underweight = <18.5
• Normal weight = 18.5-24.9
• Overweight = 25-29.9
• Obesity = >=30

if (bmi < 18.5)
{
    // underweight
}
else if (bmi < 25) // 18.5-24.9 (because we already checked <18.5 in the previous 'if'
{
    // normal weight
}
else if (bmi < 30) // 25-29.9
{
    // overweight
}
else // >= 30
{
    // obesity
}

string a = "hello";
string b = a;
b += " world";

string myBook = "";
foreach(string line in myDatabaseRows)
   {
   myBook += line;
   }

StringBuilder myBook = new StringBuilder();
foreach(string line in myDatabaseRows)
   {
   myBook.Append(line);
   }
string output = myBook.ToString();

StringBuilder myBook = new StringBuilder(1000000);