fix handling of rounding to 12 inches in FeetInches

UnitsNet/CustomCode/Quantities/Length.extra.cs

@@ -161,7 +161,17 @@ public string ToString(IFormatProvider? cultureInfo)
 
             // Note that it isn't customary to use fractions - one wouldn't say "I am 5 feet and 4.5 inches".
             // So inches are rounded when converting from base units to feet/inches.
-            return string.Format(cultureInfo, "{0:n0} {1} {2:n0} {3}", Feet, footUnit, Math.Round(Inches), inchUnit);
+            // When we do this we check if we rounded inches to 12(InchesInOneFoot).
+            // If it does feet/inches are fixed something like 4 ft 0 in is displayed instead of 3ft 12 in for things very close to 4 e.g. 3.9999 ft 
+            var feet = Feet;
+            var inches = Math.Round(Inches);
+            if(inches == InchesInOneFoot)
+            {
+                feet++;
+                inches = 0;
+            }
+
+            return string.Format(cultureInfo, "{0:n0} {1} {2:n0} {3}", feet, footUnit, inches, inchUnit);
         }
 
         /// <summary>
@@ -190,6 +200,7 @@ public string ToArchitecturalString(int fractionDenominator)
                 throw new ArgumentOutOfRangeException(nameof(fractionDenominator), "Denominator for fractional inch must be greater than zero.");
             }
 
+            var feet = Feet;
             var inchTrunc = (int)Math.Truncate(Inches);
             var numerator = (int)Math.Round((Inches - inchTrunc) * fractionDenominator);
 
@@ -199,6 +210,12 @@ public string ToArchitecturalString(int fractionDenominator)
                 numerator = 0;
             }
 
+            if (inchTrunc == InchesInOneFoot)
+            {
+                feet++;
+                inchTrunc = 0;
+            }
+
             var inchPart = new System.Text.StringBuilder();
 
             if (inchTrunc != 0 || numerator == 0)
@@ -238,7 +255,7 @@ int GreatestCommonDivisor(int a, int b)
                 return inchPart.ToString();
             }
 
-            return $"{Feet}' - {inchPart}";
+            return $"{feet}' - {inchPart}";
         }
     }
 }