Fix %C format (c++98 standard) [skip ci]

Author: fruggiero

StrftimeParser/Strftime.cs

@@ -108,9 +108,12 @@ public static DateTime Parse(string input, string format, CultureInfo culture)
             // Year divided by 100
             if (elements.YearDividedBy100 != null)
             {
-                var yearDivided = Formatter.ParseYearDividedBy100(elements.YearDividedBy100);
-                if (year != null && !yearDivided.Equals(year / 100)) throw new FormatException("Incoherent year");
-                year = yearDivided * 100;
+                if (year == null) year = 1970;
+                else
+                {
+                    var yearDivided = Formatter.ParseYearDividedBy100(elements.YearDividedBy100);
+                    if (year != null && !yearDivided.Equals(year / 100)) throw new FormatException("Incoherent year");
+                }
             }
 
             // Day of the month

test/StrftimeParserTest/ParserTest.cs

@@ -155,12 +155,12 @@ public void ParseShortYyyyMmDd(string input, string format, int year, int month,
         }
 
         [Theory]
-        [InlineData("20", "%C", 2000)]
-        [InlineData("23", "%C", 2300)]
-        [InlineData("19", "%C", 1900)]
-        [InlineData("03", "%C", 300)]
-        [InlineData("20 2023", "%C %Y", 2000)]
-        [InlineData("19 1975", "%C %Y", 1900)]
+        [InlineData("20", "%C", 1970)]
+        [InlineData("23", "%C", 1970)]
+        [InlineData("19", "%C", 1970)]
+        [InlineData("03", "%C", 1970)]
+        [InlineData("20 2023", "%C %Y", 2023)]
+        [InlineData("19 1975", "%C %Y", 1975)]
         public void ParseYearDividedBy100(string input, string format, int expectedYear)
         {
             var res = Strftime.Parse(input, format, _culture);