递归检查字符串中的所有字母是否都是大写

Question

I have to check if all the letters are capital letters in recursion, and i dont know why this isnt working:

public static bool IsCapital(string str)
    {
        if (str.Length == 1)
            return int.Parse(str[0].ToString()) > 65 && int.Parse(str[0].ToString()) < 90;
        return IsCapital(str.Substring(1)) && int.Parse(str[0].ToString()) > 65 && int.Parse(str[0].ToString()) < 90;
    }

It crashes and says: "Unhandled exception: System.FormatException: Input string was not in a correct format."

Console.WriteLine(IsCapital("abc"));

thanks.

Answer 1

You're attempting to parse a char as an int , instead of casting it to an int .

What you're doing is taking a letter, such as A , and parsing that as an int. A isn't a number in any way, and therefore the parse fails.

What you'll want to do is explicitly cast the char as an int to get the ASCII value you're looking for:

if (str.Length == 1)
{
    return ((int)str[0]) > 65 
        && ((int)str[0]) < 90;
}
return IsCapital(str.Substring(1)) 
    && ((int)str[0]) > 65 
    && ((int)str[0]) < 90;

Answer 2

I assume what you're trying to do with int.Parse(str[0].ToString()) is to get the ASCII value.

What you need to use instead is this (int)str[0]

A parse will try to translate the string into a number, so a string that has a value of '412' will get parsed into an int of value 412.

Answer 3

I have to check if all the letters are capital letters in recursion

public static bool IsCapital(string str)
{
    if (String.IsNullOrEmpty(str)) return false;
    if (str.Length == 1 &&  char.IsUpper(str[0])) return true;
    return char.IsUpper(str[0]) ? IsCapital(str.Substring(1)) :false;
}

Answer 4

To solely address the exception, just don't parse strings. You can directly compare a char to any ushort value.

In other words, this is a valid check (without string parsing)

str[0] > 65

AsciiTable.com should show you why the checks you have will fail on the edges.

Also consider...

• Characters that aren't letters.
• IsCapital(null)

Finally, something that might make this easier (assuming non-letters get bypassed) is to create a method along the lines of bool IsNotLowerCase(char c) .

Note -- these are all assuming ASCII, as evident by my link.

If you must support full Unicode, hopefully you can use the methods of char .

Answer 5

I thinks, that number comparison will not work.

First it will return false for string like this "ABC123" even if all letters are capitals. And second there are many national characters that does not fall into range 65..90 even if they are capitals. You should (if you can) use some Char method http://msdn.microsoft.com/en-us/library/d1x97616.aspx

Answer 6

While there are many ways to skin this cat, I prefer to wrap such code into reusable extension methods that make it trivial to do going forward. When using extension methods, you can also avoid RegEx as it is slower than a direct character check. I like using the extensions in the Extensions.cs NuGet package. It makes this check as simple as:

1. Add the [https://www.nuget.org/packages/Extensions.cs][1] package to your project.
2. Add " using Extensions; " to the top of your code.
3. "smith".IsUpper() will return False whereas "SMITH".IsUpper() will return True. 4. Every other check in the rest of the code is simply MyString.IsUpper() .

Your example code would become as simple as:

using Extensions;

//Console.WriteLine(IsCapital("abc"));
Console.WriteLine("abc".IsUpper());

Answer 7

public static bool IsCapital(string str)
{
 return !Regex.IsMatch(str, "[a..z]");
}