Verifying That a String Contains Only Letters in C#

Verifying that a string contains only letters in C#

Only letters:

Regex.IsMatch(input, @"^[a-zA-Z]+$");

Only letters and numbers:

Regex.IsMatch(input, @"^[a-zA-Z0-9]+$");

Only letters, numbers and underscore:

Regex.IsMatch(input, @"^[a-zA-Z0-9_]+$");

Verifying that a string contains only letters in console application in c#

Use char.IsLetter to check if all the characters in a string are Letter.

if (name.All(char.IsLetter))
{
    //All characters are letters
}

It is same as:

if (name.All(r => char.IsLetter(r)))

Check if a string contains only letters, digits and underscores

I love Linq for this kind of question:

bool validA = sname.All(c => Char.IsLetterOrDigit(c) || c.Equals('_'));

Verifying that a string contains only uppercase letters and numbers in C#

All() takes a predicate which can be a lambda expression. You can use this to check IsLetter && IsUpper separately from IsDigit.

input.All(c => (Char.IsLetter(c) && Char.IsUpper(c)) || Char.IsDigit(c))

Try it online

Alternatively, you could use a regular expression that matches zero or more uppercase characters or digits:

using System.Text.RegularExpressions;

Regex r = new Regex(@"^[A-Z0-9]*$");
r.IsMatch(input);

Try it online

Regex explanation:

^[A-Z0-9]*$
^               Start of string
 [A-Z0-9]       The uppercase letter characters or the digit characters
         *      Zero or more of the previous
          $     End of string

Check if string contains only one type of letter C#

Try this:

private bool ContainsOnlyOneLetter(string String)
    {
        if(String.Length == 0)
        {
            return true;
        }
        for(int i = 0; i < String.Length;i++)
        {
            if(String.Substring(i,1) != String.Substring(0,1))
            {
                return false;
            }
        }
        return true;
    }

And you can use the function like this:

bool containsOneLetter = ContainsOnlyOneLetter("...");

        if (containsOneLetter == true)
        {
            //Put code here when the letters are the same...
        }
        else
        {
            //Code when there are different letters..
        }

How to check if a String contains any letter from a to z?

Replace your for loop by this :

errorCounter = Regex.Matches(yourstring,@"[a-zA-Z]").Count;

Remember to use Regex class, you have to using System.Text.RegularExpressions; in your import

Check string contains only alphabets in C# and other allowed charaters are: ., whitespace, ,

Try this

var regex = new Regex(@"(?i)^[a-z.,\s]+$");
bool res =  regex.IsMatch(subject);

How to validate that a string contains only certain characters

You need else block.

public void setFirstName(string newFirstName)
{
    bool valid;
    valid = System.Text.RegularExpressions.Regex.IsMatch(newFirstName, "^[- a-zA-Z]*$");
    if (valid)
    {
        firstName = newFirstName;
    }
    else
    {
        firstName = " ";
    }
}

Update

Your regex seems also wrong it needs * for zero or more occurance instead of ?.
Correct regex => ^[- a-zA-Z]*$

Click here to see working fiddle => link

Check a string if it only contains letters from the alphabet and not numbers or other stuff in C#?

This should do the job :

bool result = input.All(Char.IsLetter);

and also a regex solution :

Regex.IsMatch(theString, @"^[\p{L}]+$");

The Char.IsLetter is the better solution since it counts as a letter any language alphabets. This regex will also count them but still it looks more compact with IsLetter

Verifying that a string contains only letters in C++

No numbers:

if(std::none_of(str.begin(), str.end(), [](unsigned char c){return std::isdigit(c);})) {
    // stuff
}

All letters:

if(std::all_of(str.begin(), str.end(), [](unsigned char c){return std::isalpha(c);})) {
    // stuff
}