(C# Language) Practice Exercise on String Manipulation

Write a program to count the number of 'a' in this string

Open the program.cs file of the solution explorer and start by creating the given string.

//-- program 1 --//

string s = "aubcd123paqeaw";

int count = 0;

foreach (Char k in s)
{
  if ('a' == k)
  {
    count++;
  }
}

// prints 3 
Console.WriteLine($"Number of a = {count}");

Create an int count = 0 so that we can use it to store the number of 'a'.

A string is a sequence of Char. So we can set a for-each loop - foreach char k in s. Next, an if condition checks if the char is an 'a'. If so, the counter is incremented. Finally, the contents of the counter are printed!

Video Explanation (see it happen!)

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Write a program to extract the numeric part into a string variable and display it

Open the program.cs file of the solution explorer and again start by creating the given string.

//-- program 2 --//

string s = "aubcd123paqeaw";

using System.Text;

StringBuilder sb = new();

foreach(Char k in s)
{
  if(Char.IsDigit(k))
  {
    sb.Append(k);
  }
}

Console.WriteLine(sb.ToString());

We have to store the numeric part in a separate string. So we start with a StringBuilder.

A for-each loop checks each char of the string if it is a numeral. It uses the static Char.IsDigit function for this check. Alternatively, we could have made a check of ASCII values k >= '0' AND k <='9'. If the char is a numeric, then it is appended to the string builder.

Finally, the string builder is converted to a string and displayed.

Replace all vowels by underscore

Open the program.cs file of the solution explorer and again start by creating the given string.

//-- program 3 --//

string s = "aubcd123paqeaw";

StringBuilder sb2 = new();

foreach (char k in s)
{
  switch (k)
  {
    case 'a': case 'A':
    case 'e': case 'E':
    case 'i': case 'I':
    case 'o': case 'O':
    case 'u': case 'U':
      {
        sb2.Append('_');
      }
      break;

    default:
      {
        sb2.Append(k);
      }
      break;
  }
}

Console.WriteLine(sb2.ToString());

We start with a string builder.

A foreach loop is created to loop through the characters of the given string.

A switch statement appends an underscore to the string builder if the char is a vowel. Otherwise the default case appends the character to the string builder.

Finally, the string builder is converted to a string and displayed.