As you spelled "string" with a lower case 's', I'll assume you're writing in
C++.
You need to research the member functions available in the C++ string class.
particularly the various overloads of the find() function and the replace()
function..
If my assumption above is incorrect, please tell us which language and class
library you are using.

ksrajalakshmi@gmail.com, the perspiring chiseler and thick-skulled brown
rod who likes vulgar 69ers with caribous, and whose partner is a
flesh-peddler with a slushy bunny tuft, wrote in
<1139643024.132357.104660@g47g2000cwa.googlegroups.com>:  

From the *HELP* *TEXT*...

     Visual Basic
' This example demonstrates the String.Contains() method
Imports System

Class Sample
  Public Shared Sub Main()
     Dim s1 As String = "The quick brown fox jumps over the lazy dog"
     Dim s2 As String = "fox"
     Dim b As Boolean
     b = s1.Contains(s2)
     Console.WriteLine("Is the string, s2, in the string, s1?: {0}", b)
  End Sub 'Main
End Class 'Sample
'
'This example produces the following results:
'
'Is the string, s2, in the string, s1?: True
'

     C#
// This example demonstrates the String.Contains() method
using System;

class Sample
{
   public static void Main()
   {
   string s1 = "The quick brown fox jumps over the lazy dog";
   string s2 = "fox";
   bool b;
   b = s1.Contains(s2);
   Console.WriteLine("Is the string, s2, in the string, s1?: {0}", b);
   

/*
This example produces the following results:

Is the string, s2, in the string, s1?: True
*/

     C++
// This example demonstrates the String.Contains() method
using namespace System;
int main()
{
  String^ s1 = "The quick brown fox jumps over the lazy dog";
  String^ s2 = "fox";
  bool b;
  b = s1->Contains( s2 );
  Console::WriteLine( "Is the string, s2, in the string, s1?: {0}", b );

/*
This example produces the following results:

Is the string, s2, in the string, s1?: True
*/

     Visual Basic
' Sample for String.IndexOf(Char, Int32)
Imports System

Class Sample
  Public Shared Sub Main()

     Dim br1 As String =
"0----+----1----+----2----+----3----+----4----+----5----+----6----+-"
     Dim br2 As String =
"0123456789012345678901234567890123456789012345678901234567890123456"
     Dim str As String = "Now is the time for all good men to come to the
aid of their party."
     Dim start As Integer
     Dim at As Integer

     Console.WriteLine()
     Console.WriteLine("All occurrences of 't' from position 0 to {0}.",
str.Length - 1)
     Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2,
str)
     Console.Write("The letter 't' occurs at position(s): ")

     at = 0
     start = 0
     While start < str.Length AndAlso at > - 1
        at = str.IndexOf("t"c, start)
        If at = - 1 Then
           Exit While
        End If
        Console.Write("{0} ", at)
        start = at + 1
     End While
     Console.WriteLine()
  End Sub 'Main
End Class 'Sample
'
'This example produces the following results:
'
'All occurrences of 't' from position 0 to 66.
'0----+----1----+----2----+----3----+----4----+----5----+----6----+-
'0123456789012345678901234567890123456789012345678901234567890123456
'Now is the time for all good men to come to the aid of their party.
'
'The letter 't' occurs at position(s): 7 11 33 41 44 55 64
'
'

     C#
// Sample for String.IndexOf(Char, Int32)
using System;

class Sample {
   public static void Main() {

   string br1 =
"0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
   string br2 =
"0123456789012345678901234567890123456789012345678901234567890123456";
   string str = "Now is the time for all good men to come to the aid of
their party.";
   int start;
   int at;

   Console.WriteLine();
   Console.WriteLine("All occurrences of 't' from position 0 to {0}.",
str.Length-1);
   Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2,
str);
   Console.Write("The letter 't' occurs at position(s): ");

   at = 0;
   start = 0;
   while((start < str.Length) && (at > -1))
       {
       at = str.IndexOf('t', start);
       if (at == -1) break;
       Console.Write("{0} ", at);
       start = at+1;
       
   Console.WriteLine();
   

/*
This example produces the following results:

All occurrences of 't' from position 0 to 66.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The letter 't' occurs at position(s): 7 11 33 41 44 55 64

*/

     C++
// Sample for String::IndexOf(Char, Int32)
using namespace System;
int main()
{
  String^ br1 =
"0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
  String^ br2 =
"0123456789012345678901234567890123456789012345678901234567890123456";
  String^ str = "Now is the time for all good men to come to the aid of
their party.";
  int start;
  int at;
  Console::WriteLine();
  Console::WriteLine( "All occurrences of 't' from position 0 to {0}.",
str->Length - 1 );
  Console::WriteLine( "{1}{0}{2}{0}{3}{0}", Environment::NewLine, br1, br2,
str );
  Console::Write( "The letter 't' occurs at position(s): " );
  at = 0;
  start = 0;
  while ( (start < str->Length) && (at > -1) )
  {
     at = str->IndexOf( 't', start );
     if ( at == -1 )
           break;}

     Console::Write( "{0} ", at );
     start = at + 1;
 

  Console::WriteLine();
}

/*
This example produces the following results:

All occurrences of 't' from position 0 to 66.
0----+----1----+----2----+----3----+----4----+----5----+----6----+-
0123456789012345678901234567890123456789012345678901234567890123456
Now is the time for all good men to come to the aid of their party.

The letter 't' occurs at position(s): 7 11 33 41 44 55 64

*/