Write a function ReplaceSubString that takes three strings as parameters: string1, string2, and string3 and modifies one or more substrings of string1.The function should search string1 for all occurrences of string2. When it finds an occurrence of string2, it should replace it with string3 and save the result in a new string string4.For example, suppose the three strings have the following values:String1: "the dog jumped over the fence"String2: "the"String3: "that"The new string object will have the value "that dog jumped over that fence".Write a main program to test your function. Your main program should:- read three strings from the user: string1, string2, and string3 (You may use the string values provided above)- call the function ReplaceSubString to modify string1- display the new string. Note:- You should make sure string2 and string3 are not the same.- You may use string member functions such as find, replace…