(Longest common prefix) Write the prefix function using the following function header to return the longest common prefix between two strings:
string prefix (const string& s1, const string& s2)
Write a test program that prompts the user to enter two strings and displays their longest common prefix. Sample runs of the program are the same as in Programming Exercise.
Programming Exercise (Longest common prefix) Write a program that prompts the user to enter two strings
and displays the largest common prefix of the two strings. Here are sample runs:


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