Write the function findFirst(). The function has two parameters: a const char * s1 pointing to the first character in a C-style string, and a const char * s2. Return a pointer to the first appearance of s2 appearing inside s1 and nullptr (0) if s2 does not appear inside s. Here is the supporting file and please keep in mind we are working with c++ pointers and C-style strings/**CS 150 C-StringsFollow the instructions on your handout to complete the requested function. You may not use ANY library functions or include any headers, except for for size_t.*/#include // size_t for sizes and indexes WRITE YOUR FUNCTION BELOW THIS LINE function goes in here WRITE YOUR FUNCTION ABOVE THIS LINE These are OK after the function#include #include using namespace std;void CHECK(const char*, const char *, const string&);void studentTests(){cout << "Student testing. Add code in this function." << endl;cout << "" << endl;CHECK("Aardvark", "dv", "dvark");CHECK("Aardvark", "k", "k");CHECK("Aardvark", "rdv", "rdvark");CHECK("Aardvark", "arki", "nullptr");cout << endl;cout << "--done--" << endl;}int main(){studentTests();}#include void CHECK(const char * s1, const char * s2, const string& expected){string msg = "findFirst(\"" + string(s1) + "\", \"" + string(s2) + "\")";char d1[1024], d2[1024];strcpy(d1, s1);strcpy(d2, s2);auto p = findFirst(d1, d2);string actual = (p ? string(p) : "nullptr");if (expected == actual)cout << " + " + msg + "->OK" << endl;elsecout << " X " + msg + " expected<\"" + expected + "\">, found <\"" + actual + "\">" << endl;}