Added exit.cpp

+#include <iostream>
+#include <string>
+using namespace std;
+
+int main(){
+    string str;
+    while(1){
+        cout << "If you want exit, Input \"exit\" : ";
+        cin >> str;
+        if(str == "exit"){
+            exit(100);
+        }
+    }
+    return 0;
+}
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