C # Verification Code

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;namespaceVerification Code string procedure {classProgram {Static voidMain (string[] args) {            //define a set of strings            string[] s=New string[ +]            {"0","1","2","3","4","5","6","7","8","9",                "a","b","C","D","e","F","g","h","I","J","k","L","m","N","o","P","Q","R","s",             "T","u","v","W","x","y","Z",                "A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q",            "R","S","T","U","V","W","X","Y","Z"            }; stringA="";//defines a character variable with a value of NULLRandom ran =NewRandom ();  for(inti =0; I <4; i++ )            {                intSuijishu = ran. Next (0, +); A+ = S[suijishu];//Four randomly generated characters are linked to a string representing the verification code} Console.WriteLine ("Verification Code:"+a); stringb = A.toupper ();//background execution converts all the resulting strings to uppercaseConsole.Write ("Please enter the verification code:"); stringR =Console.ReadLine (); stringQ = R.toupper ();//converts a user-entered string all to uppercase            if(q = =b) {Console.WriteLine ("Verify Success! "); }            Else{Console.WriteLine ("input Error! ");        } console.readline (); }    }}

C # Verification code