How to pass variables in C # To SQL

Newbie questions how to pass variables in C # To SQL, such as SqlCommand myCommand = new SqlCommand ("select zkzh, school, name, n1, fzf from yw01 where substring (zkzh, 5, 3) = '001' "I want to replace '001' with a variable fkd. What method should I use? Do I add any characters before the variable?

 

1. string fzf
= "001"; SqlCommand myCommand
= New SqlCommand ("select zkzh, school, name, n1, fzf
From yw01 where substring (zkzh, 5, 3) = @ fzf "; cmd. Parameters. Add (" @ fzf ", fzf );

 

2.

For example: String str = "select zkzh, school, name, n1, fzf from yw01 where aaa = '" + aaa + "'"; // String type variable String str = "select zkzh, school, name, n1, fzf from yw01 where aaa =" + aaa; // int Type Variable

If you use a stored procedure, you can also build parameter transfer, such:
SqlParameter [] paras = {new SqlParameter ("@ RolesName", SqlDbType. varChar, 50), new SqlParameter ("@ RolesDescription", SqlDbType. varChar, 100), new SqlParameter ("@ CreateDate", SqlDbType. dateTime, 8 )};
Paras [0]. Value = roles. RolesName;
Paras [1]. Value = roles. RolesDescription;
Paras [2]. Value = roles. CreateDate;