() is generally used for the parameter list after the function, that is, the parameters of the function are in parentheses. For calculation formulas, parentheses have the highest priority.

Is to take the data value of row 3 and column 4 of matrix A.

{} In C#, braces still play several different roles: representing hierarchical relationships (such as braces used when defining namespaces and classes), representing compound statements (such as braces in if and for), and representing array elements. The part enclosed by a pair of curly braces is a level, and the variables defined at this level can only be used inside the curly braces, not outside the curly braces.