c# - Replace the string array value -

my string structure below. want insert new value in fourth position instead of old one.how can insert it.

array structure :   arr_val[0]="100"; arr_val[1]="300"; arr_val[2]="150"; arr_val[3]="360"; //i want replace value , insert 200 in array arr_val[4]="100"; arr_val[5]="300"; 

i can't sure fourth value may changed.

like did when initialized arrayvariable can set new value:

arr_val[3] = "200";