Replace the string array value

[julioferret]

My string structure is below. I want to insert the new value in fourth position instead of old one.How can i insert it.\[code\]Array structure :arr_val[0]="100";arr_val[1]="300";arr_val[2]="150";arr_val[3]="360"; //I want to replace this value and insert 200 in this arrayarr_val[4]="100";arr_val[5]="300";\[/code\]I can't sure the fourth value may be changed.