Here is the optimized solution in Java. Copy or view it below.
Java
package Problems_On_Number_System;
import java.util.Scanner;
public class OctalToDecimal {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("enter the octal value:");
String s = sc.nextLine();
int decimal = 0;
int pow = 0;
for (int i = s.length() - 1; i >= 0; i--) {
int val = s.charAt(i) - '0';
decimal += (val * Math.pow(8, pow));
pow++;
}
System.out.println(decimal);
sc.close();
}
}