Question10.java

import java.util.*;
public class Question10 {
	static int val(char c) {
		if (c >= '0' && c <= '9')
			return (int) c - '0';
		else
			return (int) c - 'A' + 10;
	}

	static int toDeci(String str, int base) {

		int len = str.length();
		int power = 1;
		int num = 0;
		for (int i = len - 1; i >= 0; i--) {

			if (val(str.charAt(i)) >= base) {
				System.out.printf("Invalid Number");
				return -1;
			}
			num += val(str.charAt(i)) * power;
			power = power * base;
		}
		return num;
	}
	static char reVal(int num) {
		if (num >= 0 && num <= 9)
			return (char) (num + '0');
		else
			return (char) (num - 10 + 'A');
	}

	static String fromDeci(int base, int inputNum) {
		String res = "";

		while (inputNum > 0) {

			res += reVal(inputNum % base);

			inputNum /= base;
		}

		res = reverse(res);

		return res;
	}

	static void convertBase(String s, int a, int b) {

		int num = toDeci(s, a);
		String ans = fromDeci(b, num);
		System.out.print(ans);
	}

	static String reverse(String input) {
		char[] a = input.toCharArray();
		int l, r = a.length - 1;
		for (l = 0; l < r; l++, r--) {
			char temp = a[l];
			a[l] = a[r];
			a[r] = temp;
		}
		return String.valueOf(a);
	}

	// Driver Code
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.print("Enter the number: ");
		String s = sc.next();

		System.out.print("Enter base1: ");
		int a = sc.nextInt();
		System.out.print("Enter base2: ");
		int b = sc.nextInt();
		convertBase(s, a, b);

		sc.close();

	}

}
/*Satyam Sekhar Barik
 * Regd-no : 2141002032
 * sec : CSE-U
 * */