 # rootulp's solution

## to Octal in the Java Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Convert an octal number, represented as a string (e.g. '1735263'), to its decimal equivalent using first principles (i.e. no, you may not use built-in or external libraries to accomplish the conversion).

Implement octal to decimal conversion. Given an octal input string, your program should produce a decimal output.

## Note

• Implement the conversion yourself. Do not use something else to perform the conversion for you.
• Treat invalid input as octal 0.

Decimal is a base-10 system.

A number 233 in base 10 notation can be understood as a linear combination of powers of 10:

• The rightmost digit gets multiplied by 10^0 = 1
• The next number gets multiplied by 10^1 = 10
• ...
• The nth number gets multiplied by 10^(n-1).
• All these values are summed.

So:

``````   233 # decimal
= 2*10^2 + 3*10^1 + 3*10^0
= 2*100  + 3*10   + 3*1
``````

Octal is similar, but uses powers of 8 rather than powers of 10.

So:

``````   233 # octal
= 2*8^2 + 3*8^1 + 3*8^0
= 2*64  + 3*8   + 3*1
= 128   + 24    + 3
= 155
``````

# Running the tests

You can run all the tests for an exercise by entering

``````\$ gradle test
``````

## Source

All of Computer Science http://www.wolframalpha.com/input/?i=base+8

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### OctalTest.java

``````import org.junit.Test;
import org.junit.Ignore;

import static org.junit.Assert.assertEquals;

public class OctalTest {

@Test
public void testCovertDecimalOneToOctal() {
Octal octal = new Octal("1");
assertEquals(1, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testCovertDecimalTenToOctal() {
Octal octal = new Octal("10");
assertEquals(8, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testCovertDecimalSeventeenToOctal() {
Octal octal = new Octal("17");
assertEquals(15, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testCovertElevenToOctal() {
Octal octal = new Octal("11");
assertEquals(9, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testCovertDecimalElevenWithZeroToOctal() {
Octal octal = new Octal("011");
assertEquals(9, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testThreeDigitDecimalToOctal() {
Octal octal = new Octal("130");
assertEquals(88, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testSmallFourDigitDecimalToOctal() {
Octal octal = new Octal("2047");
assertEquals(1063, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testLargeFourDigitDecimalToOctal() {
Octal octal = new Octal("7777");
assertEquals(4095, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testSevenDigitDecimalToOctal() {
Octal octal = new Octal("1234567");
assertEquals(342391, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testInvalidStringFirst() {
Octal octal = new Octal("carrot");
assertEquals(0, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testInvalidStringSecond() {
Octal octal = new Octal("abc1z");
assertEquals(0, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testInvalidDecimalEight() {
Octal octal = new Octal("8");
assertEquals(0, octal.getDecimal());
}

@Ignore("Remove to run test")
@Test
public void testInvalidNumberNine() {
Octal octal = new Octal("9");
assertEquals(0, octal.getDecimal());
}

}``````
``````import java.lang.Math;

public final class Octal {

private String input;
private int decimal;

public Octal(String input) {
this.input = input;
decimal = calculateDecimal();
}

public int getDecimal() {
return decimal;
}

private int calculateDecimal() {
int decimal = 0;
if (!input.matches("[0-7]+")) { return decimal; }

for (int i = 0; i < input.length(); i++) {
int curr = Character.getNumericValue(input.charAt(i));
int mult =  (int) Math.pow(8, input.length() - 1 - i);
decimal += (curr * mult);
}
return decimal;
}
}``````