[英]iProblems with substr, integers and loops in converting decimal to binary and binary to decimal
I wrote this program for someone who wanted it without using of ToBinaryString and ToString methods. 我为不需要使用ToBinaryString和ToString方法的人编写了该程序。 I wrote the app, but it doesn't work!
我编写了该应用程序,但是它不起作用! If I do Dec2Bin, it gives me null!
如果我执行Dec2Bin,它将给我空值! and if I do Bin2Dec it gives me String out of index: -1!
如果我执行Bin2Dec,它将使我的字符串超出索引:-1! Can someone help me fix it?
有人可以帮我解决吗?
Code: 码:
package decimalBinary;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class DecBin {
public static void main(String[] args) throws NumberFormatException, IOException {
int conargs1,conargs2;
// conargs1 is input
// conargs2 is mode, if = 1 then dec2bin, if = 2 then bin2dec
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter number: ");
conargs1=Integer.parseInt(br.readLine());
System.out.println("Enter mode: ");
conargs2 = Integer.parseInt(br.readLine());
System.out.println(conargs2==1 ? "Dec2Bin" : (conargs2==2 ? "Bin2Dec" : "none"));
if (args.length == 2){ // TO BINARY
if(conargs2==1){
System.out.println(DecBin.dec2bin(String.valueOf(conargs1)));
}else if (conargs2==2){ // TO DECIMAL
System.out.println(DecBin.bin2dec(String.valueOf(conargs1)));
}
System.exit(0);
}
}
public static String dec2bin(String arg){
String out = null;
String tmp;
long i, x;
int maxpower = 30;
x = Long.parseLong(arg);
if (x == 0){
return "0";
}else if (x > 0){ // positive decimals
if (x > Math.pow(2, maxpower)) {
return "should be no larger than " + String.valueOf(2 ^ maxpower);
}
out = "";
for(i = maxpower+1; i <= 0; i--){
if (x % (Math.pow(2, i))==0){
out = out + "1";
}else{
out = out + "0";
}
}
}else{ // negative decimals
x = -x;
x = Math.abs(x);
if (x > Math.pow(2, maxpower)) {
return "should be no larger than " + String.valueOf(2 ^ maxpower);
}
out = "";
for(i = maxpower+1; i <= 0; i--){ // Inverted Binary
if (x % (Math.pow(2, i))==0){
out = out + "0";
}else{
out = out + "1";
}
}
x = DecBin.bin2dec(out)+1;
out= "";
for(i = maxpower+1; i <= 0; i--){
if (x % (Math.pow(2, i))==0){
out = out + "1";
}else{
out = out + "0";
}
}
}
return out;
}
public static long bin2dec(String arg){
// If it was a positive number.
long dec = 0; // initializing decimal number
long length = arg.length(); // length of our binary string
char temp;
//long charplace;
long lengthofchar = 1;
long x = 0;
if (arg.length() <= 0){return 0;}
for (x = 0; x <= length; x++) {
// charplace = 0;
// charplace = -x;
// charplace += -1;
// charplace += arg.length();
// charplace = Long.sum(charplace, 5);
// charplace -= lengthofchar;
// charplace--;
temp = arg.charAt(arg.length()-x-1);
// length = length - 1;
if (temp != '0') {
dec += Math.pow(2 , x - 1);
}
}
return dec;
}
}
This is the error I'm getting when using bin2dec: 这是我在使用bin2dec时遇到的错误:
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The method charAt(int) in the type String is not applicable for the arguments (long)
at decimalBinary.DecBin.bin2dec(DecBin.java:98)
at decimalBinary.DecBin.main(DecBin.java:22)
Before this, I have used int
type for variables, but I got String out of Index: -1
in the line I've used charAt. 在此之前,我已经将
int
类型用于变量,但是在使用charAt的那一行中,我String out of Index: -1
中得到了String out of Index: -1
。 I've also used substr before that and I got the same error! 在此之前,我还使用过substr,并且遇到了同样的错误!
EDIT: If I use temp = arg.charAt(Integer.parseInt(String.valueOf(arg.length()-x-1)));
编辑:如果我使用
temp = arg.charAt(Integer.parseInt(String.valueOf(arg.length()-x-1)));
I will get this error: 我会收到此错误:
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
at java.lang.String.charAt(Unknown Source)
at decimalBinary.DecBin.bin2dec(DecBin.java:98)
at decimalBinary.DecBin.main(DecBin.java:22)
There is a problem with your for loop
inequality statements, namely: 您的
for loop
不平等语句存在问题,即:
In your dec2bin
method: for(i = maxpower+1; i <= 0; i--)
should be for(i = maxpower+1; i >= 0; i--)
because you will never enter the loop and you print the default value for out
which is null
. 在您的
dec2bin
方法中: for(i = maxpower+1; i <= 0; i--)
应该是for(i = maxpower+1; i >= 0; i--)
因为您将永远不会进入循环并且您打印默认值out
这是null
。
In your bin2dec
method: for (x = 0; x <= length; x++)
should be for (x = 0; x < length; x++)
because temp = arg.charAt(arg.length()-x-1);
在您的
bin2dec
方法中: for (x = 0; x <= length; x++)
应该是for (x = 0; x < length; x++)
因为temp = arg.charAt(arg.length()-x-1);
can be -1
at the end of your loop. 在循环结束时可以为
-1
。
*After your updated question with the error stacktrace, use int
instead of long
for your variables or else you need casting to int
for charAt
to work. *在更新了有关错误stacktrace的问题之后,请对变量使用
int
而不是long
,否则您需要将其强制转换为int
以便charAt
起作用。
Finally, I've managed to edit my code :) 最后,我设法编辑了代码:)
Thanks to Konstantinos Chalkias I found out what I had to do :D 感谢Konstantinos Chalkias,我找到了必须要做的:D
This is the final class (that works very good!): 这是最后一堂课(效果非常好!):
package decimalBinary;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class DecBin {
public static void main(String[] args) throws NumberFormatException, IOException {
int conargs1,conargs2;
// conargs1 is input
// conargs2 is mode, if = 1 then dec2bin, if = 2 then bin2dec
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter number: ");
conargs1=Integer.parseInt(br.readLine());
System.out.println("Enter mode: ");
conargs2 = Integer.parseInt(br.readLine());
System.out.println(conargs2==1 ? "Dec2Bin" : (conargs2==2 ? "Bin2Dec" : "none"));
if (args.length == 2){ // TO BINARY
if(conargs2==1){
System.out.println(DecBin.dec2bin(String.valueOf(conargs1)));
}else if (conargs2==2){ // TO DECIMAL
System.out.println(DecBin.bin2dec(String.valueOf(conargs1)));
}
System.exit(0);
}
}
public static String dec2bin(String arg){
String out = null;
String tmp;
long i, x;
int maxpower = 30;
x = Integer.parseInt(arg);
if (x == 0){
return "0";
}else if (x > 0){ // positive decimals
if (x > Math.pow(2, maxpower)) {
return "should be no larger than " + String.valueOf(2 ^ maxpower);
}
out = "";
int binary[] = new int[30];
int index = 0;
while(x > 0){
binary[index++] = (int) (x % 2);
x = x/2;
}
for(i = index-1;i >= 0;i--){
out = out+binary[(int) i];
}
}else{ // negative decimals
// x = -x;
x = Math.abs(x); // convert positive of decimal to binary
if (x > Math.pow(2, maxpower)) {
return "should be no larger than " + String.valueOf(2 ^ maxpower);
}
long xBinaryPositive;
xBinaryPositive = Long.parseLong(DecBin.dec2bin(String.valueOf(x)));
String xBinaryInverted;
out = "";
xBinaryInverted = String.valueOf(xBinaryPositive).replace('0', '2').replace('1', '0').replace('2', '1');
long xBinaryInvertedIntVal;
xBinaryInvertedIntVal = DecBin.bin2dec(xBinaryInverted);
out = DecBin.dec2bin(String.valueOf(xBinaryInvertedIntVal+1));
}
return out;
}
public static long bin2dec(String binaryInput){
long binary = Long.parseLong(binaryInput);
long decimal = 0;
long power = 0;
while(true){
if(binary == 0){
break;
} else {
long tmp = binary % 10;
decimal += tmp * Math.pow(2, power);
binary = binary/10;
power++;
}
}
return decimal;
}
}
In final code, I used while
instead of for
. 在最终代码中,我使用
while
代替for
。
I found much of this code in Java2Novice's Interview Programs . 我在Java2Novice的Interview Programs中找到了很多这样的代码。 Many thanks to them for those codes.
非常感谢他们提供这些代码。
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