How to Convert Binary String Value to Decimal

How to convert binary string value to decimal

Use Integer.parseInt (see javadoc), that converts your String to int using base two:

int decimalValue = Integer.parseInt(c, 2);

How to convert binary string to decimal?

The parseInt function converts strings to numbers, and it takes a second argument specifying the base in which the string representation is:

var digit = parseInt(binary, 2);

See it in action.

How to convert a binary String to a decimal string in Java

To convert a base 2 (binary) representation to base 10 (decimal), multiply the value of each bit with 2^(bit position) and sum the values.

e.g. 1011 -> (1 * 2^0) + (1 * 2^1) + (0 * 2^2) + (1 * 2^3) = 1 + 2 + 0 + 8 = 11

Since binary is read from right-to-left (i.e. LSB (least significant bit) is on the rightmost bit and MSB (most-significant-bit) is the leftmost bit), we traverse the string in reverse order.

To get the bit value, subtract '0' from the char. This will subtract the ascii value of the character with the ascii value of '0', giving you the integer value of the bit.

To calculate 2^(bit position), we can keep a count of the bit position, and increment the count on each iteration. Then we can just do 1 << count to obtain the value for 2 ^ (bit position). Alternatively, you could do Math.pow(2, count) as well, but the former is more efficient, since its just a shift-left instruction.

Here's the code that implements the above:

public static int convertBinStrToInt(String binStr) {
    int dec = 0, count = 0;
    for (int i = binStr.length()-1; i >=0; i--) {
        dec += (binStr.charAt(i) - '0') * (1 << count++);
    }

    return dec;
}

Convert binary string to binary or decimal value

You could use the packBits function (in the base package). Bear in mind that this function requires very specific input.

(yy <- intToBits(5))
#  [1] 01 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
# [26] 00 00 00 00 00 00 00
# Note that there are 32 bits and the order is reversed from your example

class(yy)
[1] "raw"

packBits(yy, "integer")
# [1] 5

There is also the strtoi function (also in the base package):

strtoi("00000001001100110000010110110111", base = 2)
# [1] 20121015

strtoi("000101", base = 2)
# [1] 5

Java converting binary string to decimal

Here is where your code went wrong:

str.charAt(16-1 - i) * Math.pow(2, i);

You just multiplied a char by a double. This will evaluate to the ASCII value of char times the double, not 0 or 1.

You need to convert this to an integer first:

Integer.parseInt(Character.toString(str.charAt(16-1 - i))) * Math.pow(2, i)

Or, you can just:

Integer.parseInt(binaryString, 2)

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