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C++ binary and decimal conversion

Posted on 2013-06-23
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Last Modified: 2013-06-24
I am looking for a good way for the following conversion in C++:

41283 is binary digit “1010000101000011”
From first bit,
Structure ID:101¿5 (decimal)
Item No.:0000101¿5 (decimal)
Route No:000011¿3 (decimal)

Thank you.
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Question by:cytello
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Author Comment

by:cytello
ID: 39269979
Sorry about the strange characters

1. I need to convert 41283 to binary as 1010000101000011
2. convert the first 3 bits 101 to decimal
3. convert the next 7 bits 0000101 to decimal
4. convert the next 6 bits 000011 to decimal

Is there a way to get the decimal values for the 3 bits, 7 bits, and 6 bits?
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Expert Comment

by:jkr
ID: 39270179
If you only want to read that data (and not write it), a simple bit shifting/masking approach will do - otherwise I'd point you to 'bitsets' (http://www.cplusplus.com/reference/bitset/bitset/) or 'bitfields' (http://en.wikipedia.org/wiki/Bit_field). But, in your case, that can be done like

short int val = 41283; // 16 bits

short int structID = (val & 0x1c00) >> 13;
short int itemNo = (val & 0x01fc0) >> 6;
short int routeNo = val & 0x003f;

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by:lomo74
ID: 39270533
the opposite procedure would be:
unsigned short int val1, val2, val3, num;
val1 = 5;
val2 = 5;
val3 = 3;
num = (val1 & 0x07) << 13 |
	(val2 & 0x7F) << 6 |
	(val3 & 0x3F);

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frankhelk earned 500 total points
ID: 39270740
And here the elegant (bitfields) way to let the compiler sort the stuff out:
#include <stdio.h>

typedef union 
{
	short value;
	struct
	{   // stacked backwards !
		unsigned int RouteNo:6;
		unsigned int itemNo:7;
		unsigned int structId:3;
	} fields;
} bitfield;


int main()
{
	bitfield val;

	val.value = 41283;

	printf("StructID : %d\n", val.fields.structId);
	printf("ItemNo   : %d\n", val.fields.itemNo);
	printf("RouteNo  : %d\n", val.fields.RouteNo);

	return 0;
}

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Easier to understand, and more simple to use thruout the code. And more easy to handle if the coding of the bitfield changes.

Output would be
StructID : 5
ItemNo   : 5
RouteNo  : 3

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Expert Comment

by:lomo74
ID: 39270770
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Expert Comment

by:sarabande
ID: 39271832
cytello, is it homework?

if yes, you may post the complete assignment such that we could help you to writing your own code.

generally, converting a string number from one base to another (in your sample it is from base 2 to base 10), you easily could do it by extracting each digit from right to left, convert the digit to number, multiply it with the base^n  (where n is a loop counter beginning at 0) and add the result to the total.

for '110' you would get 0*2^0 + 1*2^1 + 1*2^2 = 0 + 2 + 4 = 6.

Sara
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Author Closing Comment

by:cytello
ID: 39271927
Thank you.
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