[2 days left] What’s wrong with your cloud strategy? Learn why multicloud solutions matter with Nimble Storage.Register Now

x
?
Solved

what actually happens when a character c is assigned a value of 164?

Posted on 2003-11-05
7
Medium Priority
?
235 Views
Last Modified: 2010-04-15
Hello,

what happens when the folloowing:

char x = 64;
x+=100;
cout << (int)c ;

it prints -92
but the question is how ? how does it work internally? how does it arrive at -92?

thanks and regards
Raghu
0
Comment
Question by:rags2k
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
7 Comments
 
LVL 48

Expert Comment

by:AlexFM
ID: 9688536
Replace char to unsigned char.
0
 
LVL 5

Expert Comment

by:mtmike
ID: 9688750
Two's complement arithmetic.

For example (or use google):
http://www.hal-pc.org/~clyndes/computer-arithmetic/twoscomplement.html
0
 

Accepted Solution

by:
linuxsub earned 80 total points
ID: 9688897
x becomes 164.
164==0xA4==10100100B
In 2' s complement, it becomes:
10100100B=(-01011011B - 1) = -92

The way 2's complement works for signed values is, if the Most significant bit is 1, sign becomes negative(-), and get the absolute value by calculating  bitwise NOT of the current value and adding one to it (since there is nothing called -0).

As AlexFM says, using unsigned char should give you 164.
0
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

 
LVL 16

Expert Comment

by:imladris
ID: 9690519
What you need to note is that char is a one byte quantity. In 1 byte (8 bits) you can count from 0 through 255 if you consider it unsigned. But if you consider it signed, you can count from -128 to 127. So when you added 100 to x it became 0xA4, as linuxsub indicates. So this was now a 1 byte quantity with a decimal value of -92, that is, it had overflowed, because a 1 byte signed quantity cannot represent 164. *After* that, you cast it to an int. An int is also signed, and so the cast will "propogate" the sign bit during the conversion (in order to preserve the value; it was -92 before the cast, and this way it will also be -92 after the cast). Assuming a 4 byte int, you would get 0xFFFFFFA4.

You can solve this, as indicated, by using an unsigned char. That will allow you to represent 0 through 255.

More messily, you could also, of course force it to do what you want by masking off the top bits:

cout<<((int)c&0xff;

0
 
LVL 6

Expert Comment

by:Ajar
ID: 9692753
char can store values between  -128  to +127  and
164  = 10100100    in binary
The left most bit the sign bit is turned on meaning the number is negative
the rest of the number is   0100100  
now as the number  is negative so its stored as two's compilent  so its value becomes

 ~ 0100100] =>   1011011  +1  =>        1011100  
=>  -92
0
 
LVL 16

Expert Comment

by:imladris
ID: 9702235
Did any of those answers help?

If so, it is now time to choose and answer and grade it.

If not, perhaps a clarifying question would help.
0
 

Author Comment

by:rags2k
ID: 9703641
All answers helped me but the first and most useful one tome was one by linuxsub..bu i am surprised that I am not allowed to accept/rate all answers on their merits...
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
Summary: This tutorial covers some basics of pointer, pointer arithmetic and function pointer. What is a pointer: A pointer is a variable which holds an address. This address might be address of another variable/address of devices/address of fu…
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use while-loops in the C programming language.
The goal of this video is to provide viewers with basic examples to understand how to create, access, and change arrays in the C programming language.
Suggested Courses

656 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question