How this program work?

Question

1.00/5 (1 vote)

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C

#include<stdio.h>
int main()
{
    char c = 255;
     c = c +10;
     printf("%d",c);
}

What I have tried:

Why this program give me result 9

Posted 3-Apr-22 20:44pm

Fardin Khan_451

Updated 3-Apr-22 22:34pm

CPallini

v2

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M Imran Ansari 4-Apr-22 3:09am

You are storing into character and calculating arithmetic operation, which is calculating as per ASCII values. What is your expected output? You

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OriginalGriff · Accepted Answer · 2022-04-03T22:10:00

T0 add to what CPallini said, in C a char value is an 8-bit quantity, so it can hold values from 00000000 binary to 11111111 binary inclusive, and no other. If you add one to a value that contains 11111111 binary, it "rolls over" to 00000000 binary.

Conventionally, C char values are signed, which means that the most significant bit of the value controls if it is positive or negative - a '1' in the "top bit" indicates a negative number: 01111111 binary is 127 in decimal, 10000000 binary is -128 in decimal, and 11111111 binary is -1 in decimal.

So if you start with a char containing 255 and add 10 to it, what you are actually doing is adding 10 to -1:

decimal             binary
x = 10 + (-1)       x = 00001010 + 11111111
x = 10 - 1          x = 00001001
             x = 9

Make sense now?

CPallini · Accepted Answer · 2022-04-03T21:10:00

Solution 1

Variable c range is [-128..+127] hence 255 is out of range. In such a case the behaviour is 'implementation-defined'. In your program c is actually initialized with -1.

Posted 3-Apr-22 21:10pm