How to set a perticular bit in a given byte?

[kedar1979]

I have a character byte.I have to set any bit from it to 1.I am passing a bit position through a function say set_bits(bit_position) .Now give me a c code for this.Also i want to reset this bit again to 0, how can I do it.?

[horace1]

you use the bit operators | (OR) to set a bit and & (AND) to reset a bit, e.g. the program

// set and reset bits
#include <stdio.h>
int main()
{
    int y=0;
    printf("y=%x \n", y);
    y = y | 1;        // set bit 0
    printf("y=%x \n", y);
    y = y | 8;       // set bit 3
    printf("y=%x \n", y);
 
    int x=0xff;
    printf("x=%x \n", x);
    x = x & ~1;        // clear bit 0
    printf("x=%x \n", x);
    x = x & ~8;       // clear bit 3
    printf("x=%x \n", x);
 return 0;
} 
 

when run gives the output
y=0
y=1
y=9
x=ff
x=fe
x=f6

[kedar1979]

Thanks....but could you please explain it in detail..?

[horace1]

The following truth table shows the logical operations AND, OR (inclusive or) and EOR (exclusive or) on two bits A and B:

 
           +----------------------------------+
           ¦  A  ¦  B  ¦  AND  ¦  OR  ¦  EOR  ¦
           +-----+-----+-------+------+-------¦
           ¦  0  ¦  0  ¦   0   ¦  0   ¦   0   ¦
           ¦  0  ¦  1  ¦   0   ¦  1   ¦   1   ¦
           ¦  1  ¦  0  ¦   0   ¦  1   ¦   1   ¦
           ¦  1  ¦  1  ¦   1   ¦  1   ¦   0   ¦
           +----------------------------------+
 

& bitwise and operator& bitwise and operatorThe C bitwise logical operators & (and), | (or) and ^ (exclusive or) have two integral operands and perform the specified operation upon the corresponding bits in each operand.

    k = i & j;      /* logical AND, i & j, assign result to k */ 
    k = i | j;       /* logical inclusive OR, i | j, assign result to k */
    k = i ^ j;       /* logical exclusive OR, i ^ j, assign result to k */
 

For example, assuming that i and j are byte sized variables having the values 00001010 and 01001100 respectively, the following table shows the result of &, | and ^ operations.

+------------------------------------------------------------+
¦  operation   ¦  operator  ¦  example operation  ¦  result  ¦
+--------------+------------+---------------------+----------¦
¦     AND      ¦   i & j    ¦ 00001010 & 01001100 ¦ 00001000 ¦ 
¦              ¦            ¦                     ¦          ¦ 
¦ inclusive OR ¦   i | j    ¦ 00001010 | 01001100 ¦ 01001110 ¦ 
¦              ¦            ¦                     ¦          ¦ 
¦ exclusive OR ¦   i ^ j    ¦ 00001010 ^ 01001100 ¦ 01000110 ¦
+------------------------------------------------------------+    
 

e.g. a program to set bits

#include <stdio.h>
int main()
{
    int bit, z=0;;
     while(1)
      {
      printf("enter bit to set ? ");
      scanf("%d", &bit);
      z = z | (1 << bit);
      printf("z=%x \n", z);
      } 
 return 0;
}
 

the loop
1. read the bit number, e.g. 5
2. shift 1 left by that number of bits, e.g. 0x20
3. OR it into z

a run gave:
enter bit to set ? 5
z=20
enter bit to set ? 0
z=21

Another bitwise operator is unary ~ (not or one's complement) which inverts the value of every bit in the operand, i.e. 0 becomes 1 and 1 becomes 0, e.g. for 00001010 the one's complement would be 11110101

i = ~i

[kedar1979]

Thank you so much......keep in touch.......bye for now

[check]

hi

i have a interview on 2/may.

i want the code for setting any bit i tried the above probs but its not running .

i request u to plz send the correct n running code with explanation

plz send it as soon as possible. on [e-mail]

bye