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MODULE 3b

FINAL PART C/C++ STATEMENTS, EXPRESSIONS

AND OPERATORS 3

// bitwise operators

#include   <stdio.h>

int main()

{

     unsigned p;

    // function prototype…

    void DisplayBits(unsigned);

     printf("Enter an unsigned integer: ");

     scanf("%u", &p);

     DisplayBits(p);

     return  0;

}

// function definition…

void DisplayBits(unsigned number)

{

     unsigned q;

    // 2 byte, 16 bits position

     // operated bit by bit and hide/mask other bits

     // using left shift operator

     // start with 10000000 00000000

     unsigned DisplayMask = 1<<15;

     printf("%7u = ", number);

     for(q = 1; q < 16; q++)

     {

           // combining variable number with variable DisplayMask

            putchar(number & DisplayMask ? '1':'0');

           // number variable is left shifted one bit

            number<<= 1;

           // separate by 8 bits position (1 byte)

            if(q % 8 == 0)

            putchar(' ');

     }

     putchar('\n');

}

Output:

• Change DisplayMask = 0<<15 and & to | for inclusive OR operation and rerun the program.

• The shift general syntax:

bits to be left shifted << shift count

bits to be right shifted >> shift count

• The shift count must be non-negative and less than the number of bits required to represent the data type of the left operand.

• For example, let say the variable declaration is:

unsigned int p = 5

In binary, p = 00000000  00000101

For p<<1 in binary,

00000000  00000101 << 1  = 00000000  00001010 = 10 decimal

For p<<15 in binary,

      00000000  00000101 << 15 =  10000000  00000000 = 32768 decimal

• For right shift, while bits are shifted toward low-order position, 0 bits enter the high-order positions, if the data is unsigned.  If the data is signed and the sign bit is 0, then 0 bits also enter the high-order positions. 

• If the sign bit is 1, the bits entering high-order positions are implementation dependent, on some machines (processor architecture) 1s, and on others 0s, are shifted in. 

• The former type of operation is known as the arithmetic right shift, and the latter type is the logical right shift.  So, for portability issue, these operators should only be used on unsigned operands.

• For example:

unsigned int p = 40960, for 16 bits,

In binary, p = 10100000  00000000 

For p >> 1   in binary,

10100000 00000000 >> 1 = 01010000  00000000 = 20480 decimal

For p>>15     in binary,

10100000  00000000 >> 15 = 00000000  00000001 = 1 decimal

• A program example:

// bitwise operators

#include  <stdio.h>

// function prototype, you will learn this later

void BitwiseOp(unsigned int);

int main()

{

     unsigned int  num1, num2, num3, mask, SetBit;

     num1 = 7535;

     mask = 1;

     printf("The result of ANDing the following numbers\n");

     printf("using the bitwise AND, & is\n");

    // display in normal and binary representation

     BitwiseOp(num1);

     BitwiseOp(mask);

     printf("   ------------------------\n");

    // bitwise AND operation

     BitwiseOp(num1 & mask);

     num1 = 15;

     SetBit = 241;

     printf("\nThe result of inclusive ORing the following numbers\n");

     printf("using the bitwise inclusive OR, | is\n");

     BitwiseOp(num1);

     BitwiseOp(SetBit);

     printf("   ------------------------\n");

    // bitwise inclusive OR operation

    BitwiseOp(num1 | SetBit);

     num1 = 249;

     num2 = 299;

     printf("\nThe result of exclusive ORing the following numbers\n");

     printf("using the bitwise exclusive OR, ^ is\n");

     BitwiseOp(num1);

     BitwiseOp(num2);

    // bitwise exclusive OR operation

    printf("   ------------------------\n");

     BitwiseOp(num1 ^ num2);

     num3 = 21321;

     printf("\nThe One's complement of\n");

     BitwiseOp(num3);

     printf("          |||||||| ||||||||\n");

    // one's complement operation

     BitwiseOp(~num3);

     return 0;

}

// function definition…

void BitwiseOp(unsigned int value)

{

     unsigned int  p;

    // two 8 bits, 16 position, shift to left

     unsigned int  DisplayMask = 1 << 15;

     printf("%7u = ", value);

    // Loop for all bit...

     for(p=1; p<=16; p++)

     {

           // if TRUE set to '1', otherwise set to '0'

            putchar(value & DisplayMask ? '1':'0');

           // shift to left bit by bit

            // equal to: value << + 1 statement

            value <<= 1;

            if(p % 8 == 0)

           // put a space…

            putchar(' ');

     }

     putchar('\n');

 }

Output:

• For C++, the following is a list of the binary operators’ categories that can be used in C++ expressions.

• Furthermore in C++ the <bitset> header defines a bitset template class and two supporting template functions for representing and manipulating fixed-size sequences of bits in more efficient way.

3.12    The Comma Operator

• Frequently used as a simple punctuation mark.

• Used to separate variable declarations, functions’ arguments, etc.

• Also can acts as an operator.

• Separating two sub expressions with a comma can form an expression.

• Then, both expressions are evaluated, left evaluated first.  The entire expression evaluates as the value of the right expression.

• For example:

x  =  (a ++, b++);

• Assigns the value of b to x, then increments a, and then increments b.

• As conclusion, table 3.15 is the summary of the operators’ precedence.

• For this Table it is read from top (the highest) to bottom (the lowest).  Then if they are at the same level, we read it from left (the highest) to right (the lowest).

Program Examples and Experiments

// program copying from standard input, keyboard to standard output, console

// using pre defined functions, getchar() and putchar(), defined in stdio.h header file

#include <stdio.h>

#include <stdlib.h>

int main()

{

   int count;

   // gives some prompt...

   printf("Enter a line of text:\n");

   printf("Press \'S\' to stop.\n");

   // get character from standard input

   // store in variable count

   count = getchar();

   // while the S is not encountered...

   while(count != 'S')

   {

     // put character on the standard output

     putchar(count);

     // carry on getting character from the standard input

     count = getchar();

   }

  return 0;

}

Output:

// copying from standard input, keyboard to standard output, console

// using pre defined functions, getchar() and putchar() with End Of File, EOF.

// EOF may be system dependent

#include <stdio.h>

#include <stdlib.h>

int main()

{

    int count;

    // gives some prompt...

    printf("Enter a line of text:\n");

    printf("EOF to stop.\n");

    // get character from standard input

    // store in variable count

    count = getchar();

    // while the End Of File is not encountered...

    while(count != EOF)

    {

        // put character on the standard output

        putchar(count);

        // carry on getting character from the standard input

        count = getchar();

    }

    return 0;

}

Output:

// creating the working program skeleton…

#include <stdio.h>

int main()

{

  // printf("Some prompt here...\n");

  int count, charnum = 0;

  while ((count = getchar()) != EOF)

  {

    if(count != ' ')

    ++charnum;

  }

  printf("test the output here...\n");

  return 0;

}

Output:

// add other functionalities by following the

// simple steps in program development…

#include <stdio.h>

int main()

{

    // printf("Some prompt here...\n");

    // -----In the process: declare and initialize ----------

    // -----each variable used------------------------

    // -----Third: compile and run----------------

    // -----Fourth: If there are errors, recompile and rerun----

    // -----Finally, if there is no error, complete other part of-----

    // -----the program, such as comments etc-------------

    int count, charnum = 0, linenum = 0;

    printf("Enter several line of texts.\n");

    printf("Press Carriage Return then EOF to end.\n\n");

    // -------------First step: build the loop-----------

    // while storing the character process

    // not equal to the End Of File...

    while((count = getchar()) != EOF)

    {

        // do the character count

        if(count != ' ')

        ++charnum;

        // and the line count...

        if(count == '\n')

        {

            ++linenum;

            charnum = charnum -1;

        }

     }

    // ----------Second step: test the output---------------

    printf("The number of line = %d\n", linenum);

    printf("The number of char = %d\n", charnum);

    return 0;

}

Output:

• Program example compiled usingVC++/VC++ .Net.

// add other functionalities by following the simple steps in program development…

#include <cstdio>

int main()

{

    // printf("Some prompt here...\n");

    // -----In the process: declare and initialize ----------

    // -----each variable used------------------------

    // -----Third: compile and run----------------

    // -----Fourth: If there are errors, recompile and rerun----

    // -----Finally, if there is no error, complete other part of-----

    // -----the program, such as comments etc-------------

    int count, charnum = 0, linenum = 0;

    printf("Enter several line of texts.\n");

    printf("Press Carriage Return then EOF to end.\n\n");

    // -------------first: build the loop-----------

    // while storing the character process

    // not equal to the End Of File...

    while((count = getchar()) != EOF)

    {

        // do the character count

        if(count != ' ')

        ++charnum;

        // and the line count...

        if(count == '\n')

        {

            ++linenum;

            charnum = charnum -1;

        }

    }

    // ----------second: test the output---------------

    printf("The number of line = %d\n", linenum);

    printf("The number of char = %d\n", charnum);

    return 0;

}

Output:

• The following are program examples compiled usinggcc.

/ ******-cpoundassig.c-******* /

#include <stdio.h>

int main()

{

    int a = 10, b = 20;

    printf("Initially: a = 3, b = 4\n");

    printf("\na += b ---> a = a + b = %d\n", a+=b);

    printf("a last value = %d\n", a);

    printf("\na *= b ---> a = a * b = %d\n", a*=b);

    printf("a last value = %d\n", a);

    printf("\na -= b ---> a = a - b = %d\n", a-=b);

    printf("a last value = %d\n", a);

    printf("\na/=b ---> a = a / b = %d\n", a/=b);

    printf("a last value = %d\n", a);

    printf("\na-=(b+1)---> a = a - (b + 1) = %d\n", a-=(b+1));

    printf("a last value = %d\n", a);

    return 0;

}

[bodo@bakawali ~]$ gcc cpoundassig.c -o cpoundassig

[bodo@bakawali ~]$ ./cpoundassig

Initially: a = 3, b = 4

a += b ---> a = a + b = 30

a last value = 30

a *= b ---> a = a * b = 600

a last value = 600

a -= b ---> a = a - b = 580

a last value = 580

a/=b ---> a = a / b = 29

a last value = 29

a-=(b+1)---> a = a - (b + 1) = 8

a last value = 8

• Another example.

/* bitwise operators */

/******--bitwise.c--******/

#include   <stdio.h>

int main()

{

        unsigned p;

       /* function prototype. */

        void DisplayBits(unsigned);

        printf("Enter an unsigned integer: ");

        scanf("%u", &p);

        DisplayBits(p);

        return 0;

}

/* function definition. */

void DisplayBits(unsigned number)

{

        unsigned q;

       /* 2 byte, 16 bits position */

        /* operated bit by bit and hide/mask other bits */

        /* using left shift operator */

        /* start with 10000000 00000000 */

        unsigned DisplayMask = 1<<15;

        printf("%7u = ", number);

        for(q = 1; q < 16; q++)

        {

               /* combining variable number with variable DisplayMask */

                putchar(number & DisplayMask ? '1':'0');

               /* number variable is left shifted one bit */

                number<<= 1;

               /* separate by 8 bits position (1 byte) */

                if(q % 8 == 0)

                putchar(' ');

        }

        putchar('\n');

}

[bodo@bakawali ~]$ gcc bitwise.c -o hahahahaha

[bodo@bakawali ~]$ ./hahahahaha

Enter an unsigned integer: 10

     10 = 00000000 0000101

[bodo@bakawali ~]$ ./hahahahaha

Enter an unsigned integer: 200

    200 = 00000000 1100100

C & C++ programming tutorials

C and C++ further reading and digging:

1.       Check the best selling C/C++ books at Amazon.com.

2.       The source code for this Module is:Module 3 C/C++ source codes. and the related worksheet for your practice is:C lab worksheets.

|< C/C++ Statements, Expressions & Operators 2 | Main | Let Have A Break! >|Site Index |Download |

C and C++ Statements, Expressions & Operators: Part 1 | Part 2 | Part 3 |