Exercise 2.3 (Completed)

1. (Practice) State whether the following variable names are valid. 
If they’re invalid, state the reason.
prod_a           valid
newbal           valid
9ab6             invalid (begins with a number)
c1234            valid
while            invalid (C++ keyword)
sum.of           invalid (decimal point not allowed)
abcd             valid
$total           invalid (begins with special character)
average          valid
_c3              invalid (begins with special character)
new bal          invalid (contains a space)
grade1           valid
12345            invalid (begins with a number)
a1b2c3d4         valid
finGrad          valid

2. (Practice) State whether the following variable names are valid. If they’re invalid, state the
reason. Also, indicate which of the valid variable names shouldn’t be used because they convey
no information about the variable.
salestax       valid
harry          valid (not meaningful)
maximum        valid
3sum           invalid (begins with a number)
a243           valid (not meaningful)
sue            valid (not meaningful)
okay           valid
for            invalid (C++ keyword)
r2d2           valid (not meaningful)
c3p0           valid (not meaningful)
a              valid (not meaningful)
tot.al         invalid (contains decimal point)
firstNum       valid
average        valid
awesome        valid (not meaningful)
c$five         invalid (contains a special character)
cc_al          valid (not meaningful)sum            valid
goforit        valid (not meaningful)
netpay         valid
3. (Practice) 
a. Write a declaration statement to declare that the variable count will be used to
store an integer.
-----int count;
b. Write a declaration statement to declare that the variable grade will be used to store a
floating-point number.
-----float grade;
c. Write a declaration statement to declare that the variable yield will be used to store a
double-precision number.
-----double yield;
d. Write a declaration statement to declare that the variable initial will be used to store a
character.
-----char initial;
4. (Practice) Write a single declaration statement for each set of variables:
a. num1, num2, and num3 used to store integer numbers
int num1, num2, num3;
b. grade1, grade2, grade3, and grade4 used to store double-precision numbers
double grade1, grade2, grade3;
c. temp1, temp2, and temp3 used to store double-precision numbers
double temp1, temp2, temp3;
d. let1, let2, let3, and let4 used to store characters
char let1, let2, let3, let4;
5. (Practice) Write a single declaration statement for each set of variables:
a. firstnum and secnum used to store integers
int firstnum, secnum;
b. price, yield, and coupon used to store double-precision numbers
double price, yield, coupon
c. average used to store a double-precision number
double average;
6. (Modify) Rewrite each of these declaration statements as three separate declarations:
a. int month, day = 30, year;
int month;
int day = 30;
int year;
b. double hours, volt, power = 15.62;
double hours;
double volt;
double power = 15.62;
c. double price, amount, taxes;
double price;
double amount;
double taxes;
d. char inKey, ch, choice = 'f';
char inKey;
char ch;
char choice = 'f';
7. (Desk check) 
a. Determine what each statement causes to happen in the following program:
 #include <iostream>         // include standard input and output 
using namespace std;        // using the standard library 
int main()                 //  beginning of main function
{
  int num1, num2, total;   // declartion of num1, num2, total
  num1 = 25;               // assigning value to num1
  num2 = 30;               // assigning value to num 2
  total = num1 + num2;     // algorithm for the function
  cout << “The total of ” << num1 << “ and “  // Displays num1 and num 2
       << num2 << “ is “ << total << endl;    // the total is displayed using the simple algorithm
  return 0; // returns nothing to the console
}

b. What output will be displayed when the program in Exercise 7a runs?
The total of 25 and 30 is 55
8. (Program) Write a C++ program that stores the sum of the integer numbers 12 and 33 in a
variable named sum. Have your program display the value stored in sum.
#include <iostream>
using namespace std;
int main()
{
int sum;
sum = 12 + 33;
cout << "Displaying the value of sum" << sum << endl;
return 0;
}

9. (Program) Write a C++ program that stores the integer value 16 in the variable length and
the integer value 18 in the variable width. Have your program calculate the value assigned to
the perimeter variable, using this formula:
perimeter = 2 × (length + width)
Your program should then display the value stored in perimeter. Be sure to declare all variables
as integers at the beginning of the main() function.
#include <iostream>
using namespace std;
int main()
{
int length, width;
length = 16;
width = 18;
perimeter = 2 *(length + width);
cout << "Displaying the value stored in perimeter" << perimeter << endl;
return 0;
}
10. (Program) Write a C++ program that stores the integer value 16 in the variable num1 and the
integer value 18 in the variable num2. (Be sure to declare the variables as integers.) Have your
program calculate the total of these numbers and their average. Store the total in an integer
variable named total and the average in an integer variable named average. (Use the statement
average = total/2.0; to calculate the average.) Use a cout statement to display the
total and average.
#include <iostream>
using namespace std;
int main()
{
int num1 =16;
int num2 = 18;
total = num1 + num2;
average = total/2;
return 0;
}
11. (Debug) Enter, compile, and run the following program. Determine why an incorrect average
is displayed and correct the error.
#include <iostream>
using namespace std;
int main()
{
  int num1 = 15;
  int num2 = 18;
  int total, average;
  total = num1 + num2;
  average = total / 2.0;
  cout << “The average of “ << num1
       << “ and “ << num2 << “ is “ 
8       << average << endl;
  return 0;
}
-------------------Corrected below-----------------------------
#include <iostream>
using namespace std;
int main()
{
  float num1 = 15;
  float num2 = 18;
  float total, average;
  total = num1 + num2;
  average = total / 2.0;
  cout << “The average of “ << num1
       << “ and “ << num2 << “ is “ 
       << average << endl;
  return 0;
}
*The output for this particular situation requires a floating point declartion in order to produce the desired result.

12. (Debug) The following program was written to correct the error produced by the program in
Exercise 11. Determine why this program also doesn’t provide the correct result and correct
the error.
#include <iostream>
using namespace std;
int main()
{
  int num1 = 15;
  int num2 = 18;
  int total;
  double average;
  total = num1 + num2;
  average = total / 2;
  cout << “The average of “ << num1
       << “ and “ << num2 << “ is “ 
       << average << endl;
  return 0;
}
-------------------------------------------
#include <iostream>
using namespace std;
int main()
{
  int num1 = 15;
  int num2 = 18;
  double total;
  double average;
  total = num1 + num2;
  average = total / 2;
  cout << “The average of “ << num1
       << “ and “ << num2 << “ is “ 
       << average << endl;
  return 0;
}
*The varable total should be declared a floating point. 

13. (Program) Write a C++ program that stores the number 105.62 in the variable firstnum,
89.352 in the variable secnum, and 98.67 in the variable thirdnum. (Be sure to declare the
variables first as float or double.) Have your program calculate the total of the three numbers
and their average. The total should be stored in the variable total and the average in the
variable average. (Use the statement average = total /3.0; to calculate the average.)
Use a cout statement to display the total and average.
---------------------------------------------------------
#include <iostream>
using namespace std;
{
float firstnum = 105.62;
float secnum = 89.352;
float thirdnum = 98.67;
total = firstnum + secnum + thirdnum;
average = total/3.0;
cout << "The total and average of hidden code is" << total << average << endl;
return 0;

}

14. (For thought) a. A statement used to clarify the relationship between squares and rectangles
is “All squares are rectangles but not all rectangles are squares.” Write a similar statement that
describes the relationship between definition and declaration statements.

"All definitions are declarations but not all declarations are definitions."

b. Why must a variable be defined before any other C++ statement that uses the variable?

A variable must be defined in order to have a value to act upon. 

Note for Exercises 15 to 17: Assume that a character requires 1 byte of storage, an integer requires
4 bytes, a single-precision number requires 4 bytes, and a double-precision number requires 8 bytes.
Variables are assigned storage in the order they’re declared. (Review Section 2.6 if you’re unfamiliar
with the concept of a byte.) Refer to Figure 2.7 for these exercises.
Addresses
159 160 161 162 163 164 165 166
167 168 169 170 171 172 173 174
175 176 177 178 179 180 181 182
183 184 185 186 187 188 189 190
Figure 2.7 Memory bytes for Exercises 15 to 17

15. (Practice) a. Using Figure 2.7 and assuming the variable name rate is assigned to the byte
at memory address 159, determine the addresses corresponding to each variable declared in
the following statements. Also, fill in the correct number of bytes with the initialization data
included in the declaration statements. (Use letters for the characters, not the computer codes
that would actually be stored.)
float rate;
char ch1 = 'M', ch2 = 'E', ch3 = 'L', ch4 = 'T';
double taxes;
int num, count = 0;

rate = 159,160,161,162
ch1 = 163
ch2 = 164
ch3 = 165
ch4 = 166
taxes =167,168,169,170,171,172,173,174
num = 175,176,177,178
count = 179,180,181,182

b. Repeat Exercise 15a, but substitute the actual byte patterns that a computer using the
ASCII code would use to store characters in the variables ch1, ch2, ch3, and ch4. (Hint : Use
Table 2.2.)
ch1 = 01001101
ch2 = 01000101
ch3 = 01001100
ch4 = 01010100

16. (Practice) a. Using Figure 2.7 and assuming the variable named cn1 is assigned to the byte
at memory address 159, determine the addresses corresponding to each variable declared in
the following statements. Also, fill in the correct number of bytes with the initialization data
included in the declaration statements. (Use letters for the characters, not the computer codes
that would actually be stored.)
char cn1 = 'P', cn2 = 'E', cn3 = 'R', cn4 = 'F', cn5 = 'E';
char cn6 = 'C', cn7 = 'T', key = '\\', sch = '\'', inc = 'A';
char inc1 = 'T';

cn1 = 159
cn2 = 160
cn3 = 161
cn4 = 162
cn5 = 163
cn6 = 164
cn7 = 165
key = 166
sch = 167
inc = 168
inc1 = 169

b. Repeat Exercise 16a, but substitute the actual byte patterns a computer using the ASCII
code would use to store characters in each declared variable. (Hint: Use Tables 2.2 and 2.3.)

cn1 = 01010000
cn2 = 01000101
cn3 = 01010010
cn4 = 01000110 
cn5 = 01000101
cn6 = 01000011
cn7 = 01010100
key = 01011100
sch = 00100111
inc = 01000001
inc1 = 01010100

17. (Practice) Using Figure 2.7 and assuming the variable name miles is assigned to the byte at
memory address 159, determine the addresses corresponding to each variable declared in the
following statements:
float miles;
int count, num;
double dist, temp;

miles = 159,160,161,162
count = 163,164,165,166
num = 167,168,169,170
dist = 171,172,173,174,175,176,177,178
temp = 179,180,181,182,183,184,185,186