Looping
Example: MAX of three numbers
int num1, num2, num3, max;
cin >> num1 >> num2 >> num3;
if ( num1 > num2 )
if ( num1 > num3 )
max = num1;
else
max = num3;
else
if ( num2 > num3 )
max = num2;
else
max = num3;
max = num1;
if ( num2 > max )
max = num2;
if ( num3 > max )
max = num3;
How about finding the MAX of n number?
cout << “The max value is ” << max << endl;
Example: MAX of n numbers
 pseudo-code:
 read 1st number
 max = 1st number
 while not the end
read a number
if the new number is larger than max,
then max = new number
 How do we know it is the end?
 use -1 to indicate the end.
 What if the first input is -1?
int num, max;
cin >> num;
if ( num == -1 )
{
cout << “No input!”;
return 0;
}
max = num;
while ( num != -1 )
{
if ( num > max )
max = num;
cin >> num;
}
cout << “The max value is ”
<< max << endl;
return 0;
Loop Control Variable (LCV)
 when to exit a loop
 avoid infinite loops
 LCV: num
cin >> num;
max = num;
while ( num != -1 )
{
if ( num > max )
max = num;
cin >> num;
}
Four parts of a loop
 Loop initialization
 LCV and others
 Testing LCV
 Loop Body
 do the work
 LCV update
cin >> num;
max = num;
while ( num != -1 )
{
if ( num > max )
max = num;
cin >> num;
}
While Loop
Initialization (LCV and others)
while (LogicalExpression)
(Testing LCV)
false
true
Do Work
Statement after loop
Update LCV
Example: MAX of n numbers within [0,50]
const int LOW_BOUND = 0;
const int UP_BOUND = 50;
const int END_VALUE = -1;
int num, max;
cin >> num;
if ( num == END_VALUE )
{
cout << “No input!”;
return 0;
}
max = num;
while ( num != END_VALUE )
{
if ( num >= LOW_BOUND && num <= UP_BOUND )
{
}
if ( num > max )
max = num;
else
cout << “Out of range!” << endl;
cin >> num;
}
cout << “The max value is ” << max << endl;
return 0;
Is this correct?
else is paired with the closest if.
Getting Valid Values
Pseudo Code
Input a value
While the input value is out of range
Display a message
Input a new value
cin >> score;
while ( score < 0 || score > 50 )
cout << “Invalid score!”;
cin >> score;
//Correct?
Getting Valid Values
Pseudo Code
Input a value
While the input value is out of range
Display a message
Input a value
cin >> score;
while ( score < 0 || score > 50 )
{
cout << “Invalid score!”;
cin >> score;
}
//How about the end value -1?
Getting Valid Values
Pseudo Code
Input a value
While the input value is out of range and not -1
Display a message
Input a value
cin >> score;
while ( ( score < 0 || score > 50) && score != -1 )
{
cout << “Invalid score!”;
cin >> score;
}
// Can we have
while (score < 0 || score > 50 && score != -1)
// NO! It’s the same as the following:
while (score < 0 || (score > 50 && score != -1))
Getting Valid Scores
const int LOW_BOUND = 0;
const int UP_BOUND = 50;
const int END_VALUE = -1;
int num, max;
cin >> num;
while ((num < LOW_BOUND || num > UP_BOUND) && num!= END_VALUE)
{
cout << “Invalid number!” << endl;
cin >> num;
}
if ( num == END_VALUE )
{
cout << “No input!” << endl;
return 0;
}
max = num;
while ( num != -1 )
{
if ( num > max )
max = num;
cin >> num;
while ( num != END_VALUE && (num < LOW_BOUND|| num > UP_BOUND))
{
cout << “Invalid number!” << endl;
cin >> num;
}
}
cout << “The max value is ” << max << endl;
return 0;
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Three Types of Loops
 Sentinel-controlled loop
 the loop stops when LCV become certain value.
while ( LCV != END_VALUE )
 Count-controlled loop
 the loop executes LIMIT times.
while ( count <= LIMIT )
 End-of-file-controlled loop
 the loops stops when reaching the end of the input file.
while ( !cin.eof() )
AVERAGE of 10 numbers
Pseudo Code
While count is not 10 yet
input a number
add the number to total
increase count by 1
average = total / count
AVERAGE of 10 numbers
const int LIMIT
= 10;
int main()
{
float num, total = 0, average;
int count = 0;
cout << "Please input " << LIMIT << " numbers: " << endl;
while ( count < LIMIT )
{
cin >> num;
total += num;
count ++;
}
// total = total + num;
// count = count + 1;
average = total / count;
cout << "The average is " << average << "." << endl;
return 0;
}
AVERAGE of 10 numbers
const int LIMIT
= 10;
int main()
{
float num, total = 0, average;
int count;
cout << "Please input " << LIMIT << " numbers: " << endl;
cin >> num;
count = 1;
while ( count < LIMIT )
{
total += num;
cin >> num;
count ++;
}
How about this design?
Wrong! sum 9 numbers / 10
How to fix it?
average = total / count;
cout << "The average is " << average << "." << endl;
return 0;
}
AVERAGE of 10 numbers
const int LIMIT
= 10;
int main()
{
float num, total = 0, average;
int count;
cout << "Please input " << LIMIT << " numbers: " << endl;
cin >> num;
count = 0;
while ( count < LIMIT )
{
total += num;
cin >> num;
count ++;
}
How about this design?
Correct answer, but extra input!
How to fix it?
average = total / count;
cout << "The average is " << average << "." << endl;
return 0;
}
AVERAGE of 10 numbers
const int LIMIT
= 10;
int main()
{
float num, total = 0, average;
int count;
cout << "Please input " << LIMIT << " numbers: " << endl;
cin >> num;
count = 0;
How about this design?
while ( count < LIMIT )
{
Correct!
total += num;
count ++;
Carefully check the final
if ( count != LIMIT )
cin >> num;
when designing loops!
}
average = total / count;
cout << "The average is " << average << "." << endl;
return 0;
}
status
More Arithmetic Operators
validCount ++;
// validCount = validCount + 1;
totalCount --;
// totalCount = totalCount - 1;
total += score;
// total = total + score;
total -= score;
// total = total - score;
yValue /= xValue;
// yValue = yValue / xValue;
yValue %= xValue;
// yValue = yValue % xValue;
yValue *= xValue;
// yValue = yValue * xValue;
Exercise
 int num = 5, result = 10;
What is the value of result?
 result /= num;
 result *= num – 3;
 result -= result % num;
 result %= 3 * 2;
2
20
10
4
AVERAGE of 10 numbers
const int LIMIT
= 10;
int main()
{
float num, total = 0, average;
int count = LIMIT;
cout << "Please input " << LIMIT << " numbers: " << endl;
while ( count > 0 )
{
cin >> num;
count --;
total += num;
}
average = total / LIMIT;
cout << "The average is " << average << "." << endl;
return 0;
}
Count-controlled loop
 Two ways:
 increase a counter till reaching the up-limit
 decrease a counter till reaching the bottom-limit
 Which one to choose depends on the problem and
your design.
Three Types of Loops
 Sentinel-controlled loop
 the loop stops when LCV become certain value.
while ( LCV != END_VALUE )
 Count-controlled loop
 the loop executes LIMIT times.
while ( count <= LIMIT )
 End-of-file-controlled loop
 the loops stops when reaching the end of the input file.
while ( !cin.eof() )
Loading an Input File in HiC
 Click the RUN menu
 Select option "Set Input File …"
 Click “Load Input”
 Browse to the file and open it
 Select the Input (Interactive) radio button
 Click OK
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Function cin.eof()
 returns true (end of file) or false
 eof():
end of file
OR end of input
 From keyboard: [CTRL-D] to indicate eof.
 From File:
 Not True after reading the last item in the file
 True when trying to read after reading the last item in the file
 while ( ! cin.eof() ) is the same as while ( cin )
Example of cin.eof()
int theInput;
int count = 0;
cout << "What is your input: ";
cin >> theInput;
while (!cin.eof())
{
count ++;
cout << "What is your input: ";
cin >> theInput;
}
cout << endl << "Last input: " << theInput;
cout << endl << "Count: " << count;
What is the output if input 1\n2\n3\n4[ctrl-d]?
What is the output if input 1\n2\n3\n4\n[ctrl-d]?
What is the output if input 50\n55.5\n60?
How to design loops
 What is the condition that ends the loop?
 How should the condition be initialized?
 How should the condition be updated?
 What is the process being repeated?
 What variables do we need to store the information?
 How should the process be initialized?
 How should the process be updated?
 What is the state of the program on exiting the loop?
Example: Find the nth Fibonacci number
 Fibonacci number: 0,1,1,2,3,5,8,13,…
Pseudo Code
previous = 0
current = 1
count = 1
While count is not n yet
fibonacci = current + previous
previous = current
current = fibonacci
increase count by 1
print fibonacci
Keep track of a previous value is
sometimes important!
int previous, current, fibonacci;
int count, limit;
cout <<
<<
<<
cin >>
"Please input the index of “
"the fibonacci number “
(starting with 0): ";
limit;
previous = 0;
current = 1;
count = 1;
while ( count < limit )
{
fibonacci = current + previous;
previous = current;
current = fibonacci;
count ++;
}
cout << "The " << limit
<< "th fibonacci number is "
<< fibonacci << "." << endl;
Nested Loop: table calculation
 print 30 numbers as a 5*6 table:
10
11
12
13
14
15
20
22
24
26
28
30
30
33
36
39
42
45
40
44
48
52
56
60
50
55
60
65
70
75
Pseudo Code
While row is not 5 yet
first cell = row * 10
print cell
while column is not 6 yet
current cell = previous cell + #row
print cell
column ++
row++
Nested Loop: table calculation
const int ROW_LIMIT
= 5;
const int COLUMN_LIMIT = 6;
int main()
{
int rowCount = 1, columnCount;
int cellValue;
What if rowCount and columnCount
are initialized as 0?
while ( rowCount <= ROW_LIMIT )
{
columnCount = 1;
cellValue = rowCount * 10;
cout << endl << cellValue;
columnCount ++;
while ( columnCount <= COLUMN_LIMIT )
{
cellValue = cellValue + rowCount;
cout << "
" << cellValue;
columnCount ++;
}
rowCount ++;
}
return 0;
}
Nested Loop Example: print a pyramid
 print a pyramid using $ sign.
Pseudo Code
height = HEIGHT
While height is not 0 yet
print (height-1) spaces
print (2*(HEIGHT-height)+1 )$
decrease height by 1
$
$$$
$$$$$
$$$$$$$
$$$$$$$$$
$$$$$$$$$$$
Nested Loop Example: print a pyramid
const int HEIGHT = 10;
string spaceLine;
string dollarLine;
int height = HEIGHT;
int count;
while ( height > 0 )
{
spaceLine = "";
dollarLine = "";
count = 0;
while ( count < height - 1 )
{
spaceLine += " ";
count ++;
}
count = 0;
while ( count < 2 * ( HEIGHT - height ) + 1 )
{
dollarLine += "$";
count ++;
}
cout << spaceLine << dollarLine << endl;
height --;
}
Trace in HiC
Window/Console
View/Status Window
Break Point
Step Over
Run/Watch
Reset
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Trace Execution
Range unknown
int score, max, count;
count = 0;
cin >> score;
while (score != -1)
{
count ++;
if (count == 1)
max = score;
else
{
if (score > max)
max = score;
}
cin >> score;
}
if (count == 0)
cout << “No scores!”;
else
cout << “The maximal score is ” << max;
Input Scores:
45 55 39 -1
score ?
45
55
39 -1
?
max
55
45
1
2
3
count ? 0
Tracing
Range Known
const int LOW_LIMIT = 0;
const int HIGH_LIMIT = 60;
int score, max = LOW_LIMIT;
cin >> score;
while (score != -1)
{
if (score < LOW_LIMIT ||
score > HIGH_LIMIT)
cout << “Invalid score: ”
<< score;
else
{
if (score > max)
max = score;
}
cin >> score;
}
Tracing
Input: 48
score
?
48
54
66
53
59
max
0
48
54
54
66
53
59
59
-1
How to do it?
•
One statement each line
•
Do not cross old values
•
Blank when no new value
WILL BE ON QUIZ
And Test 1
And Final!
-1
Tracing Nested Loops
int xValue, yValue, zValue;
xValue = 3;
while (xValue > 1)
{
zValue = 1;
yValue = xValue;
while (yValue > 0)
{
zValue *= yValue;
yValue --;
}
xValue
?
3
yValue
?
zValue
?
1
3
3
2
6
1
6
0
2
1
cout << "What is this: " <<
zValue;
2
2
1
xValue --;
2
}
0
1
Tracing exercise
int previous, current, fibonacci;
int count, limit;
cout <<
<<
<<
cin >>
"Please input the index of “
"the fibonacci number “
(starting with 0): ";
limit;
previous = 0;
current = 1;
count = 1;
while ( count < limit )
{
fibonacci = current + previous;
previous = current;
current = fibonacci;
count ++;
}
cout << "The " << limit
<< "th fibonacci number is "
<< fibonacci << "." << endl;
Input: 5 (limit)
previous current Fibonacci count
More on formatting output
 #include <iostream>
 showpoint
 #include <iomanip>
 setprecision()
 setw()
 fixed
 left
 right
showpoint: show the decimal point
 showpoint is a flag set to always show the decimal point for
float values inserted into the stream.
 The flag can be unset using noshowpoint manipulator.
 Need to include <iostream>
#include <iostream>
using namespace std;
int main ()
{
double a, b, pi;
a=30;
b=10000;
pi=3.14156;
The output is:
30.0000 10000.0 3.14156
30
10000
3.14156
tab
cout <<
showpoint << a << '\t' << b << '\t' << pi << endl;
cout << noshowpoint << a << '\t' << b << '\t' << pi << endl;
return 0;
}
setprecision(n)
 n determines the maximum number of digits that shall be output
 The flag fixed fixes the number of decimal places to n.
 Need to include <iomanip>
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
double num1 = 0.12345678;
int num2
= 1;
cout
cout
cout
cout
<<
<<
<<
<<
num1 << endl;
setprecision(2) << num1 << endl;
setprecision(4) << num1 << endl;
num1 << endl;
cout << fixed << num2 << endl;
cout << float(num2) << endl;
return 0;
}
The output is:
0.123457
0.12
0.1235
0.1235
1
1.0000
setw(n): set field width
 n determines the minimum number of characters written in the
output. If the natural length is shorter than n, it will fill with spaces.
 flag left and right determine the position of the output in the field;
if not specified, the default is right.
 Need to include <iomanip>
The output is:
#include <iostream>
#include <iomanip>
using namespace std;
int main ()
{
cout << setw(5);
cout << 77 << setw(5) << 66 << 55 << endl;
cout << left << setw (5);
cout << 77 << setw(5) << 66 << 55 << endl;
cout << setw(5) << right << 1.23 << endl;
return 0;
}
77
6655
77
66
55
1.23
Unlike setprecision(n),
setw(n) only affects the
next output field!
Summary
 Four parts of a loop: initialize, test, loop body, update LCV
 three types of loop
 sentinel-controlled loop
 count-controlled loop
 eof-controlled loop
 nested loop
 trace your execution
 manipulate your output
 showpoint
 setprecision(n)
 setw(n)
Style
Your submission as of the above date using HiC, v3.1.8. If this is a
programming assignment, please review the assignment writeup and programming
ground rules to make sure you didn't miss anything.
File: J:\CS143\Programs\Program 1\prog1.cpp:
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#include <iostream>
#include <string>
using namespace std;
int main()
{
...
Miss Comment Block!
Could lose 3 points!
Style
Your submission as of the above date using HiC, v3.1.8. If this is a
programming assignment, please review the assignment writeup and programming
ground rules to make sure you didn't miss anything.
File: J:\CS143\Programs\Program 1\prog1.cpp:
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//--------------------------------------------------------------------// Name:
John Smith
//
// Course: CS 143, Section 3, Fall 2011
//
// Purpose: This program converts between kilometers and
//
miles or between Fahrenheit temperature and Celsius.
//
// Input : This program accepts the following prompted input
//
from the keyboard:
//
// Output: This program provides the following output prompts to
//
standard output (the monitor):
//
"Input a type: kilometers, miles, fahrenheit, or celsius;
//
followed by a space and then an amount: "
//--------------------------------------------------------------------#include <iostream>
#include <string>
using namespace std;
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Style
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int main()
{
const float KM_PER_MILE
const float FREEZING_F
const float FAHR_PER_CELSIUS
string units;
float amount, conversion;
= 1.61;
= 32.0;
= 9.0 / 5.0;
cout << "Input a type: kilometers, miles, fahrenheit, or celsius;"
<< endl << "followed by a space and then an amount: " << endl;
cin >> units >> amount;
Constants should be before main()
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const float KM_PER_MILE
const float FREEZING_F
const float FAHR_PER_CELSIUS
= 1.61;
= 32.0;
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
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Style
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const float KM_PER_MILE
const float FREEZING_F
const float FAHR_PER_CELSIUS
= 1.61;
= 32.0;
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
cout << "Input a type: kilometers, miles, fahrenheit, or celsius;"
<< endl << "followed by a space and then an amount: " << endl;
cin >> units >> amount;
Do not indent constants!
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const float KM_PER_MILE
const float FREEZING_F
const float FAHR_PER_CELSIUS
= 1.61;
= 32.0;
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
cout << "Input a type: kilometers, miles, fahrenheit, or celsius;"
<< endl << "followed by a space and then an amount: " << endl;
cin >> units >> amount;
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Style
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if (amount > 120)
{
conversion = (amount – 32.0) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
Magic Number!
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
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Style
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
Brace Alignment!
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
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Style
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if (amount > MAX_FAHR_TEMP)
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{
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conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
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cout << endl << "Temperature " << amount << " degrees in “
<< "Fahrenheit is " << conversion << " degrees in Celsius.";
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}
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else
Line too long!
Each line can have at most 74 columns!
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
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Style
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in “
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
Alignment!
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
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Style
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in “
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
cout << “Invalid unit!!”;
Indentation!
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if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
cout << “Invalid unit!!”;
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Style
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81:
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83:
84:
if (amount > MAX_FAHR_TEMP)
{cout << “Invalid unit!!”;}
else
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << “The result is good.";
}
Braces on separate lines!
76:
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81:
82:
83:
84:
if (amount > MAX_FAHR_TEMP)
{
cout << “Invalid unit!!”;
}
else
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
cout << “The result is good.";
}
51
Style
76:
77:
78:
79:
80:
81:
82:
83:
if (amount>MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F)/FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount<<" degrees in “
<< "Fahrenheit is "<<conversion
<< " degrees in Celsius.";
}
else
Space before and after operator!
76:
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78:
79:
80:
81:
82:
83:
if ( amount > MAX_FAHR_TEMP )
{
conversion = ( amount - FREEZING_F ) / FAHR_PER_CELSIUS;
cout << endl << "Temperature " << amount << " degrees in "
<< "Fahrenheit is " << conversion
<< " degrees in Celsius.";
}
else
52
Style
76:
77:
78:
82:
83:
84:
85:
86:
87:
88:
89:
90:
91:
92:
93:
94:
if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
}
else if
{
}
else
{
No blank line before/after else!
76:
77:
78:
79:
80:
81:
82:
83:
84:
85:
86:
if (amount > MAX_FAHR_TEMP)
{
conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS;
. . .
}
else if
{
. . .
}
else
{
53
Style
33:
34:
35:
36:
37:
38:
39:
40:
41:
42:
43:
44:
const float FAHR_PER_CELSIUS
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
cout << "Input a type: kilometers, miles, fahrenheit, or celsius;"
<< endl << "followed by a space and then an amount: " << endl;
cin >> units >> amount;
No blank line before/after brace!
32:
36:
37:
38:
39:
40:
41:
42:
43:
44:
const float FAHR_PER_CELSIUS
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
cout << "Input a type: kilometers, miles, fahrenheit, or celsius;"
<< endl << "followed by a space and then an amount: " << endl;
cin >> units >> amount;
54
Style
35:
36:
37:
38:
39:
40:
41:
const float Fahr_Per_Celsius
= 9.0 / 5.0;
int main()
{
string variable;
float amount, conversion;
Naming conversion!
35:
36:
37:
38:
39:
40:
41:
42:
43:
44:
const float FAHR_PER_CELSIUS
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
cout << "Input a type: kilometers, miles, fahrenheit, or celsius;"
<< endl << "followed by a space and then an amount: " << endl;
cin >> units >> amount;
55
Style
35:
36:
37:
38:
39:
40:
41:
42:
const float FAHR_PER_CELSIUS
= 9.0 / 5.0;
int main()
{
string unit;
string kilo = “kilometers”;
float amount, conversion;
Unused code!
35:
36:
37:
38:
39:
40:
41:
42:
43:
44:
45:
const float FAHR_PER_CELSIUS
= 9.0 / 5.0;
int main()
{
string units;
float amount, conversion;
. . .
cin >> units >> amount;
if ( unit == “kilometers” )
{
. . .
56