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Chapter 6

Chapter 6. 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;

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Chapter 6

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  1. Chapter 6 Looping

  2. 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; cout << “The max value is ” << max << endl; max = num1; if ( num2 > max ) max = num2; if ( num3 > max ) max = num3; How about finding the MAX of n number?

  3. Example: MAX of n numbers int num, max; cin >> num; • max = num; while ( num != -1 ) { if ( num > max ) max = num; cin >> num; } cout << “The max value is ” << max << endl; return 0; • 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? if ( num == -1 ) { cout << “No input!”; return 0; }

  4. 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; }

  5. 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; }

  6. While Loop Initialization (LCV and others) while (LogicalExpression) (Testing LCV) false true Do Work Update LCV Statement after loop

  7. 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. { }

  8. 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?

  9. 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?

  10. 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))

  11. 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;

  12. 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() )

  13. 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

  14. 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; // total = total + num; count ++; // count = count + 1; } average = total / count; cout << "The average is " << average << "." << endl; return 0; }

  15. 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 ++; } average = total / count; cout << "The average is " << average << "." << endl; return 0; } How about this design? Wrong! sum 9 numbers / 10 How to fix it?

  16. 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 ++; } average = total / count; cout << "The average is " << average << "." << endl; return 0; } How about this design? Correct answer, but extra input! How to fix it?

  17. 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; count ++; if ( count != LIMIT ) cin >> num; } average = total / count; cout << "The average is " << average << "." << endl; return 0; } How about this design? Correct! Carefully check the final status when designing loops!

  18. 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;

  19. 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

  20. 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; }

  21. 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.

  22. 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() )

  23. 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

  24. 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 )

  25. 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?

  26. 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?

  27. 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 int previous, current, fibonacci; int count, limit; cout << "Please input the index of “ << "the fibonacci number “ << (starting with 0): "; cin >> limit; previous = 0; current = 1; count = 1; while ( count < limit ) { fibonacci = current + previous; previous = current; current = fibonacci; count ++; } cout << "The " << limit << "thfibonacci number is " << fibonacci << "." << endl; Keep track of a previous value is sometimes important!

  28. Nested Loop: table calculation • print 30 numbers as a 5*6 table: 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++

  29. Nested Loop: table calculation const int ROW_LIMIT = 5; const int COLUMN_LIMIT = 6; int main() { int rowCount = 1, columnCount; int cellValue; 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; } What if rowCount and columnCount are initialized as 0?

  30. 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 $ $$$ $$$$$ $$$$$$$ $$$$$$$$$ $$$$$$$$$$$

  31. 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 --; }

  32. Trace in HiC Window/Console View/Status Window Break Point Step Over Run/Watch Reset

  33. 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 max count 45 55 39 -1 ? 55 45 ? 0 1 2 3

  34. Tracing • Tracing • Input: 48 54 66 53 59 -1 • score max • ? 0 • 48 • 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! 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; }

  35. Tracing Nested Loops int xValue, yValue, zValue; xValue = 3; while (xValue > 1) { zValue = 1; yValue = xValue; while (yValue > 0) { zValue *= yValue; yValue --; } cout << "What is this: " << zValue; xValue --; } xValueyValuezValue ? ? ? 3 1 3 3 2 6 1 6 0 2 1 2 2 1 2 0 1

  36. Tracing exercise int previous, current, fibonacci; int count, limit; cout << "Please input the index of “ << "the fibonacci number “ << (starting with 0): "; cin >> limit; previous = 0; current = 1; count = 1; while ( count < limit ) { fibonacci = current + previous; previous = current; current = fibonacci; count ++; } cout << "The " << limit << "thfibonacci number is " << fibonacci << "." << endl; Input: 5 (limit) previous current Fibonacci count

  37. More on formatting output • #include <iostream> • showpoint • #include <iomanip> • setprecision() • setw() • fixed • left • right

  38. 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; cout << showpoint<< a << '\t' << b << '\t' << pi << endl; cout << noshowpoint<< a << '\t' << b << '\t' << pi << endl; return 0; } The output is: 30.0000 10000.0 3.14156 30 10000 3.14156 tab

  39. setprecision(n) • ndetermines 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 << num1 << endl; cout << setprecision(2) << num1 << endl; cout << setprecision(4) << num1 << endl; cout << 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

  40. 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: 77 6655 77 66 55 1.23 #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; } Unlike setprecision(n), setw(n) only affects the next output field!

  41. 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)

  42. 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: 25: 26: #include <iostream> 27: #include <string> 28: using namespace std; 29: 30: int main() 31: { 32: ... Miss Comment Block! Could lose 3 points!

  43. 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: 1: //--------------------------------------------------------------------- 2: // Name: John Smith 3: // 4: // Course: CS 143, Section 3, Fall 2011 5: // 6: // Purpose: This program converts between kilometers and 7: // miles or between Fahrenheit temperature and Celsius. 8: // 9: // Input : This program accepts the following prompted input 10: // from the keyboard: 13: // 14: // Output: This program provides the following output prompts to 15: // standard output (the monitor): 16: // "Input a type: kilometers, miles, fahrenheit, or celsius; 17: // followed by a space and then an amount: " 24: //--------------------------------------------------------------------- 25: 26: #include <iostream> 27: #include <string> 28: using namespace std;

  44. Style 36: 37: int main() 38: { 30: const float KM_PER_MILE = 1.61; 31: const float FREEZING_F = 32.0; 32: const float FAHR_PER_CELSIUS = 9.0 / 5.0; 39: string units; 40: float amount, conversion; 41: 42: cout << "Input a type: kilometers, miles, fahrenheit, or celsius;" 43: << endl << "followed by a space and then an amount: " << endl; 44: cin >> units >> amount; Constants should be before main() 30: const float KM_PER_MILE = 1.61; 31: const float FREEZING_F = 32.0; 32: const float FAHR_PER_CELSIUS = 9.0 / 5.0; 36: 37: int main() 38: { 39: string units; 40: float amount, conversion; 41:

  45. Style 30: const float KM_PER_MILE = 1.61; 31: const float FREEZING_F = 32.0; 32: const float FAHR_PER_CELSIUS = 9.0 / 5.0; 36: 37: int main() 38: { 39: string units; 40: float amount, conversion; 41: 42: cout << "Input a type: kilometers, miles, fahrenheit, or celsius;" 43: << endl << "followed by a space and then an amount: " << endl; 44: cin >> units >> amount; Do not indent constants! 30: const float KM_PER_MILE = 1.61; 31: const float FREEZING_F = 32.0; 32: const float FAHR_PER_CELSIUS = 9.0 / 5.0; 36: 37: int main() 38: { 39: string units; 40: float amount, conversion; 41: 42: cout << "Input a type: kilometers, miles, fahrenheit, or celsius;" 43: << endl << "followed by a space and then an amount: " << endl; 44: cin >> units >> amount;

  46. Style 76: if (amount > 120) 77: { 78: conversion = (amount – 32.0) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else Magic Number! 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else

  47. Style 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else Brace Alignment! 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else

  48. Style 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in “ << "Fahrenheit is " << conversion << " degrees in Celsius."; 80: } 81: else Line too long! Each line can have at most 74 columns! 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else

  49. Style 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in “ 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else Alignment! 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else

  50. Style 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in “ 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else 84: cout << “Invalid unit!!”; Indentation! 76: if (amount > MAX_FAHR_TEMP) 77: { 78: conversion = (amount - FREEZING_F) / FAHR_PER_CELSIUS; 79: cout << endl << "Temperature " << amount << " degrees in " 80: << "Fahrenheit is " << conversion 81: << " degrees in Celsius."; 82: } 83: else 84: cout << “Invalid unit!!”;

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