Tài liệu Chapter 2 - Control Structures ppt

 2003 Prentice Hall, Inc. All rights reserved. 1 Chapter 2 - Control Structures Outline  Control Structures  if Selection Structure  if/else Selection Structure  while Repetition Structure  Formulating Algorithms: Case Study 1 (Counter-Controlled Repetition)  Formulating Algorithms with Top-Down, Stepwise Refinement: Case Study 2 (Sentinel-Controlled Repetition)  Formulating Algorithms with Top-Down, Stepwise Refinement: Case Study 3 (Nested Control Structures)  Assignment Operators  Increment and Decrement Operators  Essentials of Counter-Controlled Repetition  for Repetition Structure  switch Multiple-Selection Structure  do/while Repetition Structure  break and continue Statements  Logical Operators  Confusing Equality (==) and Assignment (=) Operators  Structured-Programming Summary  2003 Prentice Hall, Inc. All rights reserved. 2 Control Structures • Sequential execution – Statements executed in order • Transfer of control – Next statement executed not next one in sequence • 3 control structures (Bohm and Jacopini) – Sequence structure • Programs executed sequentially by default – Selection structures • if, if/else, switch – Repetition structures • while, do/while, for  2003 Prentice Hall, Inc. All rights reserved. 3 Control Structures • C++ keywords – Cannot be used as identifiers or variable names C++ Keywords Keywords common to the C and C++ programming languages auto break case char const continue default do double else enum extern float for goto if int long register return short signed sizeof static struct switch typedef union unsigned void volatile while C++ only keywords asm bool catch class const_cast delete dynamic_cast explicit false friend inline mutable namespace new operator private protected public reinterpret_cast static_cast template this throw true try typeid typename using virtual wchar_t  2003 Prentice Hall, Inc. All rights reserved. 4 if Selection Structure •inC++ If student’s grade is greater than or equal to 60 Print “Passed” if ( grade >= 60 ) cout << "Passed"; true false grade >= 60 print “Passed” A decision can be made on any expression. zero - false nonzero - true Example: 3 - 4 is true  2003 Prentice Hall, Inc. All rights reserved. 5 if/else Selection Structure • if – Performs action if condition true • if/else – Different actions if conditions true or false • Pseudocode if student’s grade is greater than or equal to 60 print “Passed” else print “Failed” • C++ code if ( grade >= 60 ) cout << "Passed"; else cout << "Failed";  2003 Prentice Hall, Inc. All rights reserved. 6 if/else Selection Structure • Ternary conditional operator (?:) – Three arguments (condition, value if true, value if false) • Code could be written: cout << ( grade >= 60 ? “Passed” : “Failed” ); truefalse print “Failed” print “Passed” grade >= 60 Condition Value if true Value if false  2003 Prentice Hall, Inc. All rights reserved. 7 Nested if/else structures •Example if ( grade >= 90 ) // 90 and above cout << "A"; else if ( grade >= 80 ) // 80-89 cout << "B"; else if ( grade >= 70 ) // 70-79 cout << "C"; else if ( grade >= 60 ) // 60-69 cout << "D"; else // less than 60 cout << "F";  2003 Prentice Hall, Inc. All rights reserved. 8 if/else Selection Structure • Compound statement – Set of statements within a pair of braces if ( grade >= 60 ) cout << "Passed.\n"; else { cout << "Failed.\n"; cout << "You must take this course again.\n"; } – Without braces, cout << "You must take this course again.\n"; always executed •Block – Set of statements within braces  2003 Prentice Hall, Inc. All rights reserved. 9 while Repetition Structure •Example int product = 2; while ( product <= 1000 ) product = 2 * product; product <= 1000 product = 2 * product true false  2003 Prentice Hall, Inc. All rights reserved. 10 Formulating Algorithms (Counter-Controlled Repetition) • Counter-controlled repetition – Loop repeated until counter reaches certain value • Definite repetition – Number of repetitions known •Example A class of ten students took a quiz. The grades (integers in the range 0 to 100) for this quiz are available to you. Determine the class average on the quiz. [...]... pass, pass, 2 2 2 2 2 2 2 2 2 2 = = = = = = = = = = fail): fail): fail): fail): fail): fail): fail): fail): fail): fail): 1 2 2 1 1 1 2 1 1 2 = = = = = = = = = = pass, pass, pass, pass, pass, pass, pass, pass, pass, pass, 2 2 2 2 2 2 2 2 2 2 = = = = = = = = = = fail): fail): fail): fail): fail): fail): fail): fail): fail): fail): 1 1 1 1 2 1 1 1 1 1  20 03 Prentice Hall, Inc All rights reserved 25 Assignment... int result; // one exam result 15 // process 10 students using counter-controlled loop 16 while ( studentCounter > result;  20 03 Prentice Hall, Inc All rights reserved 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 // if result 1, increment passes; if/else nested in while if... 6  20 03 Prentice Hall, Inc All rights reserved 30 Essentials of Counter-Controlled Repetition • Counter-controlled repetition requires – – – – Name of control variable/loop counter Initial value of control variable Condition to test for final value Increment/decrement to modify control variable when looping  20 03 Prentice Hall, Inc All rights reserved 1 // Fig 2. 16: fig 02_ 16.cpp 2 // Counter-controlled... while ( gradeCounter grade; // read grade from user 21 total = total + grade; // add grade to total 22 gradeCounter = gradeCounter + 1; // increment counter 23 }  20 03 Prentice Hall, Inc All rights reserved 24 25 26 27 28 29 // termination phase average = total / 10; // integer division // display result cout .  20 03 Prentice Hall, Inc. All rights reserved. 1 Chapter 2 - Control Structures Outline  Control Structures  if Selection Structure . Case Study 1 (Counter-Controlled Repetition)  Formulating Algorithms with Top-Down, Stepwise Refinement: Case Study 2 (Sentinel-Controlled Repetition) 