4.8 Thedo while Repetition Statement Thedo while repetition statement

Transcription

1 1 4.8 hedo while Repetition Statement hedo while repetition statement Similar to thewhile structure Condition for repetition tested after the body of the loop is performed All actions are performed at least once ormat: do { statement statement; } while ( condition ); condition false true 2 hedo while Repetition Example Example (lettingcounter = 1): do { printf( "%d ", counter ); } while (++counter <= 10); Prints the integers from1to10 1

2 fig04_09.c 3 1 /* ig. 4.9: fig04_09.c 2 Using the do/while repetition statement */ 3 #include <stdio.h> 4 5 /* function main begins program execution */ 6 int main() 7 { 8 int counter = 1; /* initialize counter */ 9 10 do { 11 printf( "%d ", counter ); /* display counter */ 12 } while ( ++counter <= 10 ); /* end do...while */ return 0; /* indicate program ended successfully */ } /* end function main */ Program Output hebreak andcontinue Statements break Causes immediate exit from awhile,for, do while or switch statement Program execution continues with the first statement after the structure Common uses of thebreak statement Escape early from a loop Skip the remainder of aswitch statement 2

3 1 /* ig. 4.11: fig04_11.c 2 Using the break statement in a for statement */ 3 #include <stdio.h> 4 5 /* function main begins program execution */ 6 int main() 7 { 8 int x; /* counter */ 9 10 /* loop 10 times */ 11 for ( x = 1; x <= 10; x++ ) { /* if x is 5, terminate loop */ 14 if ( x == 5 ) { 15 break; /* break loop only if x is 5 */ 16 } /* end if */ printf( "%d ", x ); /* display value of x */ 19 } /* end for */ printf( "\nbroke out of loop at x == %d\n", x ); return 0; /* indicate program ended successfully */ } /* end function main */ Broke out of loop at x == 5 fig04_11.c Program Output 5 6 continue hecontinue Statement Skips the remaining statements in the body of a while,for ordo while statement Proceeds with the next iteration of the loop while anddo while Loop-continuation test is evaluated immediately after thecontinue statement is executed for Increment expression is executed, then the loopcontinuation test is evaluated 3

4 1 /* ig. 4.12: fig04_12.c 2 Using the continue statement in a for statement */ 3 #include <stdio.h> 4 5 /* function main begins program execution */ 6 int main() 7 { 8 int x; /* counter */ 9 10 /* loop 10 times */ 11 for ( x = 1; x <= 10; x++ ) { /* if x is 5, continue with next iteration of loop */ 14 if ( x == 5 ) { 15 continue; /* skip remaining code in loop body */ 16 } /* end if */ printf( "%d ", x ); /* display value of x */ 19 } /* end for */ printf( "\nused continue to skip printing the value 5\n" ); return 0; /* indicate program ended successfully */ } /* end function main */ Used continue to skip printing the value 5 fig04_12.c Program Output 7 練 習 一 寫 一 個 C 語 言 程 式, 讓 使 用 者 輸 入 一 個 介 於 1 至 100 間 的 整 數 N 輸 出 1 至 N 間 ( 含 N) 所 有 不 為 3 或 5 倍 數 的 數 字 並 輸 出 這 樣 的 數 字 有 多 少 個 提 示 : 使 用 一 個 for 或 while 迴 圈 檢 查 1 至 N 間 的 所 有 整 數, 並 配 合 使 用 continue 敘 述 8 執 行 範 例 Input a number between 1 and 100: 16 1, 2, 4, 7, 8, 11, 13, 14, 16. otal 9 numbers. 4

5 4.10 Logical Operators 9 && ( logical AND ) Returnstrue if both conditions aretrue ( logical OR ) Returnstrue if either of its conditions aretrue! ( logical NO, logical negation ) Reverses the truth/falsity of its condition Unary operator, has one operand Useful as conditions in loops Expression true && false true false!false Result false true true he ruth able of && 10 expression1 expression2 expression1 && expression nonzero 0 nonzero 0 0 nonzero nonzero 1 5

6 he ruth able of 11 expression1 expression2 expression1 expression nonzero 1 nonzero 0 1 nonzero nonzero 1 he ruth able of! 12 expression! Expression 0 1 nonzero 0 6

7 Logical Operators Operators Associativity ype ! (type) right to left unary * / % left to right multiplicative + - left to right additive < <= > >= left to right relational ==!= left to right equality && left to right logical AND left to right logical OR?: right to left conditional = += -= *= /= %= right to left assignment, left to right comma 4.11 Confusing Equality (==) and Assignment (=) Operators Dangerous error Does not ordinarily cause syntax errors Any expression that produces a value can be used in control structures Nonzero values aretrue, zero values are false Example using==: if ( paycode == 4 ) printf( "You get a bonus!\n" ); 14 CheckspayCode, if it is4then a bonus is awarded 7

8 4.11 Confusing Equality (==) and Assignment (=) Operators Example, replacing== with=: 15 if ( paycode = 4 ) printf( "You get a bonus!\n" ); his setspaycode to4 4 is nonzero, so expression istrue, and bonus awarded no matter what thepaycode was Logic error, not a syntax error 16 lvalues L-values Expressions that can appear on the left side of an equation heir values can be changed, such as variable names x = 4; 8

9 17 rvalues R-values Expressions that can appear on the right side of an equation Constants, such as numbers Cannot write4 = x; Must writex = 4; lvalues can be used as rvalues, but not vice versa y = x; Structured-Programming Summary Se q u e n c e Sequence structure. 9

10 4.12 Structured-Programming Summary 19 Selection structure statement if statement (single selection) if else statement (double selection). switch (multiple selection) break break break 4.12 Structured-Programming Summary 20 Repetition structure while statement do while statement for statement 10

11 Structured Programming Structured programming Only single-entry/single-exit control structures are used Easier than unstructured programs to understand, test, debug and, modify programs 22 Rules for Structured Programming developed by programming community Rules: 1.Begin with the simplest flowchart 2.Stacking rule: Any rectangle (action) can be replaced by two rectangles (actions) in sequence 3.Nesting rule: Any rectangle (action) can be replaced by any control structure (sequence,if, if else,switch,while,do while or for) 4.Rules 2 and 3 can be applied in any order and multiple times 11

12 4.12 Structured-Programming Summary 23 Rule 1 - Begin with the simplest flowchart Rule 2 - Any rectangle can be replaced by two rectangles in sequence Rule 2 Rule 2 Rule Structured-Programming Summary 24 Rule 3 - Replace any rectangle with a control structure Rule 3 Rule 3 Rule 3 12

13 4.12 Structured-Programming Summary 25 Stacke d b uilding b lo cks Nested build ing blocks Overla pping b uilding blocks (Illega l in structured pro gra ms) 4.12 Structured-Programming Summary 26 igure 4.23 An unstructured flowchart. 13

14 Structured-Programming Summary All programs can be broken down into three controls Sequence handled automatically by compiler Selection if,if else orswitch Repetition while,do while orfor Can only be combined in two ways Nesting (rule 3) Stacking (rule 2) Any selection can be rewritten as anif statement, and any repetition can be rewritten as awhile statement 14