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Chapter 5 迴圈

Chapter 5 迴圈. 迴圈每次的增量，若增量為 1 ，則可省略. 變數 I 的終止數值 N. I=1→2→3→…→N 迴圈共跑 N 次. 設定變數 I 的初值 1. 指定一個行代碼，兩行代碼間的程式會變成一個迴圈. 5-1 Do. 程式說明 do 10, I = 1, N, 1 … 10 continue. 迴圈每次的增量 2. 變數 I 的終止數值 N. I=2→4→6→…→N 迴圈共跑 N/2 次. 設定變數 I 的初值 2. 也可以用 do - end do 當作一個迴圈. 5-1 Do. 程式說明 do I = 2, N, 2 …

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Chapter 5 迴圈

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  1. Chapter 5 迴圈

  2. 迴圈每次的增量，若增量為1，則可省略 變數I的終止數值N I=1→2→3→…→N迴圈共跑N次 設定變數I的初值1 指定一個行代碼，兩行代碼間的程式會變成一個迴圈 5-1 Do 程式說明 do 10, I = 1, N, 1 … 10 continue

  3. 迴圈每次的增量2 變數I的終止數值N I=2→4→6→…→N迴圈共跑N/2次 設定變數I的初值2 也可以用do - end do當作一個迴圈 5-1 Do 程式說明 do I = 2, N, 2 … end do

  4. < Ex. 完整程式> program ex0501 implicit none integer :: I integer, parameter :: N=10 do 10 I = 1, N, 1 write(*,*) 'Do - Loop Demo' 10 continue stop end program ex0501 < Ex. 執行結果> Do - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop DemoDo - Loop Demo 5-1 Do Do使用時機 連續重複執行某一段程式碼

  5. 當判別式為真時，執行迴圈當判別式為假時，跳出迴圈當判別式為真時，執行迴圈當判別式為假時，跳出迴圈 do while - end do之間為一個迴圈 5-2 Do while 程式說明 do while (logical_expr) … end do

  6. 應改成i==4 5-2 Do while 永久迴圈 當判別式永遠成真時，會形成永久迴圈 • do while (1) • i=5do while(i>4) i=i+1end do • i=4do while(i=4) i=i+1end do

  7. .FALSE. logical_expr判斷式 .TRUE. statement 1statement 2… 5-2 Do while 程式流程圖

  8. < Ex. 完整程式> program ex0502 implicit none integer, parameter :: answer=45 integer :: input = 0 do while(input /= answer) write(*,*) 'answer =' read(*,*) input end do write(*,*) 'You are right!' stop end program ex0502 < Ex. 執行結果> answer=10 <輸入 1 0 [ENTER] > answer=45 <輸入 4 5 [ENTER] > You are right! 5-2 Do while Do while使用時機 不能事先預知 會執行幾次的迴圈時

  9. < Ex. 完整程式> program ex0503 implicit none integer :: i integer, parameter :: n=10 do i = 1, n if (i == 4) cycle write(*, '(I3)') i end do stop end program ex0503 當i=4時，不會被印出來而繼續執行迴圈 1235678910 < Ex. 執行結果> 5-3 Cycle Cycle使用時機 略過迴圈中之後的敘述，直接 跳回迴圈的開頭來執行迴圈

  10. < Ex. 完整程式> program ex0504 implicit none integer, parameter :: answer=45 integer :: input do while (.true.) write(*,*) "answer =" read(*,*) input if (input == answer) exit end do write(*,*) "You are right!" stop end program ex0504 永久迴圈 < Ex. 執行結果> answer=10 <輸入 1 0 [ENTER] > answer=45 <輸入 4 5 [ENTER] > You are right! 等式input=answer成立則跳離此迴圈 5-4 Exit Exit使用時機 直接跳出一個在運作中的迴圈

  11. < Ex. 完整程式> program ex0506 implicit none integer :: i, j loop1: do i = 1,3 loop2: do j = 1,3 if(j == 2) cycleloop2 if(i == 2) exit loop1 write(*,'(t2,A1,I3,A1,I3,A1)') '(',i,',',j,')' end do loop2 end do loop1 stop end program ex0506 跳到loop2迴圈的起頭執行程式 跳出整個loop1迴圈(也會同時跳出loop2迴圈) < Ex. 執行結果> ( 1, 1)( 1, 3) 5-5 具名的迴圈

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