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1、College of Information Science and Engineering,Wuhan University of Science and Technology第六章 循環(huán)控制概述C語言可實現(xiàn)循環(huán)的語句：用goto 和 if 構成循環(huán)while 語句do while 語句for 語句循環(huán)的嵌套(難點)1College of Information Science and Engineering,Wuhan University of Science and Technologygotov功能：無條件轉(zhuǎn)移語句v說明：l不能用整數(shù)作標號l只能出現(xiàn)在goto所在函數(shù)內(nèi),且唯一l只能

2、加在可執(zhí)行語句前面l限制使用goto語句goto語句及用goto構成循環(huán)goto語句一般格式：goto 語句標號；.標號：語句；2College of Information Science and Engineering,Wuhan University of Science and Technology例 用if 和goto語句構成循環(huán)，求/*ch6_1_1.c*/#include main()int i,sum=0;i=1;loop:if(i=100)sum+=i;i+;goto loop;printf(%d,sum);sum=0+1sum=1+2=3sum=3+3=6sum=6+4su

3、m=4950+100=5050循環(huán)初值循環(huán)初值循環(huán)終值循環(huán)終值循環(huán)變量增值循環(huán)變量增值循環(huán)條件循環(huán)條件循環(huán)體循環(huán)體p1133College of Information Science and Engineering,Wuhan University of Science and Technology/*ch6_1.c*/#include main()int number,sum=0;read_loop:scanf(%d,&number);if(!number)goto print_sum;sum+=number;goto read_loop;print_sum:printf(The tota

4、l sum is%dn,sum);例 從鍵盤輸入一組數(shù)據(jù)，以0結(jié)束輸入，求數(shù)據(jù)和4College of Information Science and Engineering,Wuhan University of Science and Technologywhile語句v一般形式：while(表達式)循環(huán)體語句；v執(zhí)行流程：expr循環(huán)體循環(huán)體假假(0)真真(非非0)while5College of Information Science and Engineering,Wuhan University of Science and Technologyv特點：先判斷表達式，后執(zhí)行循環(huán)體v

5、說明：l循環(huán)體有可能一次也不執(zhí)行l(wèi)循環(huán)體可為任意類型語句l下列情況，退出while循環(huán)u條件表達式不成立（為零）u循環(huán)體內(nèi)遇break,return,gotol無限循環(huán):while(1)循環(huán)體;while語句語句6College of Information Science and Engineering,Wuhan University of Science and Technology例例 用用while循環(huán)求循環(huán)求：/*ch6_2.c*/#include main()int i,sum=0;i=1;while(i=100)sum=sum+i;i+;printf(%d,sum);循環(huán)初值循

6、環(huán)終值循環(huán)變量增值循環(huán)條件循環(huán)體p1147College of Information Science and Engineering,Wuhan University of Science and Technology例：在屏幕上輸出110的平方/*ch6_3.c*/#include main()int i=1;while(i=10)printf(%d*%d=%dn,i,i,i*i);i+;運行結(jié)果：1*1=12*2=43*3=94*4=165*5=256*6=367*7=498*8=649*9=8110*10=100注意：循環(huán)體如果有多條語句,應用花括號括起來!8College of In

7、formation Science and Engineering,Wuhan University of Science and Technologydowhile語句v一般形式：do 循環(huán)體語句；while(表達式);v執(zhí)行流程：do循環(huán)體循環(huán)體expr假假(0)真真(非非0)while9College of Information Science and Engineering,Wuhan University of Science and Technologyv特點：先執(zhí)行循環(huán)體，后判斷表達式v說明：l至少執(zhí)行一次循環(huán)體ldowhile可轉(zhuǎn)化成while結(jié)構expr循環(huán)體循環(huán)體假假(0

8、)真真(非非0)循環(huán)體循環(huán)體While循環(huán)循環(huán)10College of Information Science and Engineering,Wuhan University of Science and Technology例 用dowhile循環(huán)求/*ch6_4.c*/#include main()int i,sum=0;i=1;do sum+=i;i+;while(i=100);printf(%d,sum);11College of Information Science and Engineering,Wuhan University of Science and Technolog

9、y例 while和dowhile比較/*ch6_5.c*/#include main()int i,sum=0;scanf(%d,&i);do sum+=i;i+;while(i=10);printf(%d,sum);main()int i,sum=0;scanf(%d,&i);while(i=10)sum+=i;i+;printf(%d,sum);12College of Information Science and Engineering,Wuhan University of Science and Technologyfor語句v一般形式：for(expr1;expr2;expr3)

10、循環(huán)體語句；v執(zhí)行流程：expr2循環(huán)體循環(huán)體假假(0)真真(非非0)forexpr1expr313College of Information Science and Engineering,Wuhan University of Science and Technologyvfor語句一般應用形式：for(循環(huán)變量賦初值；循環(huán)條件；循環(huán)變量增值)循環(huán)體語句；例 用for循環(huán)求#include main()int i,sum=0;for(i=1;i=100;i+)sum+=i;printf(%d,sum);14College of Information Science and Engine

11、ering,Wuhan University of Science and Technologyv說明：lfor語句中expr1,expr2,expr3 類型任意，都可省略，但分號；不可省l無限循環(huán):for(;)lfor語句可以轉(zhuǎn)換成while結(jié)構expr1;while(expr2)循環(huán)體語句；expr3;15College of Information Science and Engineering,Wuhan University of Science and Technology例：#include main()int i=0;for(i=0;i10;i+)putchar(a+i);運行

12、結(jié)果：abcdefghij#includemain()int i=0;for(;i10;i+)putchar(a+i);#includemain()int i=0;for(;i10;)putchar(a+(i+);#includemain()int i=0;for(;i10;putchar(a+i),i+);16College of Information Science and Engineering,Wuhan University of Science and Technology例:p1201.for(i=0,j=100;i=j;i+,j-)2.k=i+j;2.for(i=0;(c=g

13、etchar()!=n;i+=c);3.for(;(c=getchar()!=n;)printf(“%c”,c);逗號表達式,包含兩個賦值表達式p129 習題6.2可以借鑒17College of Information Science and Engineering,Wuhan University of Science and Technology循環(huán)的嵌套v三種循環(huán)可互相嵌套,層數(shù)不限v外層循環(huán)可包含兩個以上內(nèi)循環(huán),但不能相互交叉v嵌套循環(huán)的執(zhí)行流程嵌套循環(huán)的跳轉(zhuǎn)，禁止：從外層跳入內(nèi)層跳入同層的另一循環(huán)向上跳轉(zhuǎn)18College of Information Science and En

14、gineering,Wuhan University of Science and Technology(1)while()while().(2)do do while();.while();(3)while()do while();.(4)for(;)do while();while().19College of Information Science and Engineering,Wuhan University of Science and Technology例 循環(huán)嵌套，輸出九九乘法表1234567891234567892468101214161836912151821242791

15、827364554637281.ij20College of Information Science and Engineering,Wuhan University of Science and Technology/*ch6_6.c*/#include main()int i,j;for(i=1;i10;i+)printf(%4d,i);printf(n-n);for(i=1;i10;i+)for(j=1;j10;j+)printf(j=9)?%4dn:%4d,i*j);例 循環(huán)嵌套，輸出九九乘法表21i10printf假假(0)真真(非非0)i=1j+j=1j10真真(非非0)假假(0)

16、i+for(i=1;i10;i+)for(j=1;j10;j+)printf(j=9)?%4dn:%4d,i*j);外循環(huán)內(nèi)循環(huán)循環(huán)嵌套22College of Information Science and Engineering,Wuhan University of Science and Technology功能：在循環(huán)語句和switch語句中,終止并跳出循環(huán)體或開關體說明：break只能終止并跳出最近一層的結(jié)構break不能用于循環(huán)語句和switch語句之外的任何其它語句之中輔助控制語句break語句23College of Information Science and Engin

17、eering,Wuhan University of Science and Technologyexprbreak;假假(0)真真(非非0)whiledobreak;.expr假假(0)真真(非非0)while24College of Information Science and Engineering,Wuhan University of Science and Technologyexpr2break;.假(0)真(非0)forexpr1expr3switchexpr語句組語句組1break;語句組語句組2break;語句組語句組nbreak;語句組語句組break;.const 1

18、const 2const ndefaultcase 25College of Information Science and Engineering,Wuhan University of Science and Technology例 break舉例：輸出圓面積，面積大于100時停止/*ch6_7.c*/#define PI 3.14159main()int r;float area;for(r=1;r100)break;printf(r=%d,area=%.2fn,r,area);26College of Information Science and Engineering,Wuhan

19、University of Science and Technology例：小寫字母轉(zhuǎn)換成大寫字母,直至輸入非小寫字母字符#include main()int i,j;char c;while(1)c=getchar();if(c=a&c=z)putchar(c-a+A);else break;27continue語句v功能：結(jié)束本次循環(huán)，跳過循環(huán)體中尚未執(zhí)行的語句，進行下一次是否執(zhí)行循環(huán)體的判斷v僅用于循環(huán)語句中exprcontinue;假假(0)真真(非非0)while真真(非非0)docontinue;.expr假假(0)whileexpr2continue;.假假(0)真真(非非0)f

20、orexpr1expr328College of Information Science and Engineering,Wuhan University of Science and Technology例 求輸入的十個整數(shù)中正數(shù)的個數(shù)及其平均值#include/*ch6_10.c*/main()int i,num=0,a;float sum=0;for(i=0;i10;i+)scanf(%d,&a);if(a=0)continue;num+;sum+=a;printf(%d plus integers sum:%6.0fn,num,sum);printf(Mean value:%6.2fn

21、,sum/num);29College of Information Science and Engineering,Wuhan University of Science and Technology程序舉例 p124t=1,pi=0,n=1.0,s=1當|t|1e-6pi=pi+tn=n+2s=-st=s/npi=pi*4輸出pi分子：分子：1，-1，1，-1分母：分母：1，3，5，7，.30College of Information Science and Engineering,Wuhan University of Science and Technology例 求Fibonacc

22、i數(shù)列：1，1，2，3，5，8，的前40個數(shù)f1=1,f2=1for i=1 to 20輸出f1,f2f1=f1+f2f2=f2+f11534233159710946750255142293524578241578171855377258417711121393832040570288739088169213896104181286571964181346269922746563245986321144987676546368317811217830914930352102334155p12531College of Information Science and Engineering,Wu

23、han University of Science and Technology例 判斷m是否素數(shù) p126讀入mk=mi=2當ikm被i整除真假用break結(jié)束循環(huán)i=i+1ik+1真假輸出:m”是素數(shù)”輸出:m”不是素數(shù)”在此基礎上，試編程輸出100200 之間的全部素數(shù)。32College of Information Science and Engineering,Wuhan University of Science and Technology例 譯密碼 p128例如 Hello,world!譯成密碼：Lipps,asvph!26個字母按順序構成封閉的環(huán)狀,將任意一字母變成其后的第

24、4個字母.非字母字符不變33College of Information Science and Engineering,Wuhan University of Science and Technology#includemain()char c;while(c=getchar()!=n)if(c=a&c=A&cZ&cz)c=c-26;printf(“%c”,c);例 譯密碼34College of Information Science and Engineering,Wuhan University of Science and Technology課堂練習：1、int k=10;whil

25、e(k=0)k=k-1;2、int k=10;while(k=0)k-;3、while(!E);中表達式!E等價于什么？4、for(i=1;i+4;);執(zhí)行后i=?執(zhí)行結(jié)束后k=?35College of Information Science and Engineering,Wuhan University of Science and Technology雞兔共有30只，腳共有90只，以下程序求各有多少雞和兔。請?zhí)羁铡or(x=1;x=29;x+)y=30-x;if()printf(“%d,%dn”,x,y);36College of Information Science and Engineering,Wuhan University of Science and Technology作業(yè):用循環(huán)程序完成下列各題p1296.2、6.3、6.6總結(jié)：本章主要介紹循環(huán)控制用到的語句和方法while，do while，for另外還有起輔助作用的break,continue語句難點：盡快熟悉循環(huán)控制程序的基本技巧！多動手練習！37