introduction to computing計(jì)算機(jī)概論課件b06-for再談分支語句

1、計(jì)算概論A課程 程序設(shè)計(jì)部分C 語言的基本成分 控制成分李戈北京大學(xué) 信息科學(xué)技術(shù)學(xué)院 軟件研究所計(jì)算機(jī)程序的基本結(jié)構(gòu)什么樣的結(jié)構(gòu)才能支持程序運(yùn)行的邏輯？1966年，G. Jacopini 和 C. Bohm在“Communications of the ACM”上發(fā)表論論文“Flow Diagrams, Turing Machines and Languages with Only Two Formation Rules” 。從理論上證明了：任何具有單入口單出口的程序都可以用三種基本結(jié)構(gòu)表達(dá)：順序結(jié)構(gòu)分支結(jié)構(gòu)循環(huán)結(jié)構(gòu)C. Bohm & G. Jacopini, Flow Diagrams,

2、Turing Machines and Languages with Only Two Formation Rules, Communications of the ACM, vol9(5) May 1966, pp 366-371.分支語句#include using namespace std; int main()float weight = 0, height = 0, healthRate = 0;cin weightheight;healthRate = weight / (height*height);if (18 = healthRate)&(healthRate = 25)

3、cout 體重適中！ endl;else if (25 healthRate)&(healthRate = 30)cout 超重！注意控制！ endl; else if ( 30 healthRate)&(healthRate = 35)cout 肥胖！減肥吧！ endl;else if (35 healthRate)&(healthRate = 40)cout 重度肥胖！別吃了！ endl;elsecout 請(qǐng)直接撥打120！ endl;return 0;分支語句#include using namespace std; int main()int year = 0;cin year;if

4、(year % 4 = 0)if (year % 100 = 0)if (year % 400 = 0)cout Y;elsecout N;elsecout Y;elsecout N;return 0;if 語句使用須知在執(zhí)行 if 語句前先對(duì)表達(dá)式求解if ( )內(nèi)可以是任意的數(shù)值類型(包括整型、實(shí)型、字符型、指針型數(shù)據(jù))if (a)coutaendl；if (3)cout“OK”endl；若表達(dá)式的值為0，按“假”處理若表達(dá)式的值為 非0，按“真”處理多分支語句Switch語句的一般形式如下：switch(表達(dá)式)case常量表達(dá)式1:語句1; case常量表達(dá)式2:語句2;case常量表

5、達(dá)式n:語句n;default: 語句n1;當(dāng)表達(dá)式的值與某一個(gè)case后面的常量表達(dá)式的值相等時(shí)，就執(zhí)行此case后面的語句，若所有的case中的常量表達(dá)式的值都沒有與表達(dá)式的值匹配的，就執(zhí)行default后面的語句。#include using namespace std; int main()char grade = a; cingrade; switch (grade)case a: cout 85100 endl; case b: cout 7084 endl; case c: cout 6069 endl; case d: cout 60 endl; default: cout e

6、rror endl;return 0;#include using namespace std; int main()char grade = a; cin grade; switch (grade)case a: cout 85100 endl; break; case b: cout 7084 endl; break; case c: cout 6069 endl; break; case d: cout 60 endl; break; default: cout error endl;return 0;#include using namespace std; int main()cha

7、r grade = a; cin grade; switch (grade)case a: cout 85100 endl; case b: cout 7084 endl; case c:case d:case e:case f: cout 6069 endl; case g: cout 60 endl; default: cout error endl;return 0;#include using namespace std; int main()char grade = a; cin grade; switch (grade)case a: cout 85100 endl; case b

8、: cout 7084 endl; case c:case d:case e:case f: cout 6069 endl; case g: cout 60 endl; break;default: cout error endl;return 0;#include using namespace std; int main()char grade = a; cin grade; switch (grade)case a: cout 85100 endl; default: cout error endl; case b: cout 7084 endl; case c:case d:case

9、e:case f: cout 6069 endl; case g: cout 60 endl;return 0;#include using namespace std; int main()char grade = a; cin grade; switch (grade)case a: cout 85100 endl; default: cout error endl; case b: cout 7084 endl; case c:case d:case e:case f: cout 6069 endl; case g: cout 60 endl;return 0;思考與練習(xí)問題：學(xué)校要求實(shí)

10、行成績(jī)等級(jí)制度。現(xiàn)在已經(jīng)有同學(xué)們的百分制成績(jī),要求按照百分制成績(jī)輸出相應(yīng)的等級(jí)成績(jī). 90- 100為A, 8090分為B,7080分為C,6070分為D,60分以下為E。最直接的辦法：輸入成績(jī)；判定成績(jī)是否：90=成績(jī)=100判定成績(jī)是否：80=成績(jī)90如果用switch語句，如何解決？#include using namespace std; int main()int score, num;cout please give the score score; num = score / 10; switch (num)case 10: cout A endl; case 9: cout A

11、 endl; case 8: cout B endl; case 7: cout C endl; case 6: cout D endl; default: cout E endl;return 0;#include using namespace std; int main()int score, num;cout please give the score score; num = score / 10; switch (num)case 10: cout A endl; break; case 9: cout A endl; break; case 8: cout B endl; break; case 7: cout C endl; break; case 6: cout D endl; break; default: cout E endl;return 0;#include using namespace std; int main()int score, num;cout please give t