第4章+程序流程设计PPT文档格式.ppt
《第4章+程序流程设计PPT文档格式.ppt》由会员分享,可在线阅读,更多相关《第4章+程序流程设计PPT文档格式.ppt(60页珍藏版)》请在冰豆网上搜索。
if(a=b&
x=y)printf(“a=b,x=y”);
if(3)printf(“OK”);
if(a)printf(“%d”,a);
l说明:
uif后面的表达式类型任意uif(x)if(x!
=0)if(!
x)if(x=0)u语句可以是复合语句例考虑下面程序的输出结果:
#includemain()intx,y;
scanf(“%d,%d”,&
x,&
y);
if(xy)x=y;
y=x;
elsex+;
y+;
printf(“%d,%dn”,x,y);
CompileError!
vif语句嵌套:
l一般形式:
if(expr1)if(expr2)statement1elsestatement2elseif(expr3)statement3elsestatement4内嵌if内嵌ifif(expr1)if(expr2)statement1elsestatement2内嵌ifif(expr1)if(expr2)statement1elsestatement3内嵌ifif(expr1)statement1elseif(expr3)statement3elsestatement4内嵌if例输入两数并判断其大小关系/*ch4_3.c*/#includemain()intx,y;
printf(Enterintegerx,y:
);
scanf(%d,%d,&
if(x!
=y)if(xy)printf(XYn);
elseprintf(XYn);
elseprintf(X=Yn);
运行:
Enterintegerx,y:
12,23XYEnterintegerx,y:
12,12X=Ylifelse配对原则:
缺省时,else总是和它上面离它最近的未配对的if配对if()if()if()else.else.else.例:
if(a=b)if(b=c)printf(“a=b=c”);
elseprintf(“a!
=b”);
修改:
实现ifelse正确配对方法:
加例考虑下面程序输出结果:
main()intx=100,a=10,b=20;
intv1=5,v2=0;
if(ab)if(b!
=15)if(!
v1)x=1;
elseif(v2)x=10;
elsex=-1;
printf(“%d”,x);
结果:
-1switch语句(开关分支语句)v一般形式:
switch(表达式)caseE1:
语句组1;
break;
caseE2:
语句组2;
.caseEn:
语句组n;
default:
语句组;
v执行过程:
switch表达式语句组1语句组2语句组n语句组.E1E2Endefaultcasev说明:
lE1,E2,En是常量表达式,且值必须互不相同l语句标号作用,必须用break跳出lcase后可包含多个可执行语句,且不必加lswitch可嵌套l多个case可共用一组执行语句例switch(score)case5:
printf(“Verygood!
”);
case4:
printf(“Good!
case3:
printf(“Pass!
case2:
printf(“Fail!
default:
printf(“dataerror!
运行结果:
score为5时,输出:
Verygood!
Good!
Pass!
Fail!
dataerror!
例voidmain()intx=1,y=0,a=0,b=0;
switch(x)case1:
switch(y)case0:
a+;
case1:
b+;
printf(“na=%d,b=%d”,a,b);
a=2,b=1如:
main()intscore,grade;
printf(“Inputascore(0100):
scanf(“%d”,&
score);
grade=score/10;
/*将成绩整除10,转化成switch语句中的case标号*/switch(grade)case10:
case9:
printf(“grade=An”);
case8:
printf(grade=Bn);
case7:
printf(grade=Cn);
case6:
printf(grade=Dn);
case5:
case0:
printf(“grade=En”);
printf(“Thescoreisoutofrange!
n”);
4.3循环型程序设计概述C语言可实现循环的语句:
l用goto和if构成循环lwhile语句ldowhile语句lfor语句goto标号;
.标号:
语句;
goto语句及用goto构成循环vgoto语句一般格式:
例用if和goto语句构成循环,求/*ch5_1.c*/#includemain()inti,sum=0;
i=1;
loop:
if(i=100)sum+=i;
i+;
gotoloop;
printf(%d,sum);
sum=0+1sum=1+2=3sum=3+3=6sum=6+4sum=4950+100=5050循环初值循环终值循环变量增值循环条件循环体v功能:
无条件转移语句v说明:
l不能用整数作标号l只能出现在goto所在函数内,且唯一l只能加在可执行语句前面l限制使用goto语句while语句v一般形式:
while(表达式)循环体语句;
v执行流程:
expr循环体假(0)真(非0)whilev特点:
先判断表达式,后执行循环体v说明:
l循环体有可能一次也不执行l循环体可为任意类型语句l下列情况,退出while循环u条件表达式不成立(为零)u循环体内遇break,return,gotol无限循环:
while
(1)循环体;
例用while循环求/*ch5_2.c*/#includemain()inti,sum=0;
while(i=100)sum=sum+i;
循环初值循环终值循环变量增值循环条件循环体dowhile语句v一般形式:
do循环体语句;
while(表达式);
do循环体expr假(0)真(非0)whilev特点:
先执行循环体,后判断表达式v说明:
l至少执行一次循环体ldowhile可转化成while结构expr循环体假(0)真(非0)循环体While循环例用dowhile循环求#includemain()inti,sum=0;
dosum+=i;
while(i=100);
例while和dowhile比较/*ch5_4.c*/#includemain()inti,sum=0;
scanf(%d,&
i);
while(i=10);
main()inti,sum=0;
while(i=10)sum+=i;
for语句v一般形式:
for(expr1;
expr2;
expr3)循环体语句;
expr2循环体假(0)真(非0)forexpr1expr3vfor语句一般应用形式:
for(循环变量赋初值;
循环条件;
循环变量增值)循环体语句;
v说明:
lfor语句中expr1,expr2,expr3类型任意,都可省略,但分号;
不可省l无限循环:
for(;
)lfor语句可以转换成while结构expr1;
while(expr2)循环体语句;
expr3;
例用for循环求#includemain()inti,sum=0;
for(i=1;
i=100;
i+)sum+=i;
#includemain()inti=0;
for(i=0;
i10;
i+)putchar(a+i);
abcdefghij例:
)putchar(a+(i+);
putchar(a+i),i+);
main()inti,j,k;
for(i=0,j=100;
i=j;
i+,j-)k=i+j;
printf(%d+%d=%dn,i,j,k);
#includemain()charc;
(c=getchar()!
=n;
)printf(%c,c);
#includemain()inti,c;
i+=3)printf(%c,i+c);
例(for)梯形法求数值积分0yxaa+ha+iha+(i+1)hbf(x)/面积赋初值*/#includemain()floata,b;
doubles,h;
doublef(doublex);
intn,i;
printf(Inputintegralareaa,b:
scanf(%f,%f,&
a,&
b);
printf(Inputn:
n);
h=(b-a)/n;
s=0.5*h*(f(a)+f(b);
i=n-1;
i+)s=s+h*f(a+i*h);
printf(nThevalueis:
%lf,s);
doublef(doublex)return(sqrt(4.0-x*x);
循环的嵌套v三种循环可互相嵌套,层数不限v嵌套循环的执行流程
(1)while()while().
(2)dodowhile();
.while();
(3)while()dowhile();
.(4)for(;
)dowhile();
while().内循环外循环内循环v嵌套循环的跳转禁止:
l从外层跳入内层l跳入同层的另一循环l向上跳转例循环嵌套,输出九九表12345678912345678924681