苏小红c语言电子教案第四章

《苏小红c语言电子教案第四章》由会员分享，可在线阅读，更多相关《苏小红c语言电子教案第四章（31页珍藏版）》请在装配图网上搜索。

1、Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,2024/9/22,31,/38,,,,第,4,章 键盘输入,,和屏幕输出,本章学习内容,,,字符常量与转义字符,,,字符输出函数,putchar,(),,,字符输入函数,getchar,(),,,,数据的格式化输出函数,printf,(),,,数据的格式化输入函数,scanf,(),,字符常量,字符常量是用单引号括起来的一个字符,,'a',是字符常量，而

2、,a,则是一个标识符,,'3',表示一个字符常量，而,3,则表示一个整数,,转义字符,（,Escape Character,）,,一些特殊字符（无法从键盘输入或者另有他用）用转义字符表示,,,,,,,,字符型变量的取值范围取决于计算机系统所使用的字符集,,ASCII,（美国标准信息交换码）字符集,,规定了每个字符所对应的编码,,一个字符以其对应的,ASCII,码的二进制形式存储在内存中,,一个字节，保存一个字符（英文字母、数字、符号）,,字符常数就是一个普通整数，也可参与各种数学运算,,每个字符具有一个,0~255,之间的数值，可从,ASCII,表查出,,注意：,'5',和整数,5,的区别,,

3、'5',的,ASCII,码值是,53,字符常量,4.1,单个字符的输入,/,输出,通过调用标准库函数来实现,,,#,include,<,stdio.h,>,,字符输出函数,,putchar(ch,),,输出,一个,字符,ch,ch,为字符变量名,,字符输入函数,,getchar,(),,无参数,,函数值为从输入设备接收的字符,【,例,4.1】,大小写英文字母转换,Press a key and then press Enter: B↙,,b,,ch,=,ch,+ ('a' – 'A');,,,,,What does,this statement,mean?,,,4.2,数据的格式化屏幕输出,格

4、式,,printf,(,格式控制字符串,,,输出项表列,);,,printf,(,",a=,%d,b=,%f,",,,a, b,);,,,,,,,可以输出若干,任意类型,的数据,,函数名,可选输,,出表列,普通字符,格式,,说明,%c character,以字符形式输出单个字符,,%s string,输出一个字符串,,%d decimal,以带符号十进制整数输出,,%f float,以小数形式输出浮点数（,6,位小数）,,%e exponent,以标准指数形式输出（,6,位小数）,,%g,选用,%f,，,%e,中输出宽度较小的一种格式,,%o octal,以八进制无符号整数输出（无前导,0,）

5、,,%x hex,以十六进制无符号整数输出（无前导,0x,）,,%u unsigned,以十进制无符号整数输出,printf(),格式字符,【,例,4.2】,大小写英文字母转换,Press a key and then press Enter: B↙,,b, 98,m,表示数据占用的最小宽度,,数据宽度大于,m,，按实际宽度输出,,数据宽度小于,m,时，补空格,,n,对实数表示输出,n,位小数,,对字符串表示最多输出的字符个数,,l,长整型整数,，加在,d,、,o,、,x,、,u,前,,L long double,型数，加在,f,、,e,、,g,前,,-,,改变输出内容的对齐方式,,默认为

6、右对齐,printf,(),的格式修饰符,printf,(),的格式修饰符,Format for float:,%f,,,General format:,,,%,[<,最小域宽,> . <,小数位数,>],f,Example:,printf("Value is:%10.4f", 32.6784728);,,,Value is: 32.6785,,,,,,,,,10 characters,4 digits,printf,(),的格式修饰符,Example:,printf("Value is:%10f", 32.6784728);,,Value is: 32.678473,,,,,,,,1

7、0 characters,6 digits (default),Example:,printf("Value is:%.3f", 32.6784728,);,,,Value is:32.678,,,3 digits,printf,(),的格式修饰符,,,,,,,,Input r: 5.3↙,,printf,WITHOUT width or precision specifications:,,circumference = 33.300854, area = 88.247263,,printf,WITH width and precision specifications:,,circumfe

8、rence = 33.30, area = 88.25,【,例,4.3】,计算圆的周长和面积,,4.3,数据的格式化键盘输入,格式,,scanf,(,格式控制字符串,,,地址表列,);,,,scanf,(,",%,d,%f,", ,,格式字符,,指定输入数据类型,,输入数据,,地址表列,,非格式字符,,输入数据以,,,分隔,,没有时可以,空格,、,,Tab,或,回车,分隔,c,以字符形式输入单个字符,,s,输入字符串,,,以非空字符开始,,,遇第一个,,空白字符结束,,d,以带符号十进制形式输入整型数据,,f,以小数形式输入浮点数,,e,以标准指数形式输入,,o,以八进制无符号形式输入

9、（无前导,0,）,,x,以十六进制无符号形式输入（无前导,0x,）,scanf(),的格式字符,m,表示数据占用的宽度,,l,加在,d,、,o,、,x,、,u,前：输入长整型,,加在,f,、,e,前：输入双精度型,,L,加在,f,、,e,前：输入,long double,型,scanf,(),的格式修饰符,#,include,,main(),{,,int,a, b;,,scanf("%d %d", ,printf("a = %d, b = %d\n", a, b);,},问题,1,：当要求程序输出结果为,,,a = 12, b = 34,,时，用户应该如何输入数据？,,12 34↙,输入数据的

10、格式控制,——,例,4.4,#,include,,main(),{,,int,a, b;,,scanf("%d %d", ,printf("a = %d, b = %d\n", a, b);,},问题,2,：当限定用户输入数据以逗号为分隔符，即输入数据格式为：,12,34↙,,时，应修改程序中的哪条语句？怎样修改？,,,,输入数据的格式控制,——,例,4.4,#,include,,main(),{,,int,a, b;,,scanf("%d %d", ,printf("a = %d, b = %d\n", a, b);,},问题,3,：语句,scanf("%d,%d", ,修改为,scanf(

11、",a,=,%d,,b =,%d", ,,时，用户应该如何输入数据？,a = 12, b = 34↙,输入数据的格式控制,——,例,4.4,#,include,,main(),{,,int,a, b;,,scanf("%d %d", ,printf("a = %d, b = %d\n", a, b);,},问题,10,：如果程序第,5,行语句修改为,...,，那么结果又会如何呢？,输入数据的格式控制,——,例,4.4,,,a, b,#,include,,main(),{,,int,data1, data2, sum;,,char,op;,,printf("Please enter the

12、expression,data1 + data2\n");,scanf("%d%c%d",,printf("%d%c%d = %d\n",,data1, op, data2, data1+data2);,},Please enter the expression data1 + data2,,第,1,次测试,12 + 3↙,12 4199288 = 4199300,C,格式符的问题及解决,—,例,4.5,,,,,,,,,,#,include,,main(),{,,int,data1, data2, sum;,,char,op;,,printf("Please enter the express

13、ion,data1 + data2\n");,scanf("%d%c%d",,printf("%d%c%d = %d\n",,data1, op, data2, data1+data2);,},Please enter the expression data1 + data2,,第,2,次测试,12 3↙,12 3 = 15,,,,,,,,,,C,格式符的问题及解决,—,例,4.5,#,include,,main(),{,,int,data1, data2, sum;,,char,op;,,printf("Please enter the expression,data1 + data2\n"

14、);,scanf("%d%c%d",,printf("%d%c%d = %d\n",,data1, op, data2, data1+data2);,},Please enter the expression data1 + data2,,第,3,次测试,12+3↙,12+3 = 15,,,,,,,,,,C,格式符的问题及解决,—,例,4.5,#,include,,main(),{,,int,a;,,char,b;,,float,c;,printf("Please input an integer:");,scanf("%d", ,printf("integer: %d\n", a);,pri

15、ntf("Please input a character:");,scanf("%c", ,printf("character: %c\n", b);,printf("Please input a float number:");,scanf("%f", ,printf("float: %f\n", c);,},Please input an integer:,希望得到的运行结果,12↙,Please input an character,,:,a↙,Please input a float number:,3.5↙,integer:12,character,,:a,float number

16、:3.500000,C,格式符的问题及解决,—,例,4.6,#,include,,main(),{,,int,a;,,char,b;,,float,c;,printf("Please input an integer:");,scanf("%d", ,printf("integer: %d\n", a);,printf("Please input a character:");,scanf("%c", ,printf("character: %c\n", b);,printf("Please input a float number:");,scanf("%f", ,printf("float

17、: %f\n", c);,},Please input an integer:,结果好像很奇怪呀！,12↙,Please input an character,,:,a↙,Please input a float number:,3.5↙,integer:12,,float number:3.500000,C,格式符的问题及解决,—,例,4.6,,,,,,,#,include,,,main(),,{,,,int,a;,,,char,b;,,,float,c;,,printf("Please input an integer:");,,scanf("%d", ,,printf("integer:

18、 %d\n", a);,,printf("Please input a character:");,,,getchar();,/*,将存于缓冲区中的回车字符读入，避免被后面的变量作为有效字符读入*,/,,scanf("%,c,", ,,printf("character: %c\n", b);,,printf("Please input a float number:");,,scanf("%f", ,,printf("float: %f\n", c);,,},Please input an integer:,程序修改后得到的运行结果,12↙,Please input an character

19、,,:,a↙,Please input a float number:,3.5↙,integer:12,character,,:a,float number:3.500000,C,格式符的问题及解决,—,例,4.6,,,,,,,,,,,,#,include,,,main(),,{,,,int,a;,,,char,b;,,,float,c;,,printf("Please input an integer:");,,scanf("%d", ,,printf("integer: %d\n", a);,,printf("Please input a character:");,,scanf,(,“,

20、%c,”,,,,/*,第,2,种解决方案,:,在,%c,前加一个空格,*/,,printf("character: %c\n", b);,,printf("Please input a float number:");,,scanf("%f", ,,printf("float: %f\n", c);,,},C,格式符的问题及解决,—,例,4.6,,#,include,,main(),{,,int,data1, data2, sum;,,char,op;,,printf("Please enter the expression,data1 + data2\n");,scanf("%d,%c,%d",,printf("%d%c%d = %d\n",,data1, op, data2, data1+data2);,},12+3↙,12 + 3↙,12,↙,+,↙,3↙,再回头来看例,4.5,,,如何以任意分隔符输入加法算式？,格式输入函数常见错误,scanf,(,",%,d,%f,\n,",&a,&b,);,,scanf,(,",%,d,%f",,a,b,);,,scanf,(,",%7,.2f,",,,,,几点忠告,,不要拘泥于细节,,不要死记硬背,,在使用中慢慢掌握,注意！,本章节作业,P59 4.1 4.2 4.3,