C语言学习笔记[第9天]

四、字符串和格式化输入/输出

4. print()和scanf()

​ ■输入和输出函数，I/O函数

​ ■两函数都使用格式字符串和参数列表

4.1 print()函数

​ ■转换说明

​ 转换说明及其打印的输出结果

转换说明	输出
%a	浮点数、十六进制数和p计数法(C99/C11)
%A	浮点数、十六进制数和p计数法(C99/C11)
%c	单个字符
%d	有符号十进制整数
%e	浮点数，e记数法
%E	浮点数，e记数法
%f	浮点数，十进制计数法
%g	根据值的不同，自动选择%f或%e。%e格式用于指数小于-4或者大于或等于精度时
%G	根据值的不同，自动选择%f或%E。%E格式用于指数小于-4或者大于或等于精度时
%i	有符号十进制整数（与%d相同）
%o	无符号八进制整数
%p	指针
%s	字符串
%u	无符号十进制整整
%x	无符号十六进制整数，使用十六进制数0f
%X	无符号十六进制整数，使用十六进制数0F
%%	打印一个百分号

4.2 使用printf()

/* printout.c -- 使用转换说明 */
#include <stdio.h>
#define PI 3.141593
int main(void)
{
    int number = 7;
    float pies = 12.75;
    int cost = 7800;
    
    
    printf("The %d contestants ate %f berry pies.\n", number, pies);
    printf("The value of pi is %f.\n", PI);
    printf("Farewell! thou art too dear for my possessing,\n");
    printf("%c%d\n", '$', 2 * cost);
    
    return 0;
}
//The 7 contestants ate 12.750000 berry pies.
//The value of pi is 3.141593.
//Farewell! thou art too dear for my possessing,
//$15600

4.3 printf()的转换说明修饰符

/* width.c -- 字段宽度 */
#include <stdio.h>
#define PAGES 959
int main(void)
{
    printf("*%d*\n", PAGES);
    printf("*%2d*\n", PAGES);
    printf("*%10d*\n", PAGES);
    printf("*%-10d*\n", PAGES);
    
    return 0;
}
//*959*
//*959*
//*		959*
//*959	   *

// float.c -- 一些浮点型修饰符的组合
#include <stdio.h>

int main(void)
{
    const double RENT =3852.99;		//	const 变量
    
    printf("*%f*\n", RENT);
    printf("*%e*\n", RENT);
    printf("*%4.2f\n*", RENT);
    printf("*%3.1f*\n", RENT);
    
    printf("*%10.3f*\n", RENT);
    printf("*%10.3E*\n", RENT);
    printf("*%+4.2f*\n", RENT);
    printf("*%010.2f*\n", RENT);
	
    return 0;
}
//*3852.990000*
//*3852.990e+03*
//*3852.99*
//*3853.0*
//*  3852.990*
//* 3853E+03*
//*+3852.99*
//*0003852.99*

/* flags.c -- 演示一些格式标记 */
#include <stdio.h>
int main (void)
{
    printf("%x %X %#x\n", 31, 31, 31);
    printf("**%d**% d**% d**\n", 42, 42, -42);
    printf("**%5d**%5.3d**%05d**%05.3d**\n", 6, 6, 6, 6);
    
    return 0;
}
//1f 1F 0x1f
//**42** 42**-42**
//**    6**  006**00006** 006**

/* stringf.c -- 字符串格式 */
#include <stdio.h>
#define BLURB "Authentic imitation!"
int main(void)
{
    printf("[%2s]\n",BLURB);
    printf("[%24s]\n", BLURB);
    printf("[%24.5s]\n", BLURB);
    printf("[%-24.5s]\n", BLURB);
    
    return 0;
}
//[Authentic imitation!]
//[    Authentic imitation!]
//[                   Authe]
//[Authe                   ]

4.4转换说明的意义

​ 转换说明是翻译说明

​ ■转换不匹配

/* intconv.c -- 一些不匹配的整型转换 */
#include <stdio.h>
#define PAGES 336
#define WORDS 65618
int main(void)
{
    short num = PAGES;
    short mnum = -PAGES;
    
    printf("num as short and unsigned short: %hd %hu\n", num,num);
    printf("-num as short and unsigned short %hd %hu \n", mnum,mnum);
    printf("num as int and char:%d %c\n", num, num);
    printf("WORDS as int, short , and char: %d %hd %c\n",WORDS,WORDS, WORDS);
    
    return 0;
}
//num as short and unsigned short: 336 336
//-num as short and unsigned short -336 65200 
//num as int and char: 336 P
//WORDS as int, short , and char: 65618 82 R

​ ■混淆整型和浮点型

/* floatcnv.c -- 不匹配的浮点型转换 */
#include <stdio.h>
int main(void)
{
    float n1 = 3.0;
    double n2 = 3.0;
    long n3 = 2000000000;
    long n4 = 1234567890;
    
    printf("%.1e %.1e %.1e %.1e\n", n1, n2, n3, n4);
    printf("%1d %1d\n", n3, n4);
    printf("%1d %1d %1d %1d\n", n1, n2, n3, n4);
    
    return 0;
}
//3.0e+00 3.0e+00 3.1e+46 1.7e+266
//2000000000 1234567890
//0 1074266112 0 1074266112

​ ■printf()的返回值

/* prntval.c -- printf()的返回值 */
#include <stdio.h>
int main(void)
{
    int bph2o = 212;
    int rv;
    rv = printf("%d F is water's boiling point.\n", bph2o);
    printf("The printf() function printed %d characters.\n", rv);
    
    return 0;
}
//212 F is water's boiling point.
//The printf() function printed 32 characters.

​ ■打印较长的字符串

/* longstrg.c -- 打印较长的字符串 */
//方法一：多个printf()语句
//方法二: 用反斜杠(\)和Enter(或Return)键组合来断行
//方法三： ANSIC引入的字符串连接
#include <stdio.h>
int main(void)
{
    printf("Here's one way to print a");
    printf("long string.\n");
    printf("Here's anther way to print a\
		long string.\n");
    printf("Here's the newest way to print a"
          		"long string.\n");		/* ANSI  C	*/
    
    return 0;
}
//Here's one way to print a long string.
//Here's anther way to print a long string.
//Here's the newest way to print a long string.