A data type
Second, input and output statements
Example:
scanf("%d",&a);
printf("%d",a);
Different types of data have their corresponding format type:
. 1, int % D takes an integer value and it is represented as a signed decimal integer
long% ld is a long integer
2 , % O unsigned octal integer (no output prefix 0)
3,% u unsigned decimal integer
4,% x / X unsigned hexadecimal integer Example:
printf("%x\n", i); printf("%X\n", i); printf("%#x\n", i); printf("%#X\n", i);
Respectively output 2f 2F 0x2f 0X2F
. 5, a float , and double single-precision floating-point ( % F ) and double precision floating point ( % LF)
. 6 , % .mf output real decimal places of m bits, m has a front attention points.
. 7 , % E / E number, represented here scientific notation "e" is represented by a case when the output "e" capitalization
8,% c character. Can according to the digital input ASCII code into corresponding respective character
Example:
#include <stdio.h> int main() { char i='A'; printf("%c",i); return 0; }
A character output
If the output is a control character '% d', the output value of the ASCII code corresponding to 'A'
9,% s string. Output string of characters until a null character string (string '\ 0' ends, this '\ 0' i.e. null character)
Example:
#include <stdio.h> int main() { char i[]="ABC"; printf("%s",i); return 0; }
Output string of ABC
10,% p to the output pointer, output variable address in hexadecimal notation
Example:
#include <stdio.h> int main () { int I = . 5 ; the printf ( " % D \ n- " , I); // output decimal integer the printf ( " % P " , I); // hexadecimal output pointer form the printf ( " % P " , & I); // output variable memory address return 0 ; }
11,% n number of characters before this character until the total output, no output text
12 %% without conversion, outputting the character '%' (percent) itself
13,% m print error errno value corresponding to the content, (Example: printf ( "% m \ n ");
Third, the escape character
|
Escape character
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significance
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ASCII value (decimal)
|
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\a
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Bell (BEL)
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007
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\b
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Backspace (BS), the current position to the previous column
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008
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\f
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Feed (FF), the current position to the beginning of the page
|
012
|
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\n
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Line feed (LF), the current position to the beginning of the next line
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010
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\r
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A carriage return (CR), the current position to the beginning of the line
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013
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\t
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Horizontal tab (the HT) (TAB jumps to the next position)
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009
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\ v
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Vertical tabulation (VT)
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011
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\\
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Represent a backslash character '\'
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092
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\'
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On behalf of a single quote (apostrophe) character
|
039
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\"
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It represents a double quote character
|
034
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| \? | On behalf of a question mark | 063 |
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\0
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Null character (NUL)
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000
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\ooo
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Any character 1-3 octal number represented
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Three octal
|
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\ socialization
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Hexadecimal character represents any
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Hex
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String needs to be used to represent \\ \ first \ represents the escape, the second \ character represents the
Example:
#include <stdio.h> main() { printf("hello world"); printf("\n"); printf("hello world"); printf("\a"); //响铃 printf("\b"); //退格 printf("\n"); printf("\f"); //翻页 printf("\n"); printf("hello world"); printf("\r"); //回车 printf("\t"); //水平制表,跳到下一个TAB位置 printf("hello world"); system("\"C:\\Program Files\\Tencent\\QQ\\Bin\\QQScLauncher.exe\""); // ‘\\’和‘"""’表示不出来用\来转义 getchar(); //等待响应 return 0; }
四、常量与变量
1、变量的命名规则
• 标识符：
程序中用于标识常量、变量、函数的字符序列组成
变量使用之前一定要初始化，如果变量不初始化，就会默认读取垃圾数据， 有些垃圾数据
会导致程序崩溃。所以，变量使用之前，必须初始化。
2、定义常量
• 定义常量PI的两种方式：
#define PI 3.14159; const float PI=3.14159; //const定义的常量不能修改，是只读数据
例：
#include <stdio.h> int main() { #define NAME "朱健康" const int AGE=22; printf("我的名字: %s",NAME); printf("\n"); printf("我的年龄：%d",AGE); return 0; }
#include <stdio.h> //自由落体运动 g=9.8 //输入时间，输出自由落体运动的距离 int main() { #define g 9.8 float t,s; printf("自由落体时间：\n"); scanf("%f",&t); s=1/2.0*g*t*t; printf("自由落体的距离: %f",s); return 0; }
五、进制的计算
1、二进制、八进制转换
• 例 (1101001)2=(001,101,001)2=(151)8
• 例 (246)8=(010,100,110)2=(10100110)2
2、十进制、二进制转换
- 0.625 * 2 = 1.25 取整1
- 0.25 * 2 = 0.5 取整0
- 0.5 * 2 = 1 取整1
3、位、字节、字
六、整型常量
• 十进制整数：
• 八进制整数：
• 十六进制整数：
• 长整型常量：
七、整型变量
八、浮点型常量
• 十进制小数形式：
• 指数形式：
• 实型常量的类型细分：
九、浮点型变量
#include <stdio.h> #include <math.h> //给出三角形的三边长，求三角形面积。 int main() { double a,b,c; double p,s; scanf("%lf %lf %lf",&a,&b,&c); //double的格式化类型为%lf if(a+b>c && a+c>b && b+c>a) { p=(a+b+c)/2.0; s=sqrt(p*(p-a)*(p-b)*(p-c)); printf("a=%lf\tb=%lf\tc=%lf\n",a,b,c); printf("三角形面积：%f",s); } else { printf("三边不能构成三角形"); } return 0; }