Linux C 程序 (ONE)

 1 vi first.c  //linux新建文件
 2 
 3 #include<stdio.h>
 4 
 5 int main() {
 6     printf("welcome to Linux ,this is the first C program!");    
 7     return 0;
 8 }
 9 
10 编译；gcc -o first first.c //linux编译文件
11 执行: ./first //linux执行文件

 1 vi second.c
 2 
 3 #include<stdio.h>
 4 int main() {
 5     int x , y , sum ;
 6     x = 100 ;
 7     y = 200 ; 
 8     sum = x + y ; 
 9     printf("sum is %d",sum);
10     return 0;
11 }
12 //编译执行命令与第一支C程序相同。

 1 #include<stdio.h>
 2 
 3 int main() {
 4     short int i;
 5     int j;
 6     long int k;
 7     int a,b,c;
 8     a = sizeof(i);
 9     b = sizeof(j);
10     c = sizeof(k);    
11     
12     printf("a is %d\n",a);
13     printf("b is %d\n",b);
14     printf("c is %d\n",c);
15     
16     //return 0; don‘t write return is OK?
17 }
18 output :
19 a is 2
20 b is 4
21 c is 4

 1 #include<stdio.h>
 2 
 3 int main(){
 4         float i ;
 5         double j;
 6         int a , b ;
 7         a = sizeof(i);
 8         b = sizeof(j);
 9         printf("a is %d \n b is %d \n",a , b);// bit number
10         
11         
12         float c = 88888.88888;
13         double d = 88888888888.88888888;
14         printf("c is %f \n d is %f \n",c,d);//%f小数最多输出六位
15         
16 }
17 
18 output:
19 a is 4
20 b is 8
21 c is 88888.890625 //i是单精度浮点数，有效位数为7，整数占据5位，小数占2位，第二位位四舍五入结果，后面均为无效数字
22 d is 88888888888.888885//j双精度，有效16位，整数占11位，小数占5位，后面为无效数。

 1 //C语言字符用‘‘单引号:eg : ‘A‘
 2 //转义字符：\n,换行，相当于enter
 3 //          \t,跳到下一个tab位置，相当于tab键
 4 //                    \b,退格，将当前位置移到前一列，相当于backspace
 5 //                    \\,反斜杠字符
 6 //                    \‘,单引号字符
 7 //                    \",双引号字符
 8 //                    \0,空字符，用在字符串中
 9 //                    \ddd,一到三位8进制代表的字符，如\101代表字符A
10 //                    \xhh,1到2位十六进制代表的字符，如\x41代表字符A
11 //字符变量定义：char c1 , c2 = ‘A‘; 占1字节,8bit,   ‘\n‘是一个转义字符
12 
13 #include<stdio.h>
14 
15 int main(){
16     int c1 ,c2 ; 
17     char c3;
18     printf("c3 is %d \n",sizeof(c3));
19     
20     c1 = ‘a‘ - ‘A‘;
21     c2 = ‘b‘ - ‘B‘;
22     c3 = ‘c‘ - 32;
23     
24     printf("c1 is %d and c2 is %d \n" , c1 ,c2);
25     printf("c3 is %d and %c \n",c3,c3);
26     return 0;
27 }
28 
29 
30 output:
31 c3 is 1
32 c1 is 32 and c2 is 32
33 c3 is 67 and C