嵌套循环渐近分析(Nested Loops Asymptotic analysis)

 我为此推荐GNU readline库 。 它负责获取输入行的繁琐工作，并允许用户使用退格键，左右箭头等编辑他的行，并使用向上箭头调用较旧的命令，甚至使用^ R搜索较旧的命令，等等。Readline安装了典型的类似linux的unix发行版，但如果你没有它，你可以在这里找到它 
 
 编辑：这是一个最小的readline示例： 
 
#include <stdio.h>
#include <readline/readline.h>
#include <readline/history.h>

int main(int argc, char ** argv)
{
    while(1)
    {
        char * line = readline("> ");
        if(!line) break;
        if(*line) add_history(line);
        /* Do something with the line here */
    }
}
 
 用gcc -o test编译test.c -lreadline -lncurses。 
 
 如果你不能使用readline，getline是另一种选择： 
 
#include <stdio.h>
int main()
{
    char * line = NULL;
    size_t len;
    while(getline(&line, &len, stdin) >= 0)
       printf("I got: %s", line);
}
 
 如果即使getline是不可接受的，你可以使用fgets。 它不会动态分配合适大小的缓冲区，所以太长的行会被截断。 但至少它是标准的C： 
 
#include <stdio.h>
int main()
{
    char buf[1000];
    while(fgets(buf, sizeof(buf), stdin)
        printf("I got: %s, line);      
}

I recommend the GNU readline library for this. It takes care of the tedious work of getting lines of input, and allows the user to edit his line with backspace, left and right arrows, etc, and to recall older command using the up arrow and even search for older command using ^R, etc. Readline comes installed with typical unix-like distributions like linux, but if you don't have it, you can find it here
 
Edit: Here is a minimal readline example:
 
#include <stdio.h>
#include <readline/readline.h>
#include <readline/history.h>

int main(int argc, char ** argv)
{
    while(1)
    {
        char * line = readline("> ");
        if(!line) break;
        if(*line) add_history(line);
        /* Do something with the line here */
    }
}
 
Compile with gcc -o test test.c -lreadline -lncurses.
 
If you can't use readline, getline is an alternative:
 
#include <stdio.h>
int main()
{
    char * line = NULL;
    size_t len;
    while(getline(&line, &len, stdin) >= 0)
       printf("I got: %s", line);
}
 
If even getline is unacceptable, you can use fgets. It will not dynamically allocate a buffer of suitable size, so too long lines will be truncated. But at least it is standard C:
 
#include <stdio.h>
int main()
{
    char buf[1000];
    while(fgets(buf, sizeof(buf), stdin)
        printf("I got: %s, line);      
}