Understanding of C language EOF

understand

EOF Is the end of the file , Is a macro definition （C All input and output operations in the language are designed according to the idea of reading files ）

utilize getchar And putchar Function can detect the input characters , If it is not the end of document indicator （ When reading files , When encountering the end position of the file or error in reading data, it will return EOF） Then copy the character to the output .

#include<stdio.h>
#include<stdlib.h>

int
main()
{
    int ch;
    int line;
    int at_begining;

    line =0;
    at_begining=1;

             /*
              * Read characters and process them one by one ;
              */
while( (ch = getchar()) != EOF ){
            /*
             * If we are at the beginning of a line , Print line number ;
             */
             if (at_begining==1){
                     at_begining = 0;
                     line += 1;
                     printf("%d",line);
            }

             /*
              * Print character , And detect the end of the line ;
              */  
              putchar( ch );
              if( ch == '\n')
                    at_begining = 1;
        }

        return EXIT_SUCCESS;
}

The source code of this case realizes ： Read a few lines of input from standard input . Each line of input should be printed on the output , The line number should be added to the front . When writing a program, try to make the input lines processed by the program unlimited .