print multiple lines by getchar and putchar

Question

Im a beginner learning The C Programming language and using Microsoft visual C++ to write and test code.

Below program in C from text(section 1.5.1) copy its input to its output through putchar() and getchar():

#include <stdio.h>
int main(void)
{   int c;
    while ((c = getchar()) != EOF)
         putchar(c);
    return 0;}

The program print characters entered by keyboard every time pressing ENTER.As a result,I can only enter one line before printing. I can't find a way to enter multi-line text by keyboard before printing.

Is there any way and how to let this program input and output multi-line text from keyboard?

Sorry if this is a basic and ignorant question.

Appreciate your attention and thanks in advance.

use fgets to read in a line of input, then concatenate the input lines using strcat. — suspectus, Jul 18 '13 at 08:03
On windows you can enter new-line character by pressing alt+10. — , Jul 18 '13 at 08:15

Nobilis · Accepted Answer · 2013-07-18T08:24:42.050

Some clever use of pointer arithmetic to do what you want:

#include <stdio.h>  /* this is for printf and fgets */
#include <string.h> /* this is for strcpy and strlen */
#define SIZE 255 /* using something like SIZE is nicer than just magic numbers */

int main()
{
    char input_buffer[SIZE];        /* this will take user input */
    char output_buffer[SIZE * 4];   /* as we will be storing multiple lines let's make this big enough */

    int offset = 0; /* we will be storing the input at different offsets in the output buffer */

    /* NULL is for error checking, if user enters only a new line, input is terminated */
    while(fgets(input_buffer, SIZE, stdin) != NULL && input_buffer[0] != '\n') 
    {
        strcpy(output_buffer + offset, input_buffer); /* copy input at offset into output */
        offset += strlen(input_buffer);               /* advance the offset by the length of the string */
    }

    printf("%s", output_buffer); /* print our input */

    return 0;
}

And this is how I use it:

$ ./a.out 
adas
asdasdsa
adsa

adas
asdasdsa
adsa

Everything is parroted back :)

I've used fgets, strcpy and strlen. Do look those up as they are very useful functions (and fgets is the recommended way to take user input).

Did you run the program in Linux?Seems that I should use Linux instead of windows for programming. — user2593692, Jul 19 '13 at 00:16
Yes, that was run under Linux, but I see no reason why you couldn't run this under Windows. I've not used any special headers or custom OS behaviour :) But otherwise I recommend using Linux for C programming as its most popular compiler GCC supports the C99 standard. VC++ only implements C90 and there no plans to support any newer C standards. And this is a personal opinion of course but your assumption is correct in that Linux makes it easier to do programming, not just for C. — Nobilis, Jul 19 '13 at 01:01

score 0 · Answer 2 · answered Jul 18 '13 at 08:10

Here as soon as you type '+' and press enter all the data you entered till then is printed. You can increase the size of array more then 100

#include <stdio.h>
    int main(void)
    {   int c='\0';
         char ch[100];
         int i=0;
        while (c != EOF){
          c = getchar();
          ch[i]=c;
      i++;

            if(c=='+'){

            for(int j=0;j<i;j++){
                printf("%c",ch[j]);
            }
        }
    }
        return 0;


    }

You can put a condition on '+' char or whatever character you would like to represent print action so that this character is not stored in the array ( I have not put any such condition on '+' right now)

score 0 · Answer 3 · answered Jul 18 '13 at 08:28

Use setbuffer() to make stdout fully buffered (up to the size of the buffer).

#include <stdio.h>
#define BUFSIZE 8192
#define LINES 3
char buf[BUFSIZE];
int main(void)
{   int c;
    int lines = 0;
    setbuffer(stdout, buf, sizeof(buf));
    while ((c = getchar()) != EOF) {
         lines += (c == '\n');
         putchar(c);
         if (lines == LINES) {
              fflush(stdout);
              lines = 0;
         }}
    return 0;}

score -1 · Answer 4 · answered Jul 18 '13 at 08:17

Could you use the GetKeyState function to check if the SHIFT key is held down as you press enter? That was you could enter multiple lines by using SHIFT/ENTER and send the whole thing using the plain ENTER key. Something like:

#include <stdio.h>
int main(void)
{    int c;
     while (true){
         c = getChar();
         if (c == EOF && GetKeyState(VK_LSHIFT) {
              putchar("\n");
              continue;
         else if(c == EOF) break;
         else {
              putchar(c);
     }
 }

print multiple lines by getchar and putchar

4 Answers4

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