Thread: print specified line twice from stdin

First you will need to modify your program so that it stores the line being read (at least when you are on line number 4). Once you have the stored line, you can print it using printf, puts or some other "print string" function.

--
Mats

Originally Posted by nonshatter

Hi, I'm a complete C newbie, so i'm sorry if this sucks!

Basically, I have a paragraph of text which is being streamed through stdin. All I need the program to do is print the forth line twice using a variable '4p'.

I have a VERY simple line counter program below... How can it be modified to achieve the requirement?

Code:

#include < stdio.h>

void main()
{
	int c, nl = 0;
	
	while ( (c = getchar()) != EOF )
	{
	
	if (c == '\n') nl++;
	}
	
	printf("number of lines = %d\n",nl);
	  
}

A point in the right direction would be most helpful. Thanks

main returns int so void main is non-standard, it should be int main(void).

Code:

#include <stdio.h>

#define LINENUMBER  4   /* which line need to print */
#define COUNT       1   /* increase counter for line */
#define NOCOUNT     0   /* pause counter for line */

/* read a standard input, prints 4th line
   and number of all lines */
main()
{
    int c, nl = 0, state = COUNT;
    
    while ((c = getchar()) != EOF) {
        if (state == COUNT) {
            state = NOCOUNT;
            nl++;
        }    
        if (c == '\n')
            state = COUNT;
        if (nl == LINENUMBER)
            putchar(c);    
    }
    printf("number of lines = %d\n",nl);
    return 0;
}

1. Don't give out solutions to homework problems - it helps no one.
2. Your code don't even solve the problem of printing the line twice.
3. Is it not a bit of a Rube Goldberg solution?

--
Mats

4. and read the FAQ Cprogramming.com FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[])

Originally Posted by c.user

int main(int argc, char *argv[]); is not need for С89 and some compilers don't know a С99 standard, but all know C89

So? It is not like compiling with respect to C89 would cause a compiler to choke when main is explicitly declared to have a return type of int.

Originally Posted by c.user

I write in C, if compiler compiles my C like C++ it is its problem

This has nothing to do with C++. Even when you do not compile as C99, consider the motivation: explicitly declaring the return type as int improves readability and helps in maintenance by making it more obvious that the intention is to declare the function as returning an int, and thus rules out the possibility that the omission is due to carelessness rather than reliance on default int.

Originally Posted by c.user

in gcc i have no warnings, because it is know that there was C89 many years ago

Increase your warning level to -Wall (without -std=c99 of course, since that would separately activate the warning).

Originally Posted by c.user

If I write to C99 or C++ sometime, I use int main(int argc, char *argv[]) because they need it by their standards, but if I write in C89 its standard better

Just to check: are you aware that these two programs are valid in C89? (In fact, these correspond the closest to the actual text of section 2.1.2.2 of the 1989/1990 version of the C Standard.)

Code:

int main(void)
{
    return 0;
}

Code:

int main(int argc, char *argv[])
{
    return 0;
}

It seems to me that what you are saying is that C89 forbids functions from being declared with int return type stated explicitly, but of course that would be rubbish.

Originally Posted by c.user

(I use int i; for (i = 0 ... not for(int i = 0 ... because I need C89 and I don't use // only /* */ because I don't want mix standards)

I think you are confused: there is no "mixing of standards" here. The use of an explicit int return type is something permitted by C89 as well. The mixing of declarations and other code and the use of // style comments are indeed features not present in C90 but present in C99 (and C++), but those are different issues altogether. I would also recommend against their use if there is a need to support compilers that only compile with respect to C89.