Put char into array by using pointer in c

Question

I have a problem, they gave me a task. They told us that we must use a pointer to put the value from the keyboard to array and then print that array.

I try to create that, but I don't know why this is wrong. I define my array then I get value and put that value into an array.

#include <stdio.h>
#include <stdlib.h>
#define N 10000 // Maximum array size


int main ()
{
    char keyboardArray[N];    
    char *r;            
    r = keyboardArray;
    while( (*r++ = getchar()) != EOF );
    printf("You write %s", r);

    return 0;
}

Barmar · Accepted Answer · 2020-04-14 19:47:15Z

2

You have several problems:

At the end of the loop, r points to the end of the string, not the beginning. So printing r won't print the string that was entered. You should print the keyboardArray rather than r.
You're never adding a null terminator to the string, so you can't use the %s format operator.
getchar() returns int, not char -- this is needed to be able to distinguish EOF from ordinary characters. So you need to read into a different variable before storing into the array.

int main ()
{
    char keyboardArray[N];    
    char *r;    
    int c;        
    r = keyboardArray;
    while( (c = getchar()) != EOF ) {
        *r++ = c;
    }
    *r = '\0'; // Add null terminator
    printf("You write %s\n", keyboardArray);
}

Note that this will read until EOF, so the user will have to type a special character like Control-d (on Unix) or Control-z (on Windows) to end the input. You might want to check for newline as well, so they can enter a single line:

while ((c = getchar()) != EOF && c != '\n') {

edited Apr 14, 2020 at 19:47

answered Apr 14, 2020 at 19:42

Barmar

789k57 gold badges554 silver badges669 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Davislor Over a year ago

Make that while (r < keyboardArray + N - 1 && (c = getchar()) != EOF && c != '\n'). Always, always, always check for buffer overflow in C!

Davislor Over a year ago

I know this is a beginner question, but it is a good habit to get into.

Vlad from Moscow · Accepted Answer · 2020-04-14 19:51:26Z

1

I think that in any case you need an intermediate variable that will accept a read character.

Also you need to append the entered sequence of characters with the terminating zero.

For example

#include <stdio.h>

#define N 10000 // Maximum array size

int main( void )
{
    char keyboardArray[N];    
    char *r = keyboardArray;

    for ( int c; 
          r + 1 < keyboardArray + N && ( c = getchar() ) != EOF && c != '\n';
          ++r )
    {
        *r = c;
    }

    *r = '\0';

    printf( "You write %s\n", keyboardArray );
}

edited Apr 14, 2020 at 19:51

answered Apr 14, 2020 at 19:45

Vlad from Moscow

313k27 gold badges204 silver badges358 bronze badges

Collectives™ on Stack Overflow

Put char into array by using pointer in c

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related