Why is getchar() reading '\n' after a printf statement?

Question

I'm prompting the user to enter the length of an array, initializing a char[] array with this input, and then prompting the user to type a message to enter into the char[] array.

I'm reading the first character of the user's message with getchar().

However, getchar() is reading the new-line escape '\n' before it is reading any user input. It seems to be getting '\n' from the previous printf statement that prompts the user...

Here is the relevant code:

#include <stdio.h>

int main(void) {

    int len = 0,
        originalLen = 0;

    printf("\n\nWhat is the length of the array? ");
    scanf("%d", &originalLen);
    char str[originalLen]; // intitializing the array

    printf("Enter a message to enter into the array: ");
    char target = getchar();
    str[len] = target;

    // why is getchar() reading '\n'?
    if (target == '\n') {
        printf("\n...what happened?\n");
    }
    return 0;
} // end of main

Some programmer dude · Accepted Answer · 2013-02-08 03:31:08Z

4

It's because the previous scanf does not read the newline after the number.

This can be solved two ways:

Use e.g. getchar to read it
Add a space after the scanf format (e.g. scanf("%d ", ...))

answered Feb 8, 2013 at 3:31

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

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

2 Comments

Ian Campbell Over a year ago

Thanks @Joachim, so it seems that you have to use the extra space hack for scanf... is there a better alternative, or is this professionally accepted?

Some programmer dude Over a year ago

@IanCampbell I wouldn't call it a "hack", it simply tells scanf to read (and discard) whitespace. As for "professionally accepted", I've used it myself a lot and seen it in a lot of other code as well, so it's not uncommon.

Simon Broadhead · Accepted Answer · 2013-02-08 03:33:48Z

3

You can use getchar in a loop to flush out stdin before reading the next character.

while((target = getchar()) != '\n' && target != EOF)

answered Feb 8, 2013 at 3:33

Simon Broadhead

3,48323 silver badges19 bronze badges

Comments

Alok Save · Accepted Answer · 2013-02-08 03:32:05Z

2

When you enter the number and hit the ENTER key, a number and a character are placed in the input buffer, they are namely:

The entered number and
The newline character(\n).

The number gets consumed by the scanf but the newline remains in the input buffer, which is read by getchar().

You need to consume the \n before calling getchar() by using:

scanf("%d ", &originalLen);
         ^^^

This tells scanf to read the number and an additional character, which is \n.

answered Feb 8, 2013 at 3:32

Alok Save

208k56 gold badges449 silver badges540 bronze badges

4 Comments

Ian Campbell Over a year ago

Ah thanks @Alok, that makes sense -- it's hitting the ENTER key that adds the '\n' character. Is scanf frowned upon for this reason?

Alok Save Over a year ago

@IanCampbell: Yes, for this and many more. such as: type safety, input validation and so on . It should be avoided while reading characters and strings but it is okay to use it for simple numeric inputs.

Ian Campbell Over a year ago

Thanks @Alok, interesting... so what's a better alternative to scanf for characters and Strings?

Alok Save Over a year ago

@IanCampbell: fgets always!

Collectives™ on Stack Overflow

Why is getchar() reading '\n' after a printf statement?

3 Answers 3

2 Comments

Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related