Thread: why do I need 2 getchar()'s?

I'm a total n00b to programming in general, so forgive me if this is a bad question, but I've been searching all over the place and can't quite find an answer for my particular problem.

I want to develop good coding habits as I'm learning, so I'm concerned about this very small problem I've run into. I have a simple program that reads 2 numbers and prints them on the screen. I'm using the getchar() function to stop the output from closing, instead of the system(pause), which I understand is the right way. However, it seems that it doesn't work unless I put 2 getchar()'s at the end of the program, and I can't quite figure out why. Here's what I've got:

Code:

#include <stdio.h>

int main()
{
    int a, b;
    
    printf("Please enter a number: ");
    scanf("%d", &a);
    printf("\n\nPlease enter another number: ");
    scanf("%d", &b);
    printf("\n\nHello, World!  You entered %d and %d!", a, b);
    getchar();
    getchar();
    return 0;
}

If I only use 1 getchar() then the program closes after entering the numbers. What am I missing here?

Thanks!

After reading up on the scanf() function, I had considered that, but if that's the case, then I would have assumed that adding the 2nd number into the program would have then required 3 getchar()'s at the end, but that doesn't seem to be the case? How come the 2nd getchar() doesn't consume the 2nd newline, requiring me to have a 3rd one?

I know I could avoid these by running from the command line, but it's very convenient to run them from my compiler, and I also want to make sure that I fully understand exactly what's going on here.

Ah, I see, so scanf() is smart enough to tell between a \n and a number, and throws out what it finds while it's searching for valid data? That makes perfect sense, that little detail wasn't in the beginner's tutorial....I think I understand now.

Thanks to everyone who replied, I appreciate it

Originally Posted by parx86

Ah, I see, so scanf() is smart enough to tell between a \n and a number, and throws out what it finds while it's searching for valid data? That makes perfect sense, that little detail wasn't in the beginner's tutorial....I think I understand now.

Thanks to everyone who replied, I appreciate it

Sort of: it will ignore whitespace (spaces, tabs, newlines, etc.) at the beginning -- it won't throw away a 'q', it will just stop.

I see what you mean, I tried running the program again inserting random amounts of spaces in front of my entries, and it always trims it to just the numbers. However, if I put tabs and spaces AFTER the numbers, the getchar() function doesn't stop the program like before, because it's absorbing what came AFTER my input, correct?

OK, I think I have a good understanding of what's going on here, I'm sure I'll have another question very soon

Thanks everyone for your help!