problem with getchar() in C

Question

Well am learning C, and this is probably the stupidest question, but here it comes:

I'm using "getchar()" to stop the command windows so I can see the exercises am doing but it just don't work. heres a sample:

#include <stdio.h>

int main()
{
    int value;
    printf("1. option 1.\n2. option 2.\n3. option 3.\n4. Exit\n\nMake an option: ");
    scanf("%d", &value);
    switch (value)
    {
        case 1:
            printf("you selected the option 1.");
            break;
        case 2:
            printf("you selected the option 2.");
            break;
        case 3:
            printf("you selected the option 3.");
            break;
        case 4:
            printf("goodbye");
            break;
        default:
            printf("thats not an option");
            break;
    }
    getchar();
    return 0;
}

this is the output:

1. option 1.
2. option 2.
3. option 3.
4. Exit.

Make an option: 1

you selected the option 1.

Process returned 0 (0x0) execution time : 3.453 s

Press any key to continue.

it doesn't wait for the input of "getchar()".

I'm on XP using minGW with codeblocks..

Answer 1

Can getchar be getting your carriage return that you enter after the 1?

Answer 2

Your scanf only ate the number but not the trailing newline. Putting a newline or white space after the %d will then give you the opposite problem, reading too far.

This is why people don't like scanf.

I would suggest reading an actual line (use fgets(3)) and then using sscanf() to scan the string.

Answer 3

in order for your program to work, you should "flush" your input stream before calling getchar() with a call to fflush(stdin). What this does is, when you type in you keyboard a number and then the return key, the input buffer gets both characters, for example '1' and '\n', and your call to scanf gets only '1' so the '\n' remains in the input buffer. When you call getchar, you are "gettin" that remaining '\n'. Flushing the input discards all the buffer.

Answer 4

The getchar() is reading the \n from the keyboard in scanf - see here for more info

Answer 5

I think you input a enter after inputting "1". It will be accepted by the getchar().So you can solve the problem simply by add a additional getchar() after the original one(just before the "return 0;").

Answer 6

First of all, do not use fflush() to clear an input stream; the behavior is undefined:

7.19.5.2.2 If stream points to an output stream or an update stream in which the most recent operation was not input, the fflush function causes any unwritten data for that stream to be delivered to the host environment to be written to the file; otherwise, the behavior is undefined.

The problem is that the trailing newline is not being consumed by the "%d" conversion specifier, so it's being picked up immediately by the getchar(). There's no one best way to deal with this, but generally the approach is to read the whole line as text (using either fgets() or scanf() with a sized "%s" conversion specifier), which will consume the newline, then convert to the target data type using sscanf() or strtol() or strtod().

Answer 7

#include <stdio.h> 
#include<conio.h>
void main() 
{ 
    int value; 
    printf("1. option 1.\n2. option 2.\n3. option 3.\n4. Exit\n\nMake an option: "); 
    scanf("%d", &value); 
    switch (value) 
    { 
        case 1: 
            printf("you selected the option 1."); 
            break; 
        case 2: 
            printf("you selected the option 2."); 
            break; 
        case 3: 
            printf("you selected the option 3."); 
            break; 
        case 4: 
            printf("goodbye"); 
            break; 
        default: 
            printf("thats not an option"); 
            break; 
    } 
    getch(); 
}