Thread: The scanf function

First of all, I'm new to C (having a course about embedded systems at a university in Denmark).

I've a program which converts a BMP picture to grayscale and uses filters to create edge detection and some other fun stuff.

I need to create something as simple as a menu like:

Press an integer to pick a menupoint:
1) Load image
2) Modify image
3) Save image

When I use the following code I get a problem with the scanf. It pops up before anything else in my code, meaning when I run my program the scanf line is run before anything else even though it's nearly at the end.

Code:

printf("Welcome to DigiCam - Made by group 14, Andreas Hussing & Lars Holdgaard\n");
printf("Please specify what you want:\n");
writemenu();

int opt = 0;
scanf("%d",&opt);
printf("\nOption chosen: %d\n\n", opt);

I'm sure it's something quite basic I've misunderstood about the function, because when I Google my problem, I can't seem to find anyone else having this problem...

Thanks!
Can't wait to be able to help others with C too :-)

It seems scanf is getting called first ..could you post the whole code.. I mean your main function and when you are calling writemenu() function as well! .

Originally Posted by Elysia

Why do you think that?

Because I ran the program and that was what happened! ;-)

Here's my code:

Code:

/********************************************************************************
 * Test (main)
 ********************************************************************************/

#include "ccd.h"
#include "lcd.h"

void writemenu()
{
	printf("Press 1 'PATH' to load an image\n");
	printf("Press 2 'FILTEROPTION' to filter an image\n");
	printf("Press 3 'PATH' to save an image\n ");
}

void performOption(int opt)
{
}

int main(int argc, char *argv[]) {
	printf("Welcome to DigiCam - Made by group 14, Andreas Hussing & Lars Holdgaard\n");
	printf("Please specify what you want:\n");
	writemenu();

	int opt = 0;
	scanf("%d",&opt);
	printf("\nOption chosen: %d\n\n", opt);
	performOption(opt);

                return 0;
}

Most likely an orphaned newline being generated somewhere within 'writemenu', causing scanf to skip the input. Check out the FAQ on flushing the input buffer. If that doesn't help, I would suggest posting a complete example that demonstrates the problem.

Originally Posted by Mcoroklo

Because I ran the program and that was what happened! ;-)

Here's my code:

Code:

/********************************************************************************
 * Test (main)
 ********************************************************************************/

#include "ccd.h"
#include "lcd.h"

void writemenu()
{
    printf("Press 1 'PATH' to load an image\n");
    printf("Press 2 'FILTEROPTION' to filter an image\n");
    printf("Press 3 'PATH' to save an image\n ");
}

void performOption(int opt)
{
}

int main(int argc, char *argv[]) {
    printf("Welcome to DigiCam - Made by group 14, Andreas Hussing & Lars Holdgaard\n");
    printf("Please specify what you want:\n");
    writemenu();

    int opt = 0;
    scanf("%d",&opt);
    printf("\nOption chosen: %d\n\n", opt);
    performOption(opt);

                return 0;
}

Sorry, I may have misunderstood your question. Some wonky compilers don't flush the output buffer correctly, in which case you might need to add a fflush( stdout ) after the print statements...