Thread: Scanf() skipped

This is my program code for the main.c

Code:

#include <stdio.h>
#include <stdlib.h>
#include "test.h"

int main()
{
    float a,b,c;
    int s,g=1;
    char ch;
while(g)
{
    printf("\nArea of:\n1.Triangle\n2.Square\n3.Circle\n4.Convert letter\nplease choose:");
    scanf("%d",&s);

    switch(s)
    {
        case 1:
        printf("\nlength:");
        scanf("%f",&a);
        printf("width:");
        scanf("%f",&b);
        c=TRI(a,b);
        printf("The area is %f",c);
        break;
        case 2:
        printf("\nlength:");
        scanf("%f",&a);
        printf("width:");
        scanf("%f",&b);
        c=SQU(a,b);
        printf("The area is %f",c);
        break;
        case 3:
        printf("\ndiameter:");
        scanf("%f",&a);
        c=CIR(a);
        printf("The area is %f",c);
        break;
        case 4:
        printf("Upper Case Letter");
        scanf("%c",&ch);
        ch=CONV(ch);
        printf("\nLower Case Version: %c",ch);
        break;
        default:
        printf("YOU PICKED WRONG NUMBER\n");
        continue;
    }
    printf("\ndo you want to use the program again(1=yes/0=no)?");
    scanf("%d",&g);
}
return 0;

}

and this is for "test.h"

Code:

#ifndef test_h
#define test_h

#define TRI(a,t) (0.5*a*t)
#define SQU(p,l) (p*l)
#define CIR(r) (0.25*3.14*r*r)
#define CONV(c) (c+32)

#endif

when i compile it, there isn't any warning or error.
but when i run the program, i choose menu 4(Convert Letter),the program skipped the scanf(), so i didn't have the chance to input the letter.
can someone help me please?i don't know what's wrong with my code

*note:don't mind with the Macro abuse. it's just an exercise.

Well, I haven't gone through your code, but most scanf skipping problems are related to the input buffer not being flushed. Heres what I mean -

Cprogramming.com FAQ > Flush the input buffer

@spidey: i still don't understand about code and the explanation in the FAQ that you showed to me. sorry, i'm totally a newbie. is there any better way to make me understand it ? but, thnks for your help before.

---------------------------------------------------------------------------------------------------------------

@MK27: getchar doesn't solve the problem.
but, i use your method to input "\n", then the program become messy.

the program run like this

Code:

Area of:
1.Triangle
2.Square
3.Circle
4.Convert Letter
please choose:4
Upper Case Letter:A

Lower Case version: *
do you want to use the program again(1=yes/0=no)?
Area of:
1.Triangle
2.Square
3.Circle
4.Convert Letter
please choose:Upper Case Letter:

the program doesn't wait me to confirm whether i use the program again or not. it directly shows the menu again. and the program also doesn't wait the input for menu selection
and the conversion to low case letter doesn't works.
but,when i input any character after "please choose:Upper Case Letter:". it happened like this:

Code:

Area of:
1.Triangle
2.Square
3.Circle
4.Convert Letter
please choose:4
Upper Case Letter:A

Lower Case version: *
do you want to use the program again(1=yes/0=no)?
Area of:
1.Triangle
2.Square
3.Circle
4.Convert Letter
please choose:Upper Case Letter:B

Lower Case version: a
do you want to use the program again(1=yes/0=no)?
Area of:
1.Triangle
2.Square
3.Circle
4.Convert Letter
please choose:Upper Case Letter:

the conversion works,but it messy.
it makes me feel more confused.
what's going on with the program?

MK got his left and right mixed up -- "%c\n" will read a character (in this case, still the carriage return and then requires another carriage return afterwards (hence the printing of a blank line -- because that's the input) and the weirdness after).

What you want instead is to use " %c" (notice the space between the quote and the % sign) to get rid of carriage-returns before the input.

What Ben10 says, but I would add that you indent a bit within your switch case statement. Your code is all bunched together.

oh,i understand it and the "buffer" things now.
thanks for your (all of you who reply my thread) help.

but, i still don't understand clearly why the "space" in scanf() can eat up the "/n".
i tried to use getchar() (like MK27 said),but i put it before scanf() to fix the ENTER problem, in this case i still understand about what the getchar( ) did.
but nit with the "blank space" in scanf().
how does it work?

but nit with the "blank space" in scanf().
how does it work?

Its basically the same concept as getchar(). But adding a space before the % causes it to skip the space.
Just think of it as if the newline and the space cancel each other out, and then the input is read by scanf.