My program skip getting input data? [duplicate] - c

Question

This question already has answers here:
Simple C scanf does not work? [duplicate]
(5 answers)
Closed 9 years ago.
I have written a simple program to exchange currency and able to buy a beer.
But there something in program and I don't know why, it auto skips the third input data -> end program.
Here my code :
#include <stdio.h>
#include <stdlib.h>
int main()
{
int ex_rate_into_vnd = 20000; //! Exchange Rate
int beer = 7000; //! Local price of a beer
float in_c = 0; //! Input amount of money
float out_c = 2; //! Amount of currency to exchange !
float choice; //! Switch mode
char buy; //! Deal or not
//! Introduction
printf ("||---------------------------------------------------||\n");
printf ("|| Currency Exchange Machine beta ||\n");
printf ("||---------------------------------------------------||\n");
printf ("Please choose your option:\n");
printf("\t 1.Exchange VND to dollar\n");
printf("\t 2.Exchange Dollar to VND\n");
do
{
printf("Your choice: ",choice);
scanf("%f",&choice);
} while( choice != 1 && choice != 2);
printf ("Please enter amount of money:");
scanf("%f",&in_c);
if (choice == 1 )
{
out_c = in_c / ex_rate_into_vnd;
printf ("Your amount of money: %.2f",out_c);
}
else
{
out_c = in_c * ex_rate_into_vnd;
printf ("Your amount of money: %.0f",out_c);
}
//! End of Exchanging
printf ("\nWould you like to buy a beer (y/n) ?",buy);
scanf("%c", &buy);
if (buy == 'y')
{
if (out_c >= 7000)
{
out_c = out_c - 7000;
printf("Transactions success !\n");
printf("Your amount: %2.f",out_c);
}
}
printf ("\nWhy Stop ?");
return 0;
}

Answer 1

You have at least one \n between the latest float entry and the char you want to read. You need to get rid of that first.
See also all answers in getchar after scanf category

Answer 2

Change
scanf("%c", &buy);
to
scanf(" %c", &buy);
// ^space
Because the newline character is still in the input buffer after you enter a number and press ENTER in the second scanf.

Answer 3

Instead of scanf("%c", &buy);
1.use space before %c
scanf(" %c",&buy); //space before %c
^
this skips reading of white space (including newlines).
2.or Use getchar(); before scanf("%c", &buy); statement
getchar(); //this hold the newline
scanf("%c", &buy);
3.or use two times getchar();
getchar();
buy=getchar();
//here getchar returns int , it would be better if you declare buy with integer type.
In GCC usage of fflush(stdin); is discouaraged. please avoid using it.

Answer 4

I was wondering why you made 'choice' a float, not an int
Also, consider using a switch-case
that way, you won't have to do the whole do-while loop.
Also, in the line
printf ("\nWould you like to buy a beer (y/n) ?",buy);
Why did u add that?
Here is what I would have done :
printf("Your choice?\n>");
scanf("%d", &choice);
switch(choice)
{
case 1 :
{
out_c = in_c / ex_rate_into_vnd;
printf ("Your amount of money: %.2f",out_c);
}
case 2:
{
out_c = in_c * ex_rate_into_vnd;
printf ("Your amount of money: %.0f",out_c);
}
default :
printf("\nThere has been an error\n"):
reloadprogram(); /* Reloadprogram() is simply to make this go back to the asking thing :) */
}
}
EDIT: also, where it says if( <somevariable> >= 7000), change 7000 to beer, so that way, if u change beer, you won't have to change this :)

Answer 5

Put a fflush(stdin) to clear the input before the last scanf

Answer 6

The program doesn't skip the third input data, it just scans the newline you press after the second input. To fix this, type scanf("%*c%c", &buy); instead of scanf("%c", &buy);. This little %*c scans and ignores the the character read from the input.

Answer 7

you can remove the buy variable from the printf call, it's unneeded
printf ("\nWould you like to buy a beer (y/n) ?",buy);
And replace char buy by char buy[2]; . because a sting is always terminated by /0.
You can also add a memset (buy, 0, sizeof(buy)), to be sure that memory is reset before you start to use it.