Scan single character C - c

Question

/*
Program to calculate trip and plan flights
*/
#define TRIP 6
#define DEST 1
#include <stdio.h>
int error_dest(int type_num, int cont_num, int dest_code, int check);
int main(void)
{
int check, type_num, cont_num, index, i, dest_code, trip_num, row, col;
int travelint[TRIP][DEST], travelarea[TRIP];
char area_code, S, M, L, N, P, K, R, C, U, W, O;
trip_num = 7;
while (trip_num > TRIP)
{
printf("Please enter the number of trips:");
scanf("%d", &trip_num);
if ( trip_num < TRIP)
{
printf("Valid trip number. Please proceed to enter destination code.\n");
}
else
{
printf("Invalid trips. Please enter no more then 6 trips.\n");
}
}
/*********************************************************************************/
for (i=0; i < trip_num ; i++) /*destination code input*/
{
printf("Please enter destination code:");
scanf("%d", &dest_code); /*input of destination code*/
check = error_dest(type_num, cont_num, dest_code, check);
if (check == 2)
{ travelint[i][0]=dest_code; }
else
{
while (check == 1)
{
printf("Please enter destination code:");
scanf("%d", &dest_code); /*input of destination code*/
check = error_dest(type_num, cont_num, dest_code, check);
if (check == 2)
{ travelint[i][0]=dest_code; }
}
}
printf("Please select from the following that best describes your destination:\n");
printf("S Small city - population under 50,000\n");
printf("M Medium city - population between 50,000 and 500,000\n");
printf("L Large city - pop. over 500,000\n");
printf("N Natural formation like a mountain, a lake, a cave, a geyser, a fjord, a canyon, etc.\n");
printf("P Designated park or reserve such as a wildlife refuge, a national park, a bioreserve, or a protected marine area\n");
printf("K Man made landmark like the Great Wall of China, the Taj Mahal, or Stonehenge\n");
printf("R State or province or region of a country\n");
printf("C Whole country\n");
printf("U Multiple countries like traveling through Europe\n");
printf("W Ocean voyage\n");
printf("O Any other type of destination - such as visiting the sites of the seven wonders of the world\n");
printf("Please enter the Area Letter code:");
scanf("%c", &area_code);
}
/*******************************************************************************/
/*print for destination_code*/
for (row = 0; row < trip_num; row++)
{
for (col=0; col < DEST; col++)
printf("Trip[%d] = %d\n", row+1, travelint[row][col]);
}
return 0;
}
error_dest(type_num, cont_num, dest_code, check)
{
cont_num = dest_code / 10000; /*math for error check*/
type_num = dest_code/1000 - cont_num*10;
if ( (cont_num <= 7) && (cont_num > 0) && (type_num <= 5) && (type_num >=0) )
{ /* loop for checking destination code*/
check = 2 ;
return check;
}
else
{
printf("%d is a invalid code\n", dest_code);
check = 1;
return check;
}
}
for some strange reason at the scanf("%c", &area_code); it just runs ahead and print the dest_code array without letting me input any character and I'm not sure what exactly I am doing wrong.

Answer 1

If you're looking to grab only one character, perhaps it would be better to use getchar() instead of scanf()?

Answer 2

Basically what's happening is this: you print the "Please enter the number of trips" message to the screen. The user types in 4 and then hits the enter key, which means the stdin buffer looks like this: "4\n". You then call scanf with the "%d" format string. scanf looks at the stdin buffer, and sees the 4. It looks at the next character, which is the newline, and sees it's not part of a number (as %d specifies), so it is done fulfilling the format string and leaves the file pointer at the newline. It converts the char '4' to an integer 4 and places it in trip_num and returns.
The next time you call scanf, it picks up where it left off at the newline. The format string this time is "%c", so it just grabs the next character from the buffer which is currently the newline ("\n"), places it in dest_code, and returns. If you want the scanf function to skip over the whitespace in this case, you have to explicitly tell it by adding a space before the "%c" format for the second scanf (destination code). Then scanf will skip over all whitespace (including that newline) until it encounters a non-whitespace character that it places in dest_code.
TL;DR: Change the second scanf call to scanf(" %c", &dest_code). And fix the other errors others have pointed out so other bugs won't manifest.

Answer 3

You may print area_code after scanf, I guess it may be '\n' which is the last character of the dest_code line you entered.

Answer 4

You should empty the buffer before reading a character from stdin:
int c = 0;
while (c != '\n' && c != EOF)
{
c = getchar();
}
then you can read your character using scanf or replace it with getchar.

Answer 5

This may or may not help, but previously stated you probably need to put the getchar() into the while loop. You may also need the fgets to grab the stdin from the keyboard.
while(1){
printf("Enter Message Type:");
fflush(stdout) ;
// scan msg.hdr from received message.
scanf("%d", &(msg.m_hdr));
while(getchar() != '\n'){}
printf("Enter your Message:");
fflush(stdout);
// grab data from keyboard
fgets(msg.m_data, sizeof(msg.m_data), stdin);

Answer 6

Use "fflush(stdin)" before you enter the character, i.e. before the "printf" statement for the character. It will flush out the input buffer and thus you can scan the desired character. Or simply give a Space before the "%c" command. Like---------- scanf(" %c", &area_code); ---------------