Unwanted multiple menu prints in a while loop program in C [duplicate] - c

Question

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scanf() leaves the newline character in the buffer
(7 answers)
Closed 5 years ago.
C beginner here and I'm trying to learn to write a menu program. Below is my code
//A test file to test functions
#include <stdio.h>
#include <stdlib.h>
int enterChangeChar();
void printMenu();
char C = ' ';
int main()
{
char inputVal;
while (1)
{
printMenu();
scanf("%c", &inputVal);
switch (inputVal)
{
case 'c': enterChangeChar(); break;
case 'q': exit(0);
}
}
return 0;
}
int enterChangeChar()
{
int input;
printf("Would you like to Enter or Change the Character value?\n\n");
printf("Enter 1 to Assign OR 2 to Change the value of C: \n");
scanf("%d", &input); //input a integer value
if(input == 1)
{
printf("Enter a character: \n");
scanf(" %c", &C);
printf("You entered: %c", C);
}
else if (input == 2)
{
printf("Change Value option selected\n");
}
return 0;
}
void printMenu()
{
printf("Select a menu choice from the options below: \n\n");
printf(" OPTIONS INPUT\n");
printf("Enter/Change Character 'c'\n");
printf("Quit Program 'q'\n\n");
printf("Enter your CHOICE:\n");
}
when I run the program. The menu is printed twice after I input a character. Why is the program doing so?
Select a menu choice from the options below:
OPTIONS INPUT
Enter/Change Character 'c'
Quit Program 'q'
Enter your CHOICE:
c
Would you like to Enter or Change the Character value?
Enter 1 to Assign OR 2 to Change the value of C:
1
Enter a character:
v
You entered: v
Select a menu choice from the options below:
OPTIONS INPUT
Enter/Change Character 'c'
Quit Program 'q'
Enter your CHOICE:
Select a menu choice from the options below:
OPTIONS INPUT
Enter/Change Character 'c'
Quit Program 'q'
Enter your CHOICE:
q
EDIT: just added the printMenu() function code which I missed out earlier.
Edit 2: Maybe my question is not clear enough. The problem is not with getchar and scanf. The problem is that the menu prints twice after user inputs a character even though it's only called once in the whole program.
Edit 3: Final Edit: Guys I got it now. \n was in the input buffer and whenever choice was given, it was counted as input so the menu was printed multiple times. Thanks for the help.

Answer 1

There are unused newline characters '\n' in your input stream that need to be drained.
scanf() often causes confusion because it will leave the trailing '\n' in the input stream. In your case, the newline is getting picked up by the subsequent getchar().
int main()
{
while (1)
{
char inputVal;
printMenu();
do {
inputVal = getchar();
} while (inputVal == '\n');
switch (inputVal)
{
case 'c': enterChangeChar(); break;
case 'q': exit(0);
}
}
return 0;
}