Unwanted multiple menu prints in a while loop program in C

Question

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.

You have not shown the implementation of `void printMenu();` — Weather Vane, Feb 09 '18 at 22:44
Instead of using `getchar` in `main`, use `scanf` just like you did to read the new value of `C` in `enterChangeChar`. In general, don't mix input functions. If the code uses `scanf` for anything, it should use `scanf` for everything. — user3386109, Feb 09 '18 at 22:46
I forgot to add the last `printMenu()` function on my original post. I've edited it. — tryingToLearnC, Feb 10 '18 at 03:50

Stephen Docy · Accepted Answer · 2018-02-10T00:23:49.883

0

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;
}

edited Feb 10 '18 at 00:23

answered Feb 09 '18 at 22:43

Stephen Docy

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Mixing input methods such as `scanf` with `getchar` can be a problem. The answer would be better as a comment as there is no actual answer given here. – Weather Vane Feb 09 '18 at 22:51
1

Avoid using `"Try"` as it suggests you are unsure your answer is correct and that the OP should try it out and see if it works and report back. – David C. Rankin Feb 10 '18 at 00:20
Thanks, good tip. – Stephen Docy Feb 10 '18 at 00:25
Even after I removed the `getchar` and used `scanf`, the problem is still there. My problem is that after I input a char in my `enterChangeChar` function, the menu is printed twice. I'm not sure why. – tryingToLearnC Feb 10 '18 at 03:58
I got it now. And I understood the explanation now. Thanks – tryingToLearnC Feb 10 '18 at 04:16
Glad to help, good job sticking with it and figuring it out. – Stephen Docy Feb 10 '18 at 04:25

Unwanted multiple menu prints in a while loop program in C

1 Answers1