Thread: Stuck on clearing the input buffer

I'm using the while((c = getchar()) != '\n' && c != EOF); method but if it's called, it goes into an infinite loop.

If the character array goes over 10, including '\n', it gets stuck in an infinite loop.

Here's the code in totality:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


static void clearInputBuffer() {
    short int clear;
    
    while((clear = getchar()) != '\n' && clear != EOF);
    
    return;
}


static int nonIntDetector(char *input, unsigned int stringLength) {
    short int inputCounter, intCounter, nonIntDetect, intDetect;
    char Numbers[10] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
    
    nonIntDetect = 0;
    intDetect = 0;
    
    for(inputCounter = 0; inputCounter < stringLength; inputCounter++)
        for(intCounter = 0; intCounter < 10; intCounter++) {
            if(input[inputCounter] == Numbers[intCounter]) {
                intDetect++;
                break;
            }
            if(intDetect != inputCounter) {
                nonIntDetect = 1;
                
                puts("Numbers only, please.");
                
                goto nestedLoopBreak;
            }
    }
    nestedLoopBreak:
    
    return nonIntDetect;
}


int main() {
    short int playAgain, loopChecker, randomNumber, intInput;
    char userInput[64], anotherGame[16];
    
    loopChecker = 1;
    
    puts("Random number guessing game.");
    
    do {
        randomNumber = arc4random_uniform(101);
        do {
            do {
                printf("Enter your guess: ");
                fgets(userInput, sizeof(userInput), stdin);
                
                if(strlen(userInput) > 10) {
                    
                    clearInputBuffer();
                    
                    continue;
                }
            }
            while(nonIntDetector(userInput, strlen(userInput)));
        
            intInput = atoi(userInput);
        
            if(intInput > randomNumber)
                puts("Too High.");
            
            else if(intInput < randomNumber)
                puts("Too low.");
        }
        while(intInput != randomNumber);
    
        puts("You win!");
        
        do {
            do {
                puts("Another game?");
                puts("1. Yes, 2. No");
        
                fgets(anotherGame, sizeof(anotherGame), stdin);
            }
            while(nonIntDetector(anotherGame, strlen(anotherGame)));
        
            playAgain = atoi(anotherGame);
        
            if(playAgain == 2) {
                playAgain = 0;
                loopChecker = 0;
                continue;
            }
            else if(playAgain == 1)
                loopChecker = 0;
        }
        while(loopChecker && puts("Invalid option."));
    }
    while(playAgain == 1);
    
    return 0;
}

Code:

char userInput[64]

// ...

fgets(userInput, sizeof(userInput), stdin);

if(strlen(userInput) > 10) {
    // ...

If the second argument to fgets was 10, and the user entered more characters than this, the rest of the input would remain on the buffer and have to be removed. This seems to be what you're expecting.

However, you're telling fgets to read up to 63 characters, so as long as you enter less than this, there's no need to clear the input buffer. What you're experiencing is not an infinite loop, but the "while" loop in "clearInputBuffer()" waiting for another newline since the previous one has already been read.

My suggesting would be to create your own "get string" function, and to use something like "strchr" in conjunction with "fgets" to remove the newline, if present - if the newline is not present (which likely means there is more input waiting), you can take further action as necessary.

I'll have to give that a shot.

IIRC, if you use fgets and stdin goes over the fgets buffer, the excess characters stay in stdin and are read when another call to fgets is executed.

That's why I'm attempting to clear the buffer. I actually only want a 16 (including \n) buffer.

Also, I know using goto is frowned upon but I've read where situations like nested loops are acceptable.

Like this:

Originally Posted by ImageJPEG

IIRC, if you use fgets and stdin goes over the fgets buffer, the excess characters stay in stdin and are read when another call to fgets is executed.

Yes, or any other input command.

Originally Posted by ImageJPEG

That's why I'm attempting to clear the buffer. I actually only want a 16 (including \n) buffer.

Then that's the size you need to pass to fgets. As it stands, you're giving it sizeof(userInput) which is 64.

Originally Posted by ImageJPEG

Also, I know using goto is frowned upon but I've read where situations like nested loops are acceptable.

That can be argued, yes, but in many cases you can avoid using goto by carefully planning and restructuring your logic to avoid heavily nested loops.

Wow, I feel really dumb not using return 1 :/

Also, so I don't have to keep posting my modified code:

GitHub - e14tech/number_guess: A random number guessing game