Thread: Extra loop being executed in do-while loop.

Code:

#include <stdio.h>
#include<ctype.h>

void try5t(){
    
    char choice;
    int choiceint;
    
    do{
        
    printf("1.\tZoo\n2.\tMall\n3.\tExit\n\n");
    printf("Choose a place by entering its numerical value: ");
    scanf("%c", &choice);
    
    choiceint = choice - '0';
    //DEBUG
    printf("\nchoiceint is %d\n",choiceint);
    
        if(!isdigit(choice) && choiceint > 3){
            printf("You did not enter an accepted digit.\n");
        }
        else if(choiceint != 3){
            switch(choiceint){
                    case 1:
                        printf("You chose the Zoo.\n");
                        break;
                    case 2:
                        printf("You chose the Mall.\n");
                        break;
            }// end of switch
        }// end of else if
            else{
            
            }// end of else
    
        }// end of do 
    while(choiceint !=3);
     
}

Loop is repeated an additional time as shown in the screenshot:

FAQ > How do I avoid a "dangling" newline when reading single character user input? - Cprogramming.com

Originally Posted by Matticus

FAQ > How do I avoid a "dangling" newline when reading single character user input? - Cprogramming.com

Great link, I've read the 2nd part about flushing the buffer. The author raised an important point, what if the user entered more than 1 character, the program will fail. So, flushing the buffer will solve this issue too.

However, the code snippet provided is kinda lengthy and I am trying to code a simple while loop to remove any number of characters after the first character.

This is what I've done :

Code:

printf("1.\tZoo\n2.\tMall\n3.\tExit\n\n");     
printf("Choose a place by entering its numerical value: ");     
scanf("%c", &choice);

// code to "eat up" all chars after the first char
    while(choice !='\n'){
       scanf("%c", &rejectedChar);
    }

Sadly, it doesn't work, the while loop seems to be stuck in an infinite loop as the program fails to exit out of the input stream.

Sadly, it doesn't work, the while loop seems to be stuck in an infinite loop as the program fails to exit out of the input stream.

choice is used to control the loop, but never modified within the loop body. Here is a function you can use to flush stdin up to the next line break:

Code:

void flush_line(void)
    {
    if (!feof(stdin) && !ferror(stdin))
        {
        int c;

        while ((c = getchar()) != '\n' && c != EOF)
            {
            /* noop */
            }

        /* Clear EOF but leave stream errors */
        if (feof(stdin))
            {
            clearerr(stdin);
            }
        }
    }

Can't you just do this to get up to the newline :

Code:

fscanf( stdin, "%1c[^\n]", &your_variable_name );

That would be more complex, but it would save you a lot of code.

Can't you just do this to get up to the newline

Getting up to the newline isn't the issue - it's getting rid of that newline (and any extra characters preceding it) as to not interfere with later code that reads from stdin.

Code:

#include <stdio.h>

int main(void)
{
    char input1;
    char input2;

    printf("Enter character for input1:\n");
    fscanf( stdin, "%1c[^\n]", &input1 );    /* your proposed solution */
    printf("Enter character for input2:\n");
    fscanf( stdin, "%1c[^\n]", &input2 );    /* your proposed solution */

    printf("input1 character = %c\n",input1);
    printf("input2 character = %c\n",input2);

    if(input2 == '\n')
        printf("\nSecond character is a newline\n");

    return 0;
}

/*
Enter character for input1:
a
Enter character for input2:
b
input1 character = a
input2 character =


Second character is a newline

*/