Re: another question about entering names in a queue

From:
Victor Bazarov <v.Abazarov@comAcast.net>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 17 Jun 2009 15:47:22 -0400
Message-ID:
<h1bh6j$ndv$1@news.datemas.de>
elodie wrote:

Hi everyone,

I am working on the piece of code below. It is supposed to allow the
user to insert 10 or so names into a queue, and do other operations,
such as deletion of a name, and print the queue.

When I scan several names successively, and then print the queue, the
name I entered first is not printed. The name I entered second is
printed first, and so on. I am not sure if the name I entered first is
not scanned, or not printed, or lost somewhere along the way. I would
appreciate your suggestions on how to identify and solve this issue.

Thanks a lot in advance for your help.

#include <stdio.h>
#include <string.h>
#define MAXNUM 10
#define MAXS 8


My name might fit in 8 chars, but what about those that are longer?

void insertq(void);
void deleteq(void);
void insertq(void);
void printq(void);

char q[MAXNUM][MAXS];
int h, t;
void main(void)


int main(void)

{
    char response[MAXS];

Uninitialized array. Consider

        char response[MAXS] = {0};

     h=-1;
    t=-1;
    printf("i/d/p/q");
    scanf("%s", response);

Extremely dangerous. What if I type more than MAXS-1 characters?

     while (response[0] != 'q' && response[0] != 'Q')
        switch(response[0]){
            case 'i':
                insertq();
                break;
            case 'd':
                deleteq();
                break;
            case 'p':
                printq();
                break;
            default:
                printf("error input i/p/d/q");
                break;
        }
    printf("i/p/d/q");
    scanf("%s", response);
}

void insertq(void)
{
    char response[MAXS];
    if (t-h+1 == MAXNUM)
        printf("overflow \n");
    else{
        printf("enter name");
        scanf("%s", response);
        strcpy(q[++t],response);
        if(h==-1){
            h=0;
            t=-1;

So, you're resetting 't' here? Why?

         }
    }
}

void printq(void)
{
    char response[MAXS];
    int j;
    printf("l or p");
    scanf("%s", response);

    if(response[0]=='l')
        for (j=h; j<=t; j++)
                printf("%d %s \n", j, q[j]);
    if (response[0]=='p')
        for (j=h; j<=MAXNUM; j++)
                printf("%d %s \n", j, q[j]);
}

void deleteq(void)
{
        if(h==-1)
            printf("underflow \n");
        else
            printf("servicing %s \n", q[h++]);
        if(h>t){
            h=-1;
            t=-1;
        }
}


Have you tried stepping through your program at least a couple of times
with a pencil and paper? Or perhaps using the debugger?

V
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