C Program for class: Passing struct array giving strange result

Question

I have set up a couple of printf statements to find the problem and I am still clueless.

Basically I am creating the array plane to contain 12 struct seats.

Then I assign each struct inside of plane data. Everything looks good at this point.

Then I pass that array to numberEmptySeats and all of the sudden plane[0].seatID is lost in the sauce instead of being the 1 it was originally assigned.

Please help me understand why this is happening.

-------------Current Output-------------

1
Entering numberEmptySeats
1123456789101112
Seats Available: 12

------------Desired Output-------------

1
Entering numberEmptySeats
1
Seats Available: 12

Code:

#include<stdio.h>
#include<string.h>
#define SEATS 12

struct seat {
    int seatID;
    int reserved;
    char firstName[20];
    char lastName[20];
};

void resetPlane(struct seat ar[],int seats);
void numberEmptySeats(struct seat ar[],int seats);

int main()
{
    struct seat plane[SEATS];
    resetPlane(plane,SEATS);
    printf("%d\n",plane[0].seatID);
    numberEmptySeats(plane,SEATS);
}

void resetPlane(struct seat ar[],int seats)
{
    int i;
    for(i=0;i<seats;i++)
    {
        ar[i].seatID = i+1;
        ar[i].reserved = 0; 
        strcpy(ar[i].firstName,"Unassigned");
        strcpy(ar[i].lastName,"Unassigned");
    }
}

void numberEmptySeats(struct seat ar[],int seats)
{
    int i,j=0;
    printf("Entering numberEmptySeats\n");
    printf("%d",ar[0].seatID);
    for(i=0;i<seats;i++)
    {
        if (ar[i].reserved == 0)
        {
            printf("%d",ar[i].seatID);
            j++;
        }
    }
    printf("\nSeats Available: %d\n",j);
}

Paul Roub · Accepted Answer · 2014-11-13 20:06:34Z

3

You're printing the id of every available seat, with no newline afterwards, after printing the first ID once (also without a newline).

void numberEmptySeats(struct seat ar[],int seats)
{
  int i,j=0;
  printf("Entering numberEmptySeats\n");
  printf("%d\n",ar[0].seatID);   // added newline
  for(i=0;i<seats;i++)
  {
    if (ar[i].reserved == 0)
    {
        // printf("%d",ar[i].seatID);     // drop the extra output
        j++;
    }
  }
  printf("\nSeats Available: %d\n",j);
}

answered Nov 13, 2014 at 20:06

Paul Roub

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5 Comments

Jonathan Leffler Over a year ago

Or include a blank or a newline in the printf() to make it clearer.

Matt Over a year ago

Wow, thank you for that, unfortunately the problem I am having is still happening in my main code. I ported this over and I guess it stopped it somehow. This sucks, but thank you for the answer!

Matt Over a year ago

I finally figured out why I was having a problem. char selection[1] = "z"; scanf("%s",selection); I changed the 1 to a 2 and no more problems. Could you please help me understand why?

Paul Roub Over a year ago

A char[] array of length 1 won't have room for the terminating \0 at the end of the string. scanf() doesn't know that, and writes (at least) 2 characters anyway, probably overwriting a nearby variable.

Matt Over a year ago

Makes sense, I really appreciate all the help!

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