While-loops keep repeating, Debug error when program stops

Question

I am using Visual Studio 2010. while is keep repeating and I get an error when program stops.

It is just increasing the value of the array 700 times more than it should, and the "line" shows that it's just repeating the while loop more than it should (~700 times more)

Code:

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

#include <time.h>
#include <iostream>

int main(){

     int loop,loop2,loop3,usergirdi,random,linecounter,s,b,x;
     int a[17];
     printf("baslayarak \n");
     scanf("%d",&usergirdi);

     for (loop=1;loop<=16;loop++){
         a[loop]=0; }
     for (loop2=1;loop2<=15;loop2++){
            if(loop2==usergirdi){
                usergirdi=usergirdi;
                a[usergirdi]+=1;
                printf("%d ",a[usergirdi]); }

            else
                printf("%d ",a[loop2]);}

    linecounter=0;

    printf("\n");

while (a[1]<1||a[15]<1||a[2]<1||a[3]<1||a[4]<1||a[5]<1||a[6]<1||a[7]<1||a[8]<1||a[9]<1||a[10]<1||a[11]<1||a[12]<1||a[13]<1||a[14]<1){

linecounter++;

         srand ( time(NULL) );
            random=(rand()%15+1);



     if (a[random-1]==0 && a[random+1]==0 && a[random]==0 ){}

     else if (a[random-1]!=0 || a[random+1]!=0 )
                {
                    a[random]+=1;

     }
    for (b=0;b<=14;b++){
        printf("%d ",a[b]); }
     printf("[line %d]\n",linecounter);



}}

---

Debug error:

Answer 1

Your code is subject to undefined behavior. You are accessing the array using an out of bound index in several places.

1. Before the start of the while loop.

   a[16] = 0;
   

2. Inside the while loop.

   a[16] = 0;
   a[-1] = 0;
   

3. Again inside the while loop

   if (a[random-1]==0 && a[random+1]==0 && a[random]==0 ){}
      // ^^ If random == 0
   

4. Again inside the while loop

   else if (a[random-1]!=0 || a[random+1]!=0 )
           // ^^ If random == 0
   

You can remove those errors by:

1. Using

   a[15] = 0;
   

2. Replacing the line

   a[-1] = 0;
   

   with

   a[0] = 0;
   

3. Changing the line that generates random to:

   random=(rand()%14)+1;
   

The errors in logic can be removed by:

1. Moving the call to srand outside the while loop.

2. Removing the a[0] < 1 check from the while loop's conditional.

Answer 2

a[16]=0;

This array index runs from 0-15 a[16] is array out of bound access and leads to UB.

Get rid of this also :

a[-1]=0;