C question

[Thomas White]

Hello,
I have a C question(I know, what am I doing asking this on javaranch :roll: ) but anyways... The following code is supposed to
read 20 numbers from the console and store them in an int array. However, after the 20th number is read, I get a seg fault. As far as I can see, I'm not writing beyond the array size. What am I doing wrong?
code:

#include <stdio.h>
#define SIZE 20
int main()
{
  int i, j,vals[SIZE];
  int printflag;
  for(i = 0; i < SIZE; i++)
  {
    printf("Enter a value between 10 and 100: ");
    scanf("%d",&vals[i]);        
  }
  
  printf("****Printing all values that do not have duplicates****");
  for(i = 0; i < 5; i++)
  {
    printflag = 1;
    for(j += i; j < 5; j++)
      if(vals[j] == vals[i])
      {
        printflag = 0;
        break;
      }
    if(printflag == 1)
      printf("%d",vals[i]);
  }
}
  

Tom
[ July 25, 2003: Message edited by: Thomas White ]

[Ernest Friedman-Hill]

Well, I don't quite understand the logic of the compare-and-print part; in particular, I don't understand the initializer of the inner loop, the j += i part. The variable j is never really initialized. The first j+=i executes when j contains random stack garbage. So here's one possibility: j is negative. The j+=i gives the same negative number (i is 0) and so you access a value before the beginning of the array; this could be an illegal address, giving you the seg fault.

[Thomas White]

Ernest,
Thanks for pointing that out. I meant to write j = i + 1. Now its working.
Thanks again.
Thomas

[Gregg Bolinger]

Thomas, just an FYI, a good place for C questions - http://forums.embeddedthought.com