Question

I have this code:

int main(){

  char vector[52];
  char i;

  /* initialize the vector */
  for (i ='a'; i < 'z'; i++){
    vector[i] = i - 'a' + 1;
  } 
  // vector is like vector['a'] = 1, vector['b'] = 2 .. vector['z'] = 26


  for (i ='A'; i <= 'Z'; i++){
    vector[i] = i - 'A' + 27;
  }
  // vector is like vector['A'] = 27, vector['B'] = 28 .. vector['z'] = 52

  for (i ='a'; i <= 'z'; i++){
    printf("letter %c : %d \n", i, vector[i]);
  } 

  for (i ='A'; i <= 'Z'; i++){
    printf("letter %c : %d \n", i, vector[i]);
  }

  return 0;
}

Output :

letter a : 1 
letter b : 2 
letter c : 3 
letter d : 4 
letter e : 5 
letter f : 6 
letter g : 7 
letter h : 8 
letter i : 9 
letter j : 10 
letter k : 11 
letter l : 12 
letter m : 13 
letter n : 14 
letter o : 15 
letter p : 16 
letter q : 17 
letter r : 18 
letter s : 19 
letter t : 20 
letter u : 21 
letter v : 22 
letter w : 23 
letter x : 24 
letter y : 25 
letter z : 0 
letter A : 27 
letter B : 28 
letter C : 29 
letter D : 30 
letter E : 31 
letter F : 32 
letter G : 33 
letter H : 34 
letter I : 35 
letter J : 36 
letter K : 37 
letter L : 38 
letter M : 39 
letter N : 40 
letter O : 41 
letter P : 42 
letter Q : 43 
letter R : 44 
letter S : 45 
letter T : 46 
letter U : 47 
letter V : 48 
letter W : 49 
letter X : 50 
letter Y : 51 
letter Z : 52 
*** stack smashing detected ***: ./a.out terminated
======= Backtrace: =========
/lib/i386-linux-gnu/libc.so.6(__fortify_fail+0x50)[0xc25df0]
/lib/i386-linux-gnu/libc.so.6(+0xe5d9a)[0xc25d9a]
./a.out[0x8048547]
[0x343332]
======= Memory map: ========
00110000-0012a000 r-xp 00000000 08:01 131939     /lib/i386-linux-gnu/libgcc_s.so.1
0012a000-0012b000 r--p 00019000 08:01 131939     /lib/i386-linux-gnu/libgcc_s.so.1
0012b000-0012c000 rw-p 0001a000 08:01 131939     /lib/i386-linux-gnu/libgcc_s.so.1
00a19000-00a1a000 r-xp 00000000 00:00 0          [vdso]
00aa4000-00ac0000 r-xp 00000000 08:01 131898     /lib/i386-linux-gnu/ld-2.13.so
00ac0000-00ac1000 r--p 0001b000 08:01 131898     /lib/i386-linux-gnu/ld-2.13.so
00ac1000-00ac2000 rw-p 0001c000 08:01 131898     /lib/i386-linux-gnu/ld-2.13.so
00b40000-00c9a000 r-xp 00000000 08:01 131911     /lib/i386-linux-gnu/libc-2.13.so
00c9a000-00c9b000 ---p 0015a000 08:01 131911     /lib/i386-linux-gnu/libc-2.13.so
00c9b000-00c9d000 r--p 0015a000 08:01 131911     /lib/i386-linux-gnu/libc-2.13.so
00c9d000-00c9e000 rw-p 0015c000 08:01 131911     /lib/i386-linux-gnu/libc-2.13.so
00c9e000-00ca1000 rw-p 00000000 00:00 0 
08048000-08049000 r-xp 00000000 08:01 40062      /home/valter/Documents/Complexidade/recursivo/a.out
08049000-0804a000 r--p 00000000 08:01 40062      /home/valter/Documents/Complexidade/recursivo/a.out
0804a000-0804b000 rw-p 00001000 08:01 40062      /home/valter/Documents/Complexidade/recursivo/a.out
0846f000-08490000 rw-p 00000000 00:00 0          [heap]
b7772000-b7773000 rw-p 00000000 00:00 0 
b7782000-b7785000 rw-p 00000000 00:00 0 
bfa50000-bfa71000 rw-p 00000000 00:00 0          [stack]
Aborted

I don’t understand why is giving this error message.
I should have a vector like this :

vector['a'] = 0, vector['b'] = 1,  .., vector['z'] = 26, vector['A'] = 27, vector['B'] = 28, .., vector['Z'] = 52

I understand that I have this vector but the error came with it.
How solve this problem ?

Answer 1

Because ‘Z’ is not equal to ‘z’.

‘Z’ is equal to 90 and your vector only has 52 elements. Your highest index is 51 so you are basically going out of bounds!

For example when you are doing this

  for (i ='A'; i <= 'Z'; i++)
  {
    vector[i] = i - 'A' + 27;
  }

This is what your first iteration looks like:

vector[65] = 65 - 65 + 27; // <-- Wrong index !