[c] Random character

[pistilloi]

//rand.c

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

int main()
{
  srand(time(NULL));
  
  unsigned char c; 
  
  c = 'a' + rand() % 'z' ;

  printf("random character: %d %c\n", c, c);

  return 0;
}

$ cc rand.c -o rand
$ ./rand
random character: 187 �
$ ./rand
random character: 114 r
./rand
random character: 114 r
./rand
random character: 169 �
$

Why?