(a) before modification
 (1) A
  (2) B
  (3) line will be changed 1
  (4) line will be changed 2
  (5) C
  (6) D
  (7) line will be deleted 1
  (8) line will be deleted 2
  (9) E
  (10) F
  (11) G
  (12) H
(b) after modification
  (1) A
  (2) B
  (3) line changed 1
  (4) line changed 2
  (5) C
  (6) D
  (7) E
  (8) F
  (9) G
  (10) line added 1
  (11) line added 2
  (12) H
(c) diff output
3,4c3,4
< line will be changed 1
< line will be changed 2
---
>line changed 1
>line changed 2
7,8d6
<line will be deleted 1
<line will be deleted 2
11a10,11
>line added 1
>line added 2
Algorithm 1: A simple example of comparing two source files with diff (changed region is represented with identifier “c” like 3,4c3,4; deleted region is represented with identifier “d” like 7,8d6, added region is represented with identifier “a” like 11a10,11). The number before and after the identifier shows the correspond lines.