====== Conditional Flowcharts – if, yes, no ======
The Advanced level adds three flowchart modules that let a flowchart run its job only when a file exists, or only when it does not. They work with the Intermediate flowchart modules; see [[intermediate_level:batch_processing_with_flowcharts|Batch Processing with Flowcharts]].

^ Module ^ What it does ^
| if | Tests whether the file in question exists in the current folder, and passes on the directory and file name with a "yes" or "no" conditional message |
| yes | Must follow if. Tells exec to run its job if the file exists, and not to run it if the file does not exist |
| no | Must follow if. Tells exec to run its job if the file does **not** exist, and not to run it if it does |

exec runs its job when it receives an "exec=yes" message, or no condition at all. It skips the job when it receives "exec=no".

Since Hoku 3.1, "if" has an editor, like exec and mkdir, to help you write its instruction. For details of the instruction, use the **Help** button in its argument dialog.

===== Example: skip images already processed =====
To process only images that do not have an output file yet, test for the output file with **if**, follow it with **no**, and then **exec**. The job then runs only for the images whose output file does not exist.