# Cast to string transform function
## Introduction
The **cast to string** transform function is used to change the data type associated with a source field from `number` to `string`. For example, you might have an `id` field in a source system that's stored as `string` value, but your destination system expects the `id` to be a `number`.
## Adding a cast to string transform
**Step 1**\
In your process flow, access settings for your map shape:
**Step 2**\
Select the **add transform** button for the required mapping rule - for example:
**Step 3**\
Click the **add transform** button:
**Step 4**\
Click in the **name** field to access a list of all available transform functions, then select **cast to string** from the **number** category:
**Step 5**\
Click the **add field** button:
**Step 6**\
Click in **source fields** and select the source field to be used for this transform:
**Step 7**\
Accept your changes (twice).
**Step 8**\
Save the transform. You'll notice that the transform icon is updated to indicate that a transform function is present for the mapping row - for example:
