Sure! Here's a test case generator for the "Sum of Decimal Digits" problem statement:

```python
import random

def tcgen():
    # Number of datasets
    num_datasets = random.randint(1, 100)
    datasets = []
    
    for _ in range(num_datasets):
        # Generate a, b, and n within the specified constraints
        a = random.randint(1, 1000)
        b = random.randint(1, 10000)
        n = random.randint(1, 100)
        datasets.append((a, b, n))
    
    return datasets

# Example usage:
datasets = tcgen()
for dataset in datasets:
    print(dataset)
```

This will generate up to 100 datasets, each consisting of three integers \(a\), \(b\), and \(n\) within the specified constraints.

### Example Output:
```text
(123, 4567, 89)
(999, 10000, 10)
(1, 2, 50)
...
```

### Explanation:
- The function `tcgen` starts by determining a random number of datasets (between 1 and 100).
- For each dataset, it generates random values for \(a\), \(b\), and \(n\) within their respective constraints.
- The generated datasets are stored in a list and returned at the end of the function.
- The example usage shows how you can call `tcgen` to generate the datasets and print them out. Each tuple represents a single dataset.

You can modify or extend the generator as needed to include more specific cases or constraints.