Create SPFieldCalculated using C#

CalculatedField.cs

private void AddCalculatedField(SPList list)
{
    var fieldName = "FieldName";

    // Create field
    string fieldInternalName = list.Fields.Add(fieldName, SPFieldType.Calculated, false);

    // Get field
    SPFieldCalculated calculatedField = list.Fields.GetFieldByInternalName(fieldInternalName) as SPFieldCalculated;

    // Set other properties
    calculatedField.Description = "Calculated Field Description";
    calculatedField.Formula = "=[Title]";
    calculatedField.OutputType = SPFieldType.Text;
    
    // Update field
    calculatedField.Update();
}