Let the cost of the piece of bubble gum be \( x \) cents. Then, since the candy bar costs a dollar more than the bubble gum, the cost of the candy bar would be \( x + 100 \) cents.
According to the problem, the total cost of the candy bar and the bubble gum is 200 cents. We can express this with the following equation:
\[ x + (x + 100) = 200 \]
Now, simplify the equation:
\[ 2x + 100 = 200 \]
Next, subtract 100 from both sides:
\[ 2x = 100 \]
Now, divide by 2:
\[ x = 50 \]
Thus, the cost of the piece of bubble gum is \( x = 50 \) cents.
To verify, if the bubble gum costs 50 cents, then the candy bar costs:
\[ 50 + 100 = 150 \text{ cents} \]
Adding these together gives:
\[ 50 + 150 = 200 \text{ cents} \]
This is consistent with the given total of $2.00. Therefore, the cost of the piece of bubble gum is
\[ \boxed{50} \text{ cents}. \]