What does a 'switch' statement use to determine which code block to execute?

A 'switch' statement is designed to evaluate a single expression and compare it against a series of predefined values or cases to determine which corresponding block of code to execute. This structure enables a clear and efficient way to branch the flow of execution based on the evaluated expression's value.

When the switch statement runs, it evaluates the expression once and then compares the result against each specified case. If a match is found, the program begins executing the code block associated with that case. If no matches are found, a default case can handle any fallback behavior if a case is not satisfied.

In contrast, the other options do not align with the fundamental operation of a switch statement. A variable's data type does not affect the switch's execution flow directly. Conditions set for error handling pertain to try-catch constructs instead of switch statements. Lastly, the output of another function doesn't directly influence which case gets executed in a switch; rather, the function's output would first need to be evaluated and potentially passed into the switch as the expression to be compared.

Understanding the switch statement's mechanism of using a single expression evaluated against multiple values is crucial for effectively implementing control flow in programming.