1, Boolean value: The most typical conditional expression is Boolean value, that is, true or false. In most programming languages, conditional expressions can directly use Boolean values. Such as if (true) or if (false).
2. Comparison expression: A comparison expression is used to compare whether two values are equal. For example, if(a==b) will check whether variables A and B are equal. If not, the expression returns false；; Otherwise return true. Similarly, if(a=b) checks whether they are not equal.
3. Logical operators: Many programming languages support logical operators (such as AND, or, NOT), which can combine or modify Boolean values. For example, if(a==bANDc==d) will check whether A equals B and C equals D. ..
4. Function call: A conditional expression can also be a function call that returns a Boolean value. For example, in Python, you can call a function and check its return value, such as if my_function(a, b).
How to judge whether the expression is correct?
1. Syntax check: first, check whether the syntax of the expression conforms to the specification. For example, check whether brackets are paired, whether operators are used correctly, whether identifiers are legal, and so on. This step can be done by using the grammar checker of the programming language or by manual checking.
2. Semantic check: on the premise of correct grammar, further check whether the semantics of the expression are correct. For example, for a mathematical expression, it is necessary to check whether the operation order, operands in parentheses and operators are used correctly. For function call, it is necessary to check whether the type and number of parameters are consistent with the function definition.
3. Logic check: If there is nothing wrong with the grammar and semantics of the expression, it is necessary to check its logic. For example, for a conditional statement, it is necessary to check whether the conditional expression can produce true or false values. For loop statements, you need to check whether the loop condition can terminate the loop.
4. Test verification: Finally, the correctness of the expression is verified by inputting some test cases. By inputting different data, observe whether the output result of the expression meets the expectation. If the test case covers all possible situations of the expression, it can be considered that the correctness of the expression has been verified.