How it works
The conditional AND and OR operators evaluate their right operand only when it can change the answer. With AND, a false left side already decides the result. With OR, a true left side already decides it. This evaluation rule lets a condition establish a prerequisite before using a value that depends on it.
A guard should read in dependency order: first confirm that a value exists, then inspect its properties. The rule is about whether an expression executes, not merely about its final truth value. Function calls on the right side can have visible effects, which is one reason to keep validation expressions simple. Parentheses make a mixed condition easier to review even when you know the language precedence rules.
Walk through the example. The first expression checks for null before reading Length, so no property access occurs for a missing value. The second uses OR to select a default path when text is missing or too short. The Probe function increments a counter. Because the left operand is false, the AND expression skips Probe and the counter stays at zero.
Watch the boundary. The single-character boolean operators also accept bool operands, but they evaluate both operands. Replacing a conditional operator mechanically can therefore introduce a null access or an unexpected side effect. A logically equivalent truth table does not guarantee equivalent execution. Avoid embedding updates, logging decisions, or important business actions inside the operands of a validation condition.
Practice independently. Build a password-length check with separate variables for missing text, minimum length, and an optional upper bound. Exercise null, an empty string, a short string, and a valid string. Next add a counter to a checking function and prove which inputs call it. Explain why moving that call to the left side changes the observation even if the final answer stays false.
A working example
using System;
using System.Collections.Generic;
using System.Linq;
using System.Globalization;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.RegularExpressions;
string? text = null;
Console.WriteLine(text != null && text.Length >= 3);
Console.WriteLine(text == null || text.Length < 3);
int calls = 0;
bool Probe() { calls++; return true; }
Console.WriteLine(false && Probe());
Console.WriteLine(calls);
Expected output
False True False 0
Put prerequisites on the left of &&, and keep side effects out of guards.