A statement performs an action or controls execution without returning a usable value. Statement-oriented code commonly combines branching, assignments, and side effects, making missing cases or incorrect assignments easy to overlook. section 4.1.2 section 4.1
Statements differ from expressions in several practical ways:
- They never return a value; their effects come from changing state or calling external systems. section 4.3 section 4.1
- Their branches are treated as separate execution paths, so the compiler may not recognize that every branch should produce related data. section 4.1.3
- They can require default values and repeated assignments, leaving room for missing cases, wrong-variable assignments, and null results. section 4.1.2
Replacing branch assignments with a result
A statement-oriented age description initializes a variable, assigns it in selected branches, and prints whatever remains. An expression-oriented version makes each branch return a string: if age < 18 then "Child" elif age < 65 then "Adult" else "OAP". The result is assigned once, so the catch-all case and the intended destination are explicit. section 4.1.2 section 4.1.4
Listing 4.1 Working in a statement-oriented language
using System;
public void DescribeAge(int age)
{
string ageDescription = null; #1
var greeting = "Hello"; #2
if (age < 18)
ageDescription = "Child"; #3
else if (age < 65)
greeting = "Adult"; #4
Console.WriteLine($"{greeting}! You are a '{ageDescription}'.");
}
Inspect the age-description example to see how initialization, conditional assignments, and output combine into a statement-oriented flow. section 4.1.2
