If–else expression in Rust - Step-by-Step Execution

Concept Flow - If–else expression

Evaluate condition

↓

Condition true?

No→Execute else block

↓

Use else result

↓

Execute if block

↓

Use if result

↓

Continue with result

The program checks a condition. If true, it runs the 'if' block and uses its result. Otherwise, it runs the 'else' block and uses that result.

Execution Sample

Rust

let number = 7;
let result = if number % 2 == 0 {
    "even"
} else {
    "odd"
};
println!("{} is {}", number, result);

This code checks if 'number' is even or odd and stores the string result, then prints it.

Execution Table

Step	Action	Condition	Condition Result	Block Executed	Result Value
1	Evaluate condition number % 2 == 0	7 % 2 == 0	false	else	"odd"
2	Assign result variable	N/A	N/A	N/A	"odd"
3	Print output	N/A	N/A	N/A	7 is odd

💡 Condition is false, so else block runs; program prints '7 is odd' and ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
number	7	7	7	7
result	uninitialized	uninitialized	"odd"	"odd"

Key Moments - 2 Insights

Why does the else block run even though the condition uses '=='?

Because the condition '7 % 2 == 0' evaluates to false (7 divided by 2 leaves remainder 1), so the else block runs as shown in execution_table step 1.

Is the if–else expression itself a value?

Yes, the if–else expression returns a value from either block, which is assigned to 'result' as shown in execution_table step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'result' after step 2?

A "even"

B "odd"

C 7

D uninitialized

💡 Hint

Check the 'Result Value' column in execution_table row for step 2.

At which step does the program decide which block to execute?

A Step 1

B Step 3

C Step 2

D After printing

💡 Hint

Look at the 'Condition Result' and 'Block Executed' columns in execution_table.

If 'number' was 8 instead of 7, what would 'result' be after step 2?

A "odd"

B 8

C "even"

D uninitialized

💡 Hint

Think about the condition 'number % 2 == 0' when number is 8, and check execution_table logic.

Concept Snapshot

If–else expression in Rust:
let result = if condition {
    value_if_true
} else {
    value_if_false
};
It evaluates condition, runs one block, and returns its value.
Useful for choosing values based on conditions.

Full Transcript

This Rust code uses an if–else expression to check if a number is even or odd. It evaluates the condition 'number % 2 == 0'. If true, it returns "even"; otherwise, it returns "odd". The returned value is stored in 'result'. Finally, it prints the number and whether it is even or odd. The execution table shows the condition evaluation, block chosen, and final output. Variables 'number' and 'result' change as the program runs. This example helps understand how if–else expressions return values in Rust.