Expression evaluation in Rust - Step-by-Step Execution

Concept Flow - Expression evaluation

Start

↓

Parse expression

↓

Evaluate operands

↓

Apply operator

↓

Get result

↓

End

The program reads an expression, evaluates each part, applies the operator, and produces the final result.

Execution Sample

Rust

fn main() {
    let result = 3 + 4 * 2;
    println!("{}", result);
}

This code calculates 3 plus 4 times 2 and prints the result.

Execution Table

Step	Action	Evaluation	Result
1	Evaluate 4 * 2	4 * 2	8
2	Evaluate 3 + 8	3 + 8	11
3	Print result	println!("{}", result)	11

💡 Expression fully evaluated and result printed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
result	uninitialized	uninitialized	11	11

Key Moments - 2 Insights

Why is 4 * 2 evaluated before adding 3?

Because multiplication has higher priority than addition, so step 1 evaluates 4 * 2 first as shown in execution_table row 1.

Why does the variable 'result' change only after step 2?

The variable 'result' gets its value after the full expression is evaluated, which happens at step 2 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of the expression after step 1?

A 11

B 6

C 8

D 7

💡 Hint

Check the 'Result' column in execution_table row 1.

At which step is the variable 'result' assigned a value?

A Step 1

B Step 2

C Step 3

D Before Step 1

💡 Hint

Look at variable_tracker row for 'result' and see when it changes from uninitialized.

If the expression was changed to (3 + 4) * 2, what would be the result after step 2?

A 14

B 10

C 11

D 7

💡 Hint

Parentheses change evaluation order; check how execution_table would change.

Concept Snapshot

Expression evaluation in Rust:
- Operators follow precedence (e.g., * before +)
- Evaluate operands first
- Apply operator to operands
- Store result in variable
- Print or use result
Example: let result = 3 + 4 * 2; // result is 11

Full Transcript

This example shows how Rust evaluates an expression step-by-step. First, it calculates 4 times 2, getting 8. Then it adds 3 to 8, resulting in 11. The variable 'result' is assigned this value. Finally, the program prints 11. Multiplication happens before addition because of operator precedence. Changing the expression with parentheses changes the order of evaluation and the final result.