Operator precedence in Rust - Step-by-Step Execution

Concept Flow - Operator precedence

Start Expression

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Identify Operators

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Check Precedence

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Evaluate Higher Precedence

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Replace Result

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Evaluate Next Operator

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Final Result

The program reads an expression, identifies operators, evaluates them in order of precedence from highest to lowest, and combines results step-by-step until the final value is computed.

Execution Sample

Rust

let result = 2 + 3 * 4 - 5 / 5;
println!("{}", result);

Calculates the expression 2 + 3 * 4 - 5 / 5 following Rust's operator precedence rules.

Execution Table

Step	Expression	Operation	Precedence	Result	Explanation
1	2 + 3 * 4 - 5 / 5	3 * 4	Multiplication (High)	12	Multiply 3 and 4 first
2	2 + 12 - 5 / 5	5 / 5	Division (High)	1	Divide 5 by 5 next
3	2 + 12 - 1	2 + 12	Addition (Lower)	14	Add 2 and 12
4	14 - 1	14 - 1	Subtraction (Lower)	13	Subtract 1 from 14
5	13	None	None	13	Final result after all operations

💡 All operators evaluated in precedence order; final result is 13

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
result	undefined	2 + 12 - 5 / 5	2 + 12 - 1	14 - 1	13	13

Key Moments - 3 Insights

Why is multiplication done before addition in the expression?

Because multiplication has higher precedence than addition, as shown in execution_table steps 1 and 3 where multiplication is evaluated first.

Why does division happen before subtraction?

Division has higher precedence than subtraction, so it is evaluated earlier as seen in execution_table step 2 before subtraction in step 4.

What happens if we ignore operator precedence and evaluate left to right?

The result would be different and incorrect; operator precedence ensures correct order, as shown by the stepwise evaluation in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result after step 2?

A 2 + 12 - 1

B 2 + 3 * 4 - 1

C 14 - 1

D 13

💡 Hint

Check the 'Expression' column in execution_table row for step 2

At which step is the addition operation evaluated?

A Step 1

B Step 3

C Step 4

D Step 2

💡 Hint

Look at the 'Operation' column in execution_table to find when '2 + 12' is calculated

If the division operator had lower precedence than subtraction, which step would change?

A Step 4

B Step 3

C Step 2

D Step 1

💡 Hint

Consider when division is evaluated in execution_table and how precedence affects order

Concept Snapshot

Operator precedence determines the order in which parts of an expression are calculated.
Higher precedence operators like * and / are done before + and -.
Rust follows standard math precedence rules.
Evaluate operators from highest to lowest precedence step-by-step.
Parentheses can override precedence to group operations.

Full Transcript

This example shows how Rust evaluates the expression 2 + 3 * 4 - 5 / 5 by following operator precedence rules. Multiplication and division have higher precedence than addition and subtraction, so 3 * 4 and 5 / 5 are calculated first, resulting in 12 and 1 respectively. Then addition and subtraction are performed left to right: 2 + 12 equals 14, and 14 - 1 equals 13. The final result printed is 13. This stepwise evaluation ensures correct calculation order and result.