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Doubling the plus sign stops it meaning addition and starts it meaning a change in place.
One plus sign adds two things and produces a result. Two plus signs add one to a variable and store it back, changing the variable itself. The distinction is not addition versus addition-by-one; it is producing a value versus modifying one, and the doubled form is routinely misread as ordinary arithmetic.
Doubling the plus sign changes it from addition to a modification in place, which is routinely misread as addition.
Drawn from the visual attributes recorded for each symbol. Only traits the two records disagree about are listed.
| Trait | Plus sign | Increment operator |
|---|---|---|
| Built from | crosses, lines and dots | crosses |
| Symmetry | bilateral | horizontal |
| Plus sign | Increment operator | |
|---|---|---|
| Number of signs | One | Two |
| What it does | Produces a sum | Adds one and stores it back |
| Changes its operand | No | Yes |
| Position matters | No | Yes — before or after changes what the expression yields |
| Relationship (from Symbolwise's records) | Commonly confused with Increment operator — Doubling the plus sign changes it from addition to a modification in place, which is routinely misread as addition. | Commonly confused with Plus sign — The increment operator is the plus sign doubled, and doubling changes it from addition to a modification in place. |
Unicode Code Chart: Basic Latin (U+0000–U+007F)
The Unicode Consortium · retrieved 2026-07-30
Authoritative for the character's code point, name and block only. Unicode assigns identity; it does not define what a symbol means in use.
Wikipedia · retrieved 2026-07-30
Tertiary reference. Used for widely-agreed identity and origin summary, not for contested detail or exact dates.
ECMA-262, ECMAScript Language Specification
Ecma International · retrieved 2026-08-01
Authoritative for JavaScript's own syntax and only for that. A construct spelled the same way in another language may behave differently, and records say which language they are describing.
Increment and decrement operators
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for widely-agreed identity, origin and current use, not for contested detail or exact dates.
Alpha is a Greek letter and stands for a quantity — an angle, a coefficient, a significance level. The proportionality sign is an operator and stands between two quantities to say they keep a constant ratio. The drawings differ in that the proportionality sign's right-hand stroke runs out in an open curve rather than closing into the letter's tail.
Look at the left-hand edge. A straight flat back is an AND gate: the output is true only when every input is. A curved concave back is an OR gate: true when any input is. Everything else about the shapes is similar, which is why the back edge is worth checking deliberately rather than at a glance.
Look at what follows. A prefix never stands alone — it is glued to a unit symbol, as in kW or kg. A constant stands by itself in an equation. Careful physical writing subscripts the constant as k_B for exactly this reason, and the kelvin's capital K is a third claimant to the same letter.
Length is the tell. A crescendo hairpin is drawn long, below a stave, and spans the passage it applies to — its extent *is* the instruction. A less-than sign is one character wide and sits between two values. If it stretches, it is music; if it fits between two numbers, it is mathematics.