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To add to the excellent explanation by FractionalRadix, it's worth mentioning that sometimes the line between expressions and statements can seem a little blurry (at least to the observer — the lan...
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#2: Post edited
- To add to the excellent explanation by FractionalRadix, it's worth mentioning that sometimes the line between expressions and statements can seem a little blurry (at least to the observer — the language specification will almost certainly define the boundaries clearly and precisely).
- For example, in C we have the expression `++i`, which means "add one to the value of `i` and return the new value". This is an expression because it yields a value, but it also makes a change to the program state. Therefore you can use it as a "pure" expression and assign it to something else:
- int iNew = ++i; // increment i, put incremented value into iNew
- or you can use it as a statement in its own right:
- ++i; // increment i and do nothing else
- Also in C, a simple assignment can be an expression as well as a statement, e.g.
- int x = 2; // statement
- int y = (x = 3); // y and x are now both equal to 3
- Informally, you can think of an expression as something you **can** (but don't necessarily **have to**) put on the right-hand side of an assignment operation.
Languages may also different in which constructs they treat as statements or expressions. In Rust, an `if` construct is actually an expression, not a statement, and can be assigned as a value:- let x = if (y == 2) { 5 } else { 10 };
- If you try this in C you'll get a compilation error because `if` is a statement and does not evaluate to a value:
int x = if (y == 2) { 5; } else { 10; } // INVALID; won't compile
- To add to the excellent explanation by FractionalRadix, it's worth mentioning that sometimes the line between expressions and statements can seem a little blurry (at least to the observer — the language specification will almost certainly define the boundaries clearly and precisely).
- For example, in C we have the expression `++i`, which means "add one to the value of `i` and return the new value". This is an expression because it yields a value, but it also makes a change to the program state. Therefore you can use it as a "pure" expression and assign it to something else:
- int iNew = ++i; // increment i, put incremented value into iNew
- or you can use it as a statement in its own right:
- ++i; // increment i and do nothing else
- Also in C, a simple assignment can be an expression as well as a statement, e.g.
- int x = 2; // statement
- int y = (x = 3); // y and x are now both equal to 3
- Informally, you can think of an expression as something you **can** (but don't necessarily **have to**) put on the right-hand side of an assignment operation.
- Languages may also differ in which constructs they treat as statements or expressions. In Rust, an `if` construct is actually an expression, not a statement, and can be assigned as a value:
- let x = if (y == 2) { 5 } else { 10 };
- If you try this in C you'll get a compilation error because `if` is a statement and does not evaluate to a value:
- int x = if (y == 2) { 5; } else { 10; } // INVALID; won't compile
- But in Python, you can't treat an assignment as an expression like you can in C, unless you use a special [recently-introduced syntax](https://peps.python.org/pep-0572/):
- x = 2
- y = (x = 3)
- ^
- SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?
- y = (x := 3) # x and y are now both 3
#1: Initial revision
To add to the excellent explanation by FractionalRadix, it's worth mentioning that sometimes the line between expressions and statements can seem a little blurry (at least to the observer — the language specification will almost certainly define the boundaries clearly and precisely).
For example, in C we have the expression `++i`, which means "add one to the value of `i` and return the new value". This is an expression because it yields a value, but it also makes a change to the program state. Therefore you can use it as a "pure" expression and assign it to something else:
int iNew = ++i; // increment i, put incremented value into iNew
or you can use it as a statement in its own right:
++i; // increment i and do nothing else
Also in C, a simple assignment can be an expression as well as a statement, e.g.
int x = 2; // statement
int y = (x = 3); // y and x are now both equal to 3
Informally, you can think of an expression as something you **can** (but don't necessarily **have to**) put on the right-hand side of an assignment operation.
Languages may also different in which constructs they treat as statements or expressions. In Rust, an `if` construct is actually an expression, not a statement, and can be assigned as a value:
let x = if (y == 2) { 5 } else { 10 };
If you try this in C you'll get a compilation error because `if` is a statement and does not evaluate to a value:
int x = if (y == 2) { 5; } else { 10; } // INVALID; won't compile