if/else Statements
if (i > 4) {
// Do sth
} else if (i > 2) {
// Do sth else
} else { // Do sth else }- must be a Boolean value or evaluate to Boolean value
- 0 = false, non-zero = true
Initializers for if Statements
Format
if (<initializer>; <conditional_expression>) {
<if_body>
} else if (<else_if_expression>){
<else_if_body>
} else { <else_body>}Example
if (Employee employee { getEmployee() }; employee.salary > 1000) { ... }
The Conditional Operator
- aka ternary operator.
- “If [something], then [perform action], otherwise [perform some other action].”
cout << ((i > 2) ? "yes" : "no");
Logical Operators
| Operator | Description | Usage |
|---|---|---|
<, <=, >, >= | Relational comparisons (same as math) | if (i < 0) { … } |
== | Equality | if (i == 3) { … } |
!= | Inequality | if (i != 3) { … } |
<=> | Three-way comparison (spaceship) | auto r = i <=> 0; |
! | Logical NOT | if (!flag) { … } |
&& | Logical AND | if (a && b) { … } |
\|\| | Logical OR | if (a \|\| b) { … } |
- C++ uses short-circuit logic when evaluating logical expressions (if final result is certain, rest of expression is not considered)
bool result { bool1 || bool2 || (i > 7) || (27 / 13 % i + 1) < 2 };- If
bool1is true, rest is not checked < - Better for performance but potential source of bugs
- If
- Can be useful in context of pointers to avoid parts of expressions to be executed wehn pointer is not valid
Three-Way Comparisons (C++20)
<=>(spaceship operator): can tell whether value is equal, less than or greater than another value- Cannot be boolean since it returns more than true or false - returns enumeration-like type defined in
<compare>and in thestdnamespace - returns either
std::strong_ordering(for integrals operand),std::weak_ordering(for custom-defined types), orstd::partial_ordering(for floating-point types) (example 1)- In
<compare>header, there's predicates s.t. we don't have to writestrong_ordering::lessevery time (example 2)
Example 1
- In
int i { 11 };
strong_ordering result { i <=> 0 };
if (result == strong_ordering::less) {
cout << "less" << endl; }
if (result == strong_ordering::greater) {
cout << "greater" << endl; }
if (result == strong_ordering::equal) {
cout << "equal" << endl; }Example 2
#include <compare>
using namespace std;
int main() {
int i{11};
// 1) Use the spaceship operator; it yields a strong_ordering
strong_ordering result = (i <=> 0);
// 2) Interpret that ordering with the helper functions:
if (is_lt(result)) cout << "i is less than 0\n";
if (is_eq(result)) cout << "i is equal to 0\n";
if (is_gt(result)) cout << "i is greater than 0\n";
return 0;
}switch Statements
- must be of an integral type (int, char, etc.) , a type convertible to an integral type (bool), enumerated type, or strongly typed enumeration (enum class), and must be compared to constants
- Can also use initializers:
switch (<initializer>; <expression>) { <body> }
Fallthrough
- Fallthrough: continuation of execution of
caseexpression even though it's been caught at some point- Example 1 will go through
StandardandDefaulteven though if it gets caught inStandard - Can be source of bugs if
breaknot implemented correctly. Compiler will usually issue warning, but if this is intentional, use[[fallthrough]]to tell compiler this is intentional (example 2)
- Example 1 will go through
Example 1
enum class Mode { Default, Custom, Standard };
int main() {
int value { 42 };
Mode mode { /* ... */ };
switch (mode) {
using enum Mode; // Allows direct use of enum values without qualification
case Custom:
value = 84;
break; // Added break to prevent fallthrough
case Standard:
case Default:
// Do something with value
std::cout << "Value: " << value << std::endl;
break;
}
return 0;
}Example 2
switch (mode) {
using enum Mode; // Allows direct use of enum values without qualification
case Custom:
value = 84;
[[fallthrough]];
case Standard:
case Default:
// Do something with value
std::cout << "Value: " << value << std::endl;
break;
}
Hi!