极客教程Tcl 运算符优先级
运算符优先级决定了表达式中项的分组情况。这影响了表达式的计算顺序。某些运算符的优先级比其他运算符高；例如，乘法运算符的优先级高于加法运算符。
例如： x = 7 + 3 * 2; 这里，x被赋值为13，而不是20，因为运算符*的优先级高于+，所以它首先与3 * 2相乘，然后再加到7上。
在表中，具有最高优先级的运算符出现在顶部，优先级最低的运算符出现在底部。在一个表达式中，高优先级的运算符将首先被计算。
| Category | Operator | Associativity |
|---|---|---|
| Unary | + - |
Right to left |
| Multiplicative | * / % |
Left to right |
| Additive | + - |
Left to right |
| Shift | << >> |
Left to right |
| Relational | < <= > >= |
Left to right |
| Equality | == != |
Left to right |
| Bitwise AND | & |
Left to right |
| Bitwise XOR | ^ |
Left to right |
| Bitwise OR | | |
Left to right |
| Logical AND | && |
Left to right |
| Logical OR | || |
Left to right |
| Ternary | ?: |
Right to left |
示例
请尝试以下示例以了解Tcl语言中提供的操作符优先级 –
#!/usr/bin/tclsh
set a 20
set b 10
set c 15
set d 5
set e [expr [expr a +b] * c /d ] ;# ( 30 * 15 ) / 5
puts "Value of (a + b) * c / d is : e\n"
set e [expr [expr [expra + b] *c] / d] ;# (30 * 15 ) / 5]
puts "Value of ((a + b) * c) / d is :e\n"
set e [expr [expr a +b] * [expr c /d] ] ;# (30) * (15/5)
puts "Value of (a + b) * (c / d) is : e\n"
set e [expra + [expr b *c ] / d ] ;# 20 + (150/5)
puts "Value of a + (b * c) / d is :e\n"
当你编译并执行以上程序时，它会产生以下结果 –
Value of (a + b) * c / d is : 90
Value of ((a + b) * c) / d is : 90
Value of (a + b) * (c / d) is : 90
Value of a + (b * c) / d is : 50