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Julia provides a variety of control flow constructs:
Compound Expressions: begin and ;.
Conditional Evaluation: if-elseif-else and ?: (ternary operator).
Short-Circuit Evaluation: logical operators && (“and”) and || (“or”), and also chained comparisons.
Repeated Evaluation: Loops: while and for.
复合表达式 Compound Expressions
可以使用begin...end 或者;，z为最后一个表达式的结果
z = begin
x = 1
y = 2
x + y
end
z = (x = 1; y = 2; x + y)
begin x = 1; y = 2; x + y end
条件语句Conditional Evaluation
if 后边只能是布尔值即(true 或 false)，和Python不同可以放None表示False
if x < y
println("x is less than y")
elseif x > y
println("x is greater than y")
else
println("x is equal to y")
end
三元运算符ternary operator
注意R的ifelse是向量化的，也就是说test可以是多个布尔值
# python
a if test else b #如果test为真则返回a,否则返回b #
# R
ifelse(test,a,b) # 向量化
# Julia
test ? a:b
短路运算Short-Circuit Evaluation
可以替换if判断
function fact(n::Int)
if n<0:
println("n must be non-negative")
end
if n==0:
return 1
end
n * fact(n-1)
end
function fact(n::Int)
n >= 0 || println("n must be non-negative")
n == 0 && return 1
n * fact(n-1)
end
循环Repeated Evaluation: Loops
while循环
i = 1;
while i <= 5
println(i)
global i += 1
end
for循环
for i = 1:5
println(i)
end
break
结果为1:5。如果j≥5就直接跳出循环
for j = 1:1000
println(j)
if j >= 5
break
end
end
continue
结果为3,6,9。如果i不是3的整倍数，那么就不运行println(i)，直接进入下一次循环
for i = 1:10
if i % 3 != 0
continue
end
println(i)
end
嵌套for循环nested for
第一种相当于i和j的笛卡尔积，第二种是对应位置组合，如果位数不相同，那么只保留短的。
for i = 1:3, j = 4:7
println((i, j))
end
# (1, 4)
# (1, 5)
# (1, 6)
# (1, 7)
# (2, 4)
# (2, 5)
# (2, 6)
# (2, 7)
# (3, 4)
# (3, 5)
# (3, 6)
# (3, 7)
for (j, k) in zip([1 2 3], [4 5 6 7])
println((j,k))
end
# (1, 4)
# (2, 5)
# (3, 6)
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