Control flow

if/else, while, the counted for loop, and the loop-control statements. Run a cell to see its output beside the expected one.

if / else if / else

Viv [1]

x = 2.0
if x < 1.0 {
    show 1.0
} else if x < 3.0 {
    show 2.0
} else {
    show 3.0
}

The counted loop

for i to n runs i from 0 to n−1.

Viv [2]

total = 0.0
for i to 5 {
    total += i
}
show total

while and break

Viv [3]

p = 1.0
while 1.0 < 2.0 {
    p = p * 2.0
    if p > 100.0 { break }
}
show p

continue

Sum only the loop indices above 2.

Viv [4]

s = 0.0
for i to 6 {
    if i < 2.5 { continue }
    s += i
}
show s

Conditions compose with and / or / not

Viv [5]

x = 5.0
if x > 0.0 and not (x > 10.0) {
    show x
}

Nested loops

break leaves the innermost loop only.

Viv [6]

hits = 0.0
for i to 3 {
    for j to 5 {
        if j > 1.5 { break }
        hits += 1.0
    }
}
show hits

Computed and fractional bounds

The bound is any expression; i counts 0, 1, 2, … while i < bound, so a bound of 2.5 runs three times.

Viv [7]

n = 2.0 * 3.0
c1 = 0.0
for i to n { c1 += 1.0 }
show c1
c2 = 0.0
for k to 2.5 { c2 += 1.0 }
show c2

The loop variable outlives a top-level loop

At top level the loop variable is a global; after the loop it holds its last value.

Viv [8]

for i to 3 {
    x = i
}
show i

A while that never runs

Viv [9]

ran = 0.0
while 1.0 > 2.0 {
    ran = 1.0
}
show ran

Collatz length

A while loop with if/else inside; mod(n, 2) tells even from odd.

Viv [10]

def collatz_len(n) {
    steps = 0.0
    while n > 1.5 {
        if mod(n, 2.0) < 0.5 {
            n = n / 2.0
        } else {
            n = 3.0 * n + 1.0
        }
        steps += 1.0
    }
    return steps
}
show collatz_len(27.0)

An if expression

Only the branch chosen is computed.

Viv [11]

x = -2.0
show "neg" if x < 0.0 else "pos"
print(x, "and", x * x, sep=" ")

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