"Testing for"

clear

k = 123
A = zero(3)
f(x) = for(k,1,3,A[k] = x)
f(1)
check(A == (1,1,1))
check(k == 123)

clear

x = 0
y = 2
for(k,1,9, x = sqrt(x + 2), y = 2 y / x)
check(infixform(float(y)) == "3.14159")

for(i,1,3,j=i)
check(i = sqrt(-1))
check(j = 3)

t = 0
A = 2 k
for(k,1,3, t = t + A)
check(t == 12)
