字符串函数的请教

zsq

new
def afill ;fill matrix with random numbers
array var(4,3)
loop m (1,4)
loop n (1,3)
var(m,n) = urand
endloop
endloop
end
def ashow ;display contents of matrix
loop m (1,4)
hed = ’ ’
msg = ’ ’+string(m)
loop n (1,3)
hed = hed + ’ ’+string(n)
msg = msg + ’ ’+string(var(m,n))
endloop
if m = 1
dum = out(hed)
endif
dum = out(msg)
endloop
end
afill
Ashow
请问大家，‘’这个里面无字符串是什么意思？
hed = hed + ’ ’+string(n)，这个是什么意思，谢谢