请看看这个程序有什么错

macro_command main()
char  a,b=12,c=13
bool off=0
GetData(a, "Local HMI", LW, 10, 1)
if a==’yh’ then
SetData(b, "Local HMI", LW, 0, 1)
else if a==’YH ‘then
SetData(c, "Local HMI", LW, 0, 1)
end if
SetData(off, "Local HMI", LB, 0, 1)
end macro_command

if a==’y' and 'h’ then
SetData(b, "Local HMI", LW, 0, 1)
else if a==’Y' and 'H ‘ then
SetData(c, "Local HMI", LW, 0, 1)
end if
SetData(off, "Local HMI", LB, 0, 1)
试过可用。
但不明白，a=='yh' 或a=="yh"都不行。求解答！