4.4 Cau truc if-else-end.
Nhieu khi ta can cac cau lenh doc thuc hien theo mot dieu kien nao do. Trong ngon ngu lap trinh matlab, logic nay doc cung cap boi cau truc if-else-end. Cu phap cua cau truc nay nh sau:
if bieu thuc dieu kien
khoi cac lenh doc thuc hien neu dieu kien la dung
else
khoi cac lenh doc thuc hien neu dieu kien la sai.
end.
Vi du:
>> i=1;
>> j=2;
>> if i>j
a=6
else
a=-6
end
a =
-6
Khi co ba hoac nhieu dieu kien thay doi, cau truc cua no se la
if bieu thuc dieu kien 1
khoi cac lenh doc thuc hien neu dieu kien 1 la dung.
elseif bieu thuc dieu kien 2
khoi cac lenh doc thuc hien neu dieu kien 2 la dung.
elseif bieu thuc dieu kien 3
khoi cac lenh doc thuc hien neu dieu kien 3 la dung.
elseif bieu thuc dieu kien 4
else
khoi cac lenh doc thuc hien neu khong co dieu kien nao la dung.
end
>> i=2
i =
2
>> if i==3
a=4
elseif i==4
a=5
elseif i==5
a=6
else
a=7
end
a =
7
Trong mau dang nay thi bieu thuc dieu kien dau tien dung thi cac cau lenh sau khong doc kiem tra nua, cac cau truc if-else-end con lai doc bo qua. Hon nua cau lenh else o cuoi co the khong can cho vao.
Cau truc if-else-end cung co the long nhau.
4.5 Cau truc switch-case
Khi mot chuoi cac lenh doc thuc hien dua tren mot bieu thuc thu (hoac bieu thuc dieu kien) voi nhieu gia tri thu khac nhau, ngoi ta thong dung cau truc switch-case. Cau truc switch-case co danh nh sau:
switch bieu thuc dieu kien.
case gia tri thu 1
khoi lenh 1
case { gia tri thu 2, gia tri thu 3, gia tri thu 4}
khoi lenh 2
otherwise
khoi lenh 3
end
Tai day bieu thuc dieu kien phai la dang so hoac dang chuoi, neu bieu thuc dieu kien la dang so thi lenh case se thu xem gia tri cua bieu thuc co bang gia tri thu i khong. Neu bieu thuc dieu kien la mot chuoi thi lenh case se so sanh chuoi do voi gia tri thu i. Trong trong hop tren, bieu thuc dieu kien doc dem so sanh voi gia tri thu 1, neu chung bang nhau thi khoi lenh dau tien doc thuc hien, ma cac khoi lenh tiep theo cho den troc trang thai end doc bo qua. Neu chung khong bang nhau thi dieu kien tiep tuc doc so sanh voi gia tri thu 2, gia tri thu 3, gia tri thu 4 , neu mot trong cac gia tri nay bang bieu thuc dieu kien thi khoi lenh 2 doc thuc hien.
Chu y rang la trong switch-case phai co it nhat mot nhom lenh phai doc thuc hien.
Vi du:
>> i=3
i =
3
>> switch i
case 2
a=1
case 3
a=2
case 4
a=3
otherwise
a=4
end
a =
2
