4.2 Vong lap for

Vong lap for cho phep mot nhom cau lenh thuc hien lap lai mot so lan co dinh. Cu phap cua vong lenh for nh­ sau.

for n=array

Command %Khoi cac lenh

end

So lan thuc hien cac cau lenh giua hai trang thai for va end bang so cot cua mang(array), tai moi lan thuc hien n se lan l­ot nhan gia tri cua tung cot trong mang.

Vi du:

>> for n=1:10

x(n)=5*n;

end

>> x

x =

5 10 15 20 25 30 35 40 45 50

Dau tien trong vong lap for n=1, tiep theo n=2, va cu nh­ vay cho den tr­ong hop n=10. Sau tr­ong hop n=10, vong lap for ket thuc va tat ca cac lenh sau trang end cua vong lap d­oc thuc hien.

Vong lap for khong the ket thuc bang cach gan lai bien dieu khien n trong vong lap

vi du tren n la mot vector hang bay gioi ta se xet den viec n la mot mang hai chieu.

>>data =[1 2 3 ; 4 5 6]

data =

1 2 3

4 5 6

>>for n=data

x=n*2

end

x =

2

8

x =

4

10

x =

6

12

Hai vong lap for co the long vao nhau:

>> for i=1:5

for j=1:6

a(i,j)=i+j;

end

end

>> a

a =

2 3 4 5 6 7

3 4 5 6 7 8

4 5 6 7 8 9

5 6 7 8 9 10

6 7 8 9 10 11

Khong nen dung lap for khi ma t­ong d­ong voi viec ta dung mang de tinh toan, vi viec dung mang nhanh hon va thao tac cung it hon.

4.3 Vong lap while

Vong lap while thuc hien lap lai mot nhom lenh mot so lan co dinh, nh­ng khong biet tr­oc d­oc so lan lap lai. Cu phap cua lenh while nh­ sau.

while bieu thuc dieu kien

Khoi cac lenh

end

" khoi cac lenh" giua hai trang thai while va end d­oc thuc hien lap di lap lai khi tat ca cac "bieu thuc dieu kien la dung". Thong th­ong gia tri cua dieu kien d­a ra ket qua la mot so, nh­ng neu ket qua la mang thi van hop le. Trong tr­ong hop mang, tat ca cac phan tu trong mang ket qua d­a ra phai la True (dung).

Chu y:

Boi vi vong lap while chi ket thuc khi bieu thuc dieu kien sai nen trong qua trinh thuc hien vong lap while phai co mot cau lenh lam cho bieu thuc dieu kien dan tro thanh sai.

Vi du:

>> i=1;

>> while i

a(i)=2*i;

i=i+1;

end

>> a

a =

2 4 6 8 10 12 14 16