1. Control Structure
There are two kind of control structure in GWBASIC one is iteration/loop or repetitive and second make decision/condition.
Iteration/Loop
The Loop mean one or more statements execute many times is called Loop. Here control transfer always upward. There are two types of loops.
For … Next
While .. Wend

2. Control Structure For .. Next
The for next loop allows programs to repeat a statement or statements, as long as a certain is number of times.
Syntax
For Variable = Start No. To Stop No. [ Step Increment No.]
statement1
statement2 ..
Next

3. Control Structure While .. Wend
The while loop allows programs to repeat a statement or series of statement, over and over, as long as a certain test condition is true.
Syntax
While test
statement1
statement2 ..
Wend

4. Practical #15
Write a program to calculate current value at five different resistance values are from 1 to 5 here constant voltage is 5 by using loops. Formula is I=V/R.

5. 15 print “Current = Voltage / resistance “ 20 for r = 1 to 5
10 Key Off
15 print “Current = Voltage / resistance “
20 for r = 1 to 5
30 let v=5
Let I = v / r
print I ; “=“ ; v ; “/” ; r
60 next
70 end
Out Put
10 CLS
20 Print “Current = Voltage / resistance “
30 r=1
40 While r <= 5
50 let v=5
60 Let I = v / r
70 Print I ; “=“ ; v ; “/” ; r
80 r=r+1
90 Wend
100 End

6. Out Put Current Voltage Resistance ===================================