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Chapter 9

For - Next Statement in QBASIC

Class 7 - APC Understanding Computer Studies


State whether the following statements are True/False

Question 1

FOR statement may or may not be followed by NEXT.
False

Question 2

FOR-NEXT statement is used to generate finite loops.
True

Question 3

A loop can also be generated using the GOTO statement.
False

Question 4

The initial value of the variable FOR may begin with a negative number.
True

Question 5

By default, the increment of the variable in a FOR-NEXT statement is +1.
True

Question 6

Without using the STEP value, the control may jump to the next value.
True

Answer the following questions

Question 1

What is a loop?

Answer

A loop is a conditional repetitive type of flow and the program runs until the condition is satisfied. A task repeated again and again for a fixed number of times is known as a loop.

Question 2

What are the different ways to generate a loop in BASIC programming?

Answer

In BASIC programming, we can generate a loop by using:

  1. Counter method
  2. WHILE-WEND loop
  3. FOR-NEXT loop
  4. Do WHILE loop

Question 3

Explain the following with an example:
(a) Continuous loop
(b) Step loop

Answer

(a) Continuous loop: If the increment of the loop variable is by one, then it is known as a continuous loop.

Example:

CLS
FOR I = 1 TO 10
PRINT "CONTINUOUS LOOP"
NEXT I
END

(b) Step loop: If the increment of the loop variable is defined by STEP and the value is other than one, then it is known as a step loop.

Example:

CLS
FOR I = 1 TO 10 STEP 2
PRINT "CONTINUOUS LOOP"
NEXT I
END

Question 4

Write down the format of:
(a) WHILE - WEND
(b) FOR-NEXT

Answer

(a) WHILE - WEND The format of WHILE - WEND is as follows:

WHILE <condition>
...
task to be done
...
WEND

(b) FOR - NEXT The format of FOR - NEXT is as follows:

FOR <variable> = <initial value> TO <Final value>
...
Task to be done
...
NEXT <variable>

QBASIC Programming using FOR-NEXT

Question 1a

Draw a flowchart and write a program in QBASIC to display the first 10 terms of the series 3, 6, 12, 24, .......

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to display the first 10 terms of the series: 3, 6, 12, 24. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let A = 3
For I = 1 To 10
    Print A;
    A = A * 2
Next I
End

Output

3  6  12  24  48  96  192  384  768  1536

Question 1b

Draw a flowchart and write a program in QBASIC to display the first 10 terms of the series -1, 2, 5, 8, .......

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to display the first 10 terms of the series: -1, 2, 5, 8. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let A = -1
For I = 1 To 10
    Print A;
    A = A + 3
Next I
END

Output

-1  2  5  8  11  14  17  20  23  26

Question 1c

Draw a flowchart and write a program in QBASIC to display the first 10 terms of the series 7, 14, 21, .......

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to display the first 10 terms of the series: 7, 14, 21. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let A = 7
For I = 1 To 10
    Print A;
    A = A + 7
Next I
End

Output

7  14  21  28  35  42  49  56  63  70

Question 2a

Draw a flowchart and write a program in QBASIC to display the sum of the first 10 terms of the series S = 5 + 8 + 11 + .......

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to print the first 10 terms of the series: S = 5 + 8 + 11. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let A = 5
Let S = 0
For I = 1 To 10
    S = S + A
    A = A + 3
Next I
Print "Sum = "; S
End

Output

Sum = 185

Question 2b

Draw a flowchart and write a program in QBASIC to display the sum of the first 10 terms of the series S = 99 + 90 + 81 + .......

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to print the first 10 terms of the series: S = 99 + 90 + 81. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let A = 99
Let S = 0
For I = 1 To 10
    S = S + A
    A = A - 9
Next I
Print "Sum = "; S
End

Output

Sum = 585

Question 2c

Draw a flowchart and write a program in QBASIC to display the sum of the first 10 terms of the series S = 1 + 2 + 4 + 8 + .......

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to print the first 10 terms of the series: S = 1 + 2 + 4 + 8. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let A = 1
Let S = 0
For I = 1 To 10
    S = S + A
    A = A + A
Next I
Print "Sum = "; S
End

Output

Sum = 1023

Question 3

Draw a flowchart and write a program in QBASIC to enter the name and marks secured in 12 subjects in a term examination. Display the name, total and the average marks.

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to enter the name and marks secured in 12 subjects in a term examination. Display the name, total and the average marks. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
Let T = 0
Let AVG = 0
Input "Enter name"; N$
For I = 1 To 12
    Input "Enter marks"; M
    T = T + M
Next I
AVG = T / 12
Print "Name - "; N$
Print "Total marks -"; T
Print "Average marks - "; AVG
End

Output

Enter name? Richa
Enter marks? 89
Enter marks? 89
Enter marks? 87
Enter marks? 90
Enter marks? 99
Enter marks? 95
Enter marks? 97
Enter marks? 92
Enter marks? 78
Enter marks? 95
Enter marks? 78
Enter marks? 80
Name - Richa
Total marks - 1069
Average marks - 89.08334

Question 4

Draw a flowchart and write a program in QBASIC to calculate the area and the perimeter of 10 different rectangles. Take the length and breadth as inputs and display the result.

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to calculate the area and the perimeter of 10 different rectangles. Take the length and breadth as inputs and display the result. Class 7 ICSE Understanding Computer Studies

QBASIC Program

Cls
For I = 1 To 10
    Input "Enter length and breadth"; L, B
    A = L * B
    P = 2 * (L + B)
    Print "Area = "; A
    Print "Perimeter = "; P
Next I
End

Output

Enter length and breadth? 2,1
Area = 2
Perimeter = 6
Enter length and breadth? 2,3
Area = 6
Perimeter = 10
Enter length and breadth? 2,4
Area = 8
Perimeter = 12
Enter length and breadth? 3,4
Area = 12
Perimeter = 14
Enter length and breadth? 3,5
Area = 15
Perimeter = 16
Enter length and breadth? 3,6
Area = 18
Perimeter = 18
Enter length and breadth? 4,5
Area = 20
Perimeter = 18
Enter length and breadth? 5,8
Area = 40
Perimeter = 26
Enter length and breadth? 6,9
Area = 54
Perimeter = 30
Enter length and breadth? 7,8
Area = 56
Perimeter = 30

Question 5

A class teacher wants to calculate the average marks obtained by a student in three terms in a class of 50 students. Draw a flowchart and write a program in QBASIC to enter the name and the total marks obtained by a student in three terms. Display the result along with the name.

Answer

Flowchart

A class teacher wants to calculate the average marks obtained by a student in three terms in a class of 50 students. Draw a flowchart and write a program in QBASIC to enter the name and the total marks obtained by a student in three terms. Display the result along with the name. Class 7 ICSE Understanding Computer Studies.

QBASIC Program

Cls
For I = 1 To 50
    Input "Enter name"; N$
    Input "Marks of three terms"; T1, T2, T3
    AVG = (T1 + T2 + T3) / 3
    Print "Name - "; N$
    Print "Average marks - "; AVG
Next I
End

Question 6

Draw a flowchart and write a program in QBASIC to display 10 different values of the expression (a + b)2. Take the values of a and b as inputs after each iteration.

Answer

Flowchart

Draw a flowchart and write a program in QBASIC to display 10 different values of the expression (a + b)^2. Take the values of a and b as inputs after each iteration. Class 7 ICSE Understanding Computer Studies.

QBASIC Program

Cls
For I = 1 To 10
    Input "Enter two values"; A, B
    S = (A + B) ^ 2
    Print "(A+B)^2 = "; S
Next I
End

Output

Enter two values? 2,3
(A+B)^2 = 25
Enter two values? 4,2
(A+B)^2 = 36
Enter two values? 6,3
(A+B)^2 = 81
Enter two values? 5,8
(A+B)^2 = 169
Enter two values? 3,3
(A+B)^2 = 36
Enter two values? 4,4
(A+B)^2 = 64
Enter two values? 5,5
(A+B)^2 = 100
Enter two values? 6,1
(A+B)^2 = 49
Enter two values? 4,8
(A+B)^2 = 144
Enter two values? 3,9
(A+B)^2 = 144

Correct the errors in the following flowcharts and write the programs

Question 1

Correct the mistakes in the given flowchart. Chapter 9 Question 1 Class 7 ICSE Understanding Computer Studies.

Answer

Flowchart

Corrected flowchart for Chapter 9 Question 1 Class 7 ICSE Understanding Computer Studies.

QBASIC Program

Cls
Input "Enter a number"; N
For I = 1 To N
    M = I + I
    Print M
Next I
End

Output

Enter a number? 5
2
4
6
8
10

Question 2

Correct the mistakes in the given flowchart. Chapter 9 Question 2 Class 7 ICSE Understanding Computer Studies.

Answer

Flowchart

Corrected flowchart for Chapter 9 Question 2 Class 7 ICSE Understanding Computer Studies.

QBASIC Program

Cls
Input "Enter a value"; N
For I = 1 To N
    Input "ENTER YOUR HEIGHT IN METRES"; M
    CM = M * 100
    Print CM
Next I
End

Output

Enter a value? 2
Enter your height in metres? 4
400
Enter your height in metres? 5
500
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