Computer Programming. Loops(2) do-while, for

Transcription

1 Computer Programming Loops(2) do-while, for

2 Topics Repeating Statements (review) while loop (review) do-while loop for loop Infinite loops Examples

3 Repeating Statements In many cases same operations are repeated for different data. For example, finding average of a student is repeated for other students too. In these cases, we can use a statement called a loop The statements inside a loop are repeated until its condition becomes false. C uses three types of loops: While loop (discussed last week) Do-while loop For loop

4 While Loop While loop repeats a group of C statements until its condition becomes false While loop has the following syntax: while(condition) [statements]; Condition is a logical expression Statements inside the while loop are called body of while loop If more than one statement is written inside body of a while loop, they should be put in }

5 Example 1 Write a program to print all positive even integers less than 100. The output should be like:

6 #include<stdio.h> void main() int count; count = 2; while( count < 100 ) printf( %d\n, count); count = count + 2; } }

7 Example 2 Write a program to read a series of positive integers and find their sum until -1 is entered. Example input can be: Output: 23 Example input can also be: -1 Output: 0 In all cases the input has at least one number (at lease -1 is entered)

8 #include<stdio.h> void main() int num, sum; sum = 0; printf( Enter an integer:\n ); scanf( %d,&num); while( num!= -1) sum = sum + num; printf( Enter an integer:\n ); scanf( %d,&num); } printf( The sum of the numbers is %d \n, sum); }

9 Do While Loop do-while loop is the same as while loop except that the condition is checked at the end of the loop. do-while syntax is: do [Loop Body] }while( condition); The body is execute until the condition becomes false As the condition is checked at the end, the loop is executed at least once.

10 Example 3 Re-write previous example with do-while loop [Notice that scanf is written only once]

11 #include<stdio.h> void main() int num, sum; sum = 0; do printf( Enter an integer:\n ); scanf( %d,&num); if( sum!= -1 ) sum = sum + num; } while( num!= -1); } printf( The sum of the numbers is %d \n, sum);

12 For Loop (1) Whenever you know the number of repetitions in a loop, for loop is used. In a loop which counts the repetitions, you need a counter ( a variable defined in your program) The counter is initialized before the loop. The counter is updated inside the body of the loop For loop does: Gives initial value to counter Updates the counter Checks loop condition

13 For Loop (2) For loop syntax: for ( initial value assignment ; condition ; update counter ) [loop body statements] }

14 Example 4 Write a program to find sum of the integer numbers from 1 to 10. #include<stdio.h> void main() int count, sum; sum = 0; for( count = 1; count <=10 ; count ++ ) sum = sum+count; printf( The sum of positive integer up to 10 is %d\n,sum); }

15 Example 5 Write a program to read a positive integer and find its factorial. #include<stdio.h> void main() int count, num, fact; fact = 1; scanf( %d,&num); if( num > 0 ) for( count = 1; count <=10 ; count ++ ) fact = fact*count; printf( The factorial of %d is %d\n,num,fact); } else printf( You entered a non-positive number\n ); }

16 For Loop Without Initialization You may have no initialization in a for loop. In this case you can leave the first part empty however, you need to put the ; Therefore the syntax of for loop without initialization will be for( ; condition ; update counter ) [loop body]

17 Example 6 Write a C program to compute the discount offered to a customer by an insurance company. The company has the following rules: A customer gets a discount for each year of being registered with the company. For each year, the age of the customer is multiplied by 0.05 The discount is the sum of the discounts given for each year For example, if the customer registers when he is 30, and his current age is 34, he gets a discount as below: Discount = (30* * * *0.05) % Discount = 6.3 %

18 #include<stdio.h> void main() int startage, currentage; float discount ; discount = 0; printf( Enter the age you started insurance, and your current age: \n ); scanf( %d%d, &startage, &currentage); for( ; startage < currentage ; startage ++) discount = discount + startage*0.05; printf( The total discount is %f\n, discount ); } Note: The initialization part of the loop is empty here

19 For Loop without Condition Part The condition part is optional in for loops A loop without a condition should still include ; characters to separate three parts of the loop for( initialization ; ; update ) [body statements] A loop without a condition will not terminate. These loops are called infinite loops You can terminate a for loop without a condition using break statement.

20 Example 7 Assume 3 people labeled as A, B, and C are playing a game. The user enters an integer number. If the number is divisible by 7 A gets 1 point. If the number is divisible by 11 B gets 2 point, If the number is divisible by 13 C will get 3 point. The program ends when -1 is entered. The score of each player is the total point he gets divided by the number of times user enters a number Example: with data 3, 6, 7, 11, 33, 21, 39 scores are: A=2/7 B=4/7 C=3/7 Write a C program to compute the scores in this game

21 #include<stdio.h> void main() float scorea, scoreb, scorec; int nextnum, count ; scorea = scoreb = scorec = 0; No condition part in for for( count = 0 ; ; count ++ ) loop printf( Enter next number: \n ); scanf( %d, &nextnum); if( nextnum == -1 ) break ; if( nextnum % 7 == 0 ) scorea = scorea + 1; if( nextnum % 11 == 0 ) scoreb = scoreb + 2; if( nextnum % 13 == 0 ) scorec = scorec + 3; } scorea = scorea / count; scoreb = scoreb / count; scorec = scorec / count; printf( The scores are: A=%f B=%f C=%f\n, scorea, scoreb, scorec ); }

22 For Loop without update counter Part The update counter part of a for loop is also optional If you decide not to have update counter part in a for loop you should: Update the variable inside the body of the loop, otherwise the condition will not change and the loop will not terminate. Include ; even if update part is omitted. A for loop without initialization and update parts is the same as a while loop

23 Example 8 Assume we want to compare the probability of getting a total of 10 when we roll two dice with the probability of getting a total of 9. For instance, the number of times you get (4,6) or (5,5) compared to the probability of getting (3,6) or (4,5), etc. Write a C program to read two positive integer and find out their sum. The program should count the number of times that you get 10, and the number of times you get 9. The program terminates when you get twenty 10s or 9s. Hint: Make sure that the numbers are between 1 and 6

24 #include<stdio.h> void main() int dice1, dice2, tens, nines; nines = tens = 0; for( ; tens < 20 && nines < 20 ; ) printf( Enter dice numbers \n ); scanf( %d%d, &dice1, &dice2); if( dice1 < 1 dice1 > 6 dice1 < 1 dice2 > 6) printf( You entered invalid numbers\n ); else if( dice1 + dice 2 == 10 ) tens++; if( dice1 + dice 2 == 9 ) nines ++; } } /* end of for loop */ if( nines == 20 ) printf( The total of 9 is more probable\n ); else printf( The total of 10 is more probable\n ); }

25 Summary If parts of a program are repeated with different values, we can use a loop Do-While loop repeats executing the statements until the condition becomes false. Do-while is executed at least once For loops have initialization, condition, and update parts All parts of a for loop are optional

26 Questions?