Loops: Programming Approach in Problem Solving.pptx

Loops: Programming Approach in Problem Solving.pptx

1. Loops

2. Loops In programming often requires repeated execution of a sequence of operations. A loop is a basic programming construct that allows repeated execution of a fragment of source code. Depending on the type of the loop, the code in it is repeated a fixed number of times or repeats until a given condition is true (exists). Loops that never end are called infinite loops. Using an infinite loop is rarely needed except in cases where somewhere in the body of the loop a break operator is used to terminate its execution prematurely.

3. Loop Constructs A looping process, in general, would include the following steps : 1 . Setting and initialization of a counter. 2. Test for a specified condition for execution of the loop. 3. Incrementing the counter . The test may be either to determine whether the loop has been repeated the specified number of times or to determine whether a particular condition has been met with.

4. Why use Loops Eg : You need to add from 0 to 10 Solution not using loop: int answer; answer = 0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10; The above solution not suitable for very large numbers (says from 0 to 10000) , what would be a faster way to solve?

5. The C language provides 3 constructs for performing loop operations. They are: The for loop The while loop The do loop

6. for loop For -loops are a slightly more complicated than while and do-while loops but on the other hand they can solve more complicated tasks with less code. Here is the scheme describing for -loops:

7. Syntax of For loop

8. Since none of the listed elements of the for -loops is mandatory, we can skip them all and we will get an infinite loop :

9. For-Loop – Example Here is a complete example of a for -loop : Int i; for (i = 0; i <= 5; i++) { printf (“%d“, i ); } The result of its execution is : 0 1 2 3 4 5 Int i; for (i = 0; i <= 10; i++) { printf (“\n %d “, i ); } The result of its execution is : 1 2 3 . . . 10

10. int i; for (i = 0; i <= 10; i = i + 2) { printf( “\n %d“ ,i) } 2 4 6 8 10

11. Here is another, more complicated example of a for -loop, in which we have two variables Example 1: Example 2: int i , j; for ( i = 0, j = 10 ; i <= 10 && j >= 0 ; i ++, j-- ) { printf (" i = %d, j = %d\n", i , j); } int i, sum; for ( i = 1, sum = 1; i <= 25; i=i*2,sum+=i ) { printf("i = %d, sum = %d\n", i, sum); }

12. What to do if we want to print no's from 10 to 1

13. Calculating N^M – Example int m,n ; printf ("n = "); scanf ("% d",&n ); printf ("m = "); scanf ("%d", &m); long int result = 1; int i ; for ( i = 0; i < m; i ++) { result *= n; } printf (" n^m = % ld " , result); Here is how the outcome of the program for n = 2 and m = 10 looks like:

14. Calculating Factorial of any given no   int i , number; int fact = 1; printf ("Enter any Number: "); scanf ("%d", &number); for ( i = 1; i <= number; i ++) { fact = fact * i ; } printf ("Factorial of %d is: %d\n", number, fact); Enter any number: 4 Factorial of 4 is 24

15. While Loops One of the simplest and most commonly used loops is while. Syntax of For Loop In the above code example , condition is any expression that returns a Boolean result – true or false . It determines how long the loop body will be repeated and is called the loop condition .

16. In the while loop, first of all the Boolean expression is calculated and if it is true the sequence of operations in the body of the loop is executed. Then again the input condition is checked and if it is true again the body of the loop is executed. All this is repeated again and again until at some point the conditional expression returns value false. At this point the loop stops and the program continues to the next line, immediately after the body of the loop. The body of the while loop may not be executed even once if in the beginning the condition of the cycle returns false. If the condition of the cycle is never broken the loop will be executed indefinitely.

17. Difference between For and While For While Initialization may be either in loop statement or outside the loop. Initialization is always outside the loop. Once the statement(s) is executed then after increment is done. Increment can be done before or after the execution of the statement(s). It is normally used when the number of iterations is known. It is normally used when the number of iterations is unknown. Condition is a relational expression. Condition may be expression or non-zero value. It is used when initialization and increment is simple. It is used for complex initialization. Use While loop is used in situations where we do not know how many times loop needs to be executed beforehand. For loop is used where we already know about the number of times loop needs to be executed. Typically for a index used in iteration.

18. Summing the Numbers from 1 to N int n; printf("n = "); scanf("%d", &n); int num = 1; int sum = 1; printf("\n nums are: %d" , num); while (num < n) { num++; sum += num; printf("\n nums are: %d" , num); } printf("\n %d", sum);

19. Calculating Factorial – Example int n; int fact=1; printf ("input n = "); scanf ("%d", &n); while (n > 0) { fact *= n; n--; } printf ("n! = %d" ,fact);

20. Check If a Number Is Prime int n, i = 2, isPrime = 1; // assume prime ( isPrime = 1 ) printf ("Enter a number: "); scanf ("%d", &n ); if (n <= 1) { isPrime = 0; // 0 and 1 are not prime } else { while ( i <= n / 2) { if (n % i == 0) { // divisible by i isPrime = 0; // not prime break ; } i ++; } } if ( isPrime ) printf ("%d is a prime number.\n", n); else printf ("%d is not a prime number.\n", n);

21. Do-While Loops The do-while loop is similar to the while loop, but it checks the condition after each execution of its loop body. This type of loops is called loops with condition at the end (post-test loop). A do-while loop looks like this: do { executable code; } while (condition);

22. Difference between While and Do While T he main difference between a while loop and do while loop is that while loop check condition before iteration of the loop. On the other hand, the do-while loop verifies the condition after the execution of the statements inside the loop . So do while will execute at least 1 even if condition is false int a=1; while(a>10) { printf ("% d",a ); a++; } Output Nothing will print because condition a>10 is not true int a=1; do { printf ("% d",a ); a++; } while(a>10); } Output This will print 1 first add 1and then check the condition which is false then loop will break.

23. Calculating Factorial – Example int n; int fact = 1; printf("input n = "); scanf("%d", &n); do { fact *= n; n--; } while (n > 0); printf("n! = %d\n", fact);

24. Product in the Range [N…M] – Example int N, M; long long product = 1; // use long long to handle large results printf ("Enter starting number (N): "); scanf ("%d", &N ); printf ("Enter ending number (M): "); scanf ("%d", &M ); if (N > M) { printf ("Invalid range! N should be <= M.\n"); return 0; } int i = N; // start from N do { product *= i ; i ++; } while ( i <= M); printf ("Product of numbers from %d to %d is: % lld \n", N, M, product);

25. Break and Continue in Loops Break and continue is a very basic concept of any programming language. Break (breaks the loop/switch) Break statement is used to terminate the current loop iteration or terminate the switch statement in which it appears Break statement can be used in the following scenarios: for loop (For loop & nested for loop) While (while loop & nested while loop) Do while (do while loop and nested while loop) Switch case (Switch cases and nested switch cases)

26. int i; for ( i= 0; i < 10; i++) { if (i == 4) { break; } printf("\n %d",i); } Output 1 2 3

27. Continue C Continue The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop . This example skips the value of 4 : int i; for ( i= 0; i < 10; i++) { if (i == 4) { continue; } printf("\n %d",i); } Output 1 2 3 5 6 7 8 9

28. Break and Continue in While Loop Break int i = 0; while (i < 10) { printf (“%d”, i ); i++; if (i == 4) { break; } }

29. Continue int i = 0; while (i < 10) { if (i == 4) { i++; continue; } printf (“%d”, i ); i++; }