- searching - sorting. given: the array the search target: the array element value we are looking...

ARRAYS- SEARCHING

- SORTING

Given:The arrayThe search target: the array element value we

are looking for Algorithm:

Start with the initial array element (subscript 0)Repeat until there are more array elements

(subscript = array size – 1) Compare the target with the current element

1. LINEAR SEARCH

Dr. Soha S. Zaghloul 2

2. LINEAR SEARCH – ILLUSTRATED


gpa [0] 4.52

gpa [1] 3.02

gpa [2] 2.25

… …

… …

gpa [30] 3.45

gpa [31] 2.99

… …

… …

gpa [48] 4.32

gpa [49] 4.82

gpa[0]= = target?

gpa[1]= = target?

gpa[2]= = target?

gpa[30]= = target?

gpa[31]= = target?

gpa[48]= = target?

gpa[49]= = target?

3. LINEAR SEARCH USING FOR - CODE


#include <stdio.h>int main (void){ double target, gpa[50]; int i; int index; // position of the found element int found = 0; // flag initially set to 0 // array initialization for (i = 0; i < 50; i++) { printf (“Enter element value> “); scanf (“%f”, &gpa[i]); } // end for // Get the search target printf (“Enter the value you are looking for> “); scanf (“%f”, &target); // Compare all array elements with the target for (i = 0; i < 50; i++) if (gpa[i] == target) { index = i; //store the position found = 1; // set flag to 1 } // end if if (found) // if (found == 1) printf (“Target %f is found at position %d \n”, target, index); else printf (“Target not found”); return 0;} // end main

The loop ends when the counter reaches the end of the array

Why going through the whole array if the target is found?

It is better to update the code fragment in the previous slide as follows:

4. LINEAR SEARCH USING WHILE


int i = 0;int found = 0; while ((!found) && (i < 50)) { if (gpa[i] == target) break; else i++; } // end while

int i = 0;int found = 0; while ((!found) && (i < 50)) { if (gpa[i] == target) found = 1; else i++; } // end while

Since we need to perform the comparison at least once (with gpa[0]), then linear search can also be implemented using do…while.

The core code is as follows:

5. LINEAR SEARCH USING DO…WHILE


int i = 0;int found = 0; do { if (gpa[i] == target) break; else i++; } while ((!found) && (i < 50))

int i = 0;int found = 0; do { if (gpa[i] == target) found = 1; else i++; } while ((!found) && (i < 50))

If you want to swap (exchange) the values of two variables, you need a third variable.

For example, assume the following:x = 5y = 8

To swap the values of x and y, we will use a temporary variable temp as follows:

6. SWAPPING


temp = x; //temp=5 x=5 y=8x = y; //temp=5 x=8 y=8y=temp; //temp=5 x=8 y=5

Assume the first element is the minimum value

Go through all the array and find if there is a lesser value

If there is a lesser value put it in minimum

7. FINDING MINIMUM ELEMENT


int i; // counterint array_size; // size of the arrayint minimum; // to hold the minimum value of the arrayminimum = x[0]; // assume x[0] is the minimum value in the arrayfor (i = 0; i < array_size; i++) if (x[i] < minimum) minimum = x[i];

8. FINDING MINIMUM ELEMENT - TRACING


int i, array_size, minimum; minimum = x[0]; for (i = 0; i < array_size; i++) if (x[i] < minimum) minimum = x[i];

x[0] x[1] x[2] x[3]

74 45 83 16

minimum i++ i < array_size? x[i] < minimum?

x[0] = 74: initial value

0: initial value1 1 < 4? True x[1] <

minimum?45 < 74? True

array_size = 4

45 2 2 < 4? True X[2] < minimum?83 < 45? False

45 3 3 < 4? True X[3] < minimum?16 < 45? True

16 4 4 < 4? False Exit from loop

Sorting an arrays in ascending order is to arrange it such that:X[0] < x[1] < x[2] < x[3] < …..

Example:Assume that we have the following array

After being sorted the array will be as follows:

9. SORTING ARRAYS


x[0] x[1] x[2] x[3]

74 45 83 16

x[0] x[1] x[2] x[3]

16 45 74 83

Let current position = 0 Find the minimum element in the array Swap with the current position Move to the next current position (current+

+) Repeat the same steps until you reach the

end of the array

10. SORTING ARRAYS – ALGORITHM


11. SORTING ARRAYS – ILLUSTRATED


x[0] x[1] x[2] x[3]

74 45 83 16

x[0] x[1] x[2] x[3]

16 45 83 74

1st iteration

current = 0 Minimum element in the array x[0] to x[3] = 16 index_min = 3 (subscript) Swap x[current] with x[index_min]

2nd iteration

current = 1 Minimum element in the array x[1] to x[3] = 45 index_min = current No swap needed

11. SORTING ARRAYS – ILLUSTRATED (CNT’D)


x[0] x[1] x[2] x[3]

16 45 83 74

x[0] x[1] x[2] x[3]

16 45 74 83

3rd iteration

current = 2 Minimum element in the array x[2] to x[3] = 74 index_min = 3 (subscript) Swap x[current] with x[index_min]

4th iteration

current = 3 Minimum element in the array x[3] to x[3] = 83 index_min = current No swap needed

The last iteration is not needed since only one element is left

12. SORTING ARRAYS – CODE


#include <stdio.h>int main (void){// declaration partint x[4], i, current, minimum, index_min, temp;

// initialize the arrayfor (i = 0; i < 4; i++) { printf (“enter x[%d]”, i); // displayed as enter x[0] in the 1st iteration scanf (“%d”, &x[i]); } // end for i for (current = 0; current < 3; current++) { // find minimum element in the subarray starting from current // store the subscript of the minimum element (index_min) // if (current != index_min) swap } // end for current} //end main

12. SORTING ARRAYS – CODE (CNT’D)


for (current = 0; current < 2; current++) // limit = array_size - 2 { minimum = x[current]; // assume x[current] is the minimum index_min = current; // hold the corresponding subscript // find the minimum value in the sub-array starting from x[current] for (i = current; i < 3; i++) { if (x[i] < minimum) { minimum = x[i]; index_min = i; // store the subscript of the minimum element } // end if (x[i] < minimum) } // end for(i = current;… // swap if index_min != current else do nothing if (index_min != current) { temp = x[index_min]; x[index_min] = x[current]; x[current] = temp; } // end if (index_min != current) } // end for (current = 0;…} //end main

13. SELF-CHECK EXERCISES


Write a complete program to take two numerical lists of the same length 20. Then, the program stores the lists in arrays x and y; each of which is of length 20. Then, the program should do the following:

− Store the product of corresponding elements of x and y in a third array, z, also of size 20.

− Display the arrays x, y, z in a three-column table.− Compute and display the square root of the sum of the items in z.

Update the above program so that to use a sentinel value to end data entry. The arrays x, y and z are of length 5. Make up your own data and trace your program in the following cases:

- The user entered exactly 5 numbers in each list- The user entered 6 numbers in each list- The user entered 3 numbers in each listMake necessary changes to your program accordingly.

13. SELF-CHECK EXERCISES


Write a complete program that performs the following to an array x of type int and length 20:- Fill the array with 20 values- Finds and displays the largest value in the array- Finds and displays the subscript of the largest value in the array

Write an interactive program that stores a word in an array of characters. The program asks the user to guess a letter. The program should then check if this letter is in word or not. An appropriate message is displayed accordingly. The program ends after 3 times of incorrect guesses or when the user enters a sentinel value.

- searching - sorting. given: the array the search target: the array element value we are looking...

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