Programming Applications for Engineers
CS159: Programming Application for Engineering
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Objectives
❏ To understand the basic concepts and uses of arrays
❏ To be able to define C arrays
❏ To be able to pass arrays and array elements to functions
❏ To understand the sequential search algorithm
❏ To write programs that search arrays
Chapter 8 Arrays
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8-1 Concepts
• Imagine we have a problem that requires us to read, process, and print a large number of integers. We must also keep the integers in memory for the duration of the program.
• To process large amounts of data we need a powerful data structure, the array.
• An array is a collection of elements of the same data type. • Since an array is a sequenced collection, we can refer to the elements in
the array as the first element, the second element, and so forth until we get to the last element.
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FIGURE 8-2 Ten Variables
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FIGURE 8-3 Process 10 variables
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FIGURE 8-4 An Array of Scores
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FIGURE 8-5 Loop for 10 Scores
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8-2 Using Arrays in C
In this section, we first show how to declare and define arrays. Then we present several typical applications using arrays including reading values into arrays, accessing and exchanging elements in arrays, and printing arrays.
Declaration and Definition Accessing Elements in Arrays Storing Values in Arrays Index Range Checking
Topics discussed in this section:
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FIGURE 8-6 The Scores Array
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FIGURE 8-7 Declaring and Defining Arrays
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Only fixed-length arrays can be initialized when they are defined. Variable length arrays must be initialized by inputting or assigning the values.
Note
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FIGURE 8-8 Initializing Arrays
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One array cannot be copied to another using assignment.
Note
Exercise 1 • Write a C program that:
• Declare a constant value SIZE= 10
• Declare two arrays A and B with 10 elements
• Read 10 elements in an array A of integer.
• Copy the elements of array A into another array B.
• Change the values in the array B to 100 if they are greater than 100.
• Change the values in the array B to 10 if they are less or equal to 0.
• Print the values of the original array A and the new array B as below:
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Exercise 1 - Solution
• Write a C program that: • Declare a constant value SIZE= 10
#define SIZE 10
• Declare two arrays A and B with 10 elements
int A[SIZE], B[SIZE];
• Read 10 elements in an array A of integer.
printf("Input %d elements in the array :\n", SIZE);
for (i = 0;i<SIZE;i++)
{
printf("element - %d : ", i);
scanf("%d", &A[i]);
}
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Exercise 1 - Solution
• Copy the elements of array A into another array B.
• Change the values in the array B to 100 if they are greater than 100.
• Change the values in the array B to 10 if they are less or equal to 0.
for (i = 0; i<SIZE; i++)
{
B[i] = A[i];
if (B[i] > 100)
B[i] = 100;
else if (B[i] <= 0)
B[i] = 10;
}
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Exercise 1 - - Solution
• Print the values of the original array A and the new array B as below:
printf("\nOrigin array A :\n");
for (i = 0; i<SIZE; i++)
printf("% 5d", A[i]);
printf("\n\nNew array B :\n");
for (i = 0; i<SIZE; i++)
printf("% 5d", B[i]);
printf("\n\n");
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Computer Science: A Structured Programming Approach Using C
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FIGURE 8-9 Exchanging Scores—the Wrong Way
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FIGURE 8-10 Exchanging Scores with Temporary Variable
Exercise 2 • Write a C program that:
• Declare a constant value SIZE= 12
• Declare an array A with 12 elements
• Print 5 Numbers per Line as below.
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#include <stdio.h> #include <stdlib.h> #define SIZE 12 int main() { int A[SIZE], i, linecount=0; printf("Input %d elements in the array :\n", SIZE); for (i = 0;i<SIZE;i++) {
printf("element - %d : ", i);scanf("%d", &A[i]); } for (i = 0; i < SIZE; i++) {
printf("% 5d", A[i]); linecount++; if (linecount % 5 == 0)
printf("\n"); } printf("\n\n"); system("pause"); return 0; }
Exercise 2 - Solution
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PROGRAM 8-2 Squares Array
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PROGRAM 8-3 Print Input Reversed
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PROGRAM 8-2 Print Input Reversed
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PROGRAM 8-2 Print Input Reversed
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8-3 Inter-function Communication
To process arrays in a large program, we have to be able to pass them to functions. We can pass arrays in two ways: pass individual elements or pass the whole array. In this section we discuss first how to pass individual elements and then how to pass the whole array.
Passing Individual Elements Passing the Whole Array
Topics discussed in this section:
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FIGURE 8-11 Passing Array Elements
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PROGRAM 8-4 Calculate Array Average
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PROGRAM 8-4 Calculate Array Average
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PROGRAM 8-6 Change Values in an Array
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PROGRAM 8-6 Change Values in an Array
Exercise 3: Find the output of the following code
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#include <stdio.h> #include <stdlib.h> #define SIZE 10 int f1(int a[]); int main() {
int A[SIZE] = {5,2,1,2,3,6,1,8,9,6,}, i, r; for (i = 0; i < SIZE; i++)
printf("%4d", A[i]); printf("\n"); r = f1(A); for (i = 0; i < SIZE; i++)
printf("%4d", A[i]); printf(“\nSum = %d \n",r); return 0;
} int f1(int a[]) {
int i,s = 2; for (i = 0;i < SIZE; i = i + 2) {
s = s + a[i]; a[i] = 0;
} return(s + 10);
}
Exercise 3: Find the output of the following code
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#include <stdio.h> #include <stdlib.h> #define SIZE 10 int f1(int a[]); int main() {
int A[SIZE] = {5,2,1,2,3,6,1,8,9,6,}, i, r; for (i = 0; i < SIZE; i++)
printf("%4d", A[i]); printf("\n"); r = f1(A); for (i = 0; i < SIZE; i++)
printf("%4d", A[i]); printf(“\nSum = %d \n",r); return 0;
} int f1(int a[]) {
int i,s = 2; for (i = 0;i < SIZE; i = i + 2) {
s = s + a[i]; a[i] = 0;
} return(s + 10);
}
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Chapter 8 Problems 16, 28, 29
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8-6 Searching
Another common operation in computer science is searching, which is the process used to find the location of a target among a list of objects. In the case of an array, searching means that given a value, we want to find the location (index) of the first element in the array that contains that value.
Sequential Search
Topics discussed in this section:
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FIGURE 8-27 Search Concept
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FIGURE 8-28 Locating Data in Unordered List
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FIGURE 8-29 Unsuccessful Search in Unordered List
Sequential Search • Compares each element of an array with a search key
• Just as likely that the value will be found in the first element as the last • On average, program must compare the search key with half the elements of the array
• To determine that value is not in array, program must compare the search key to every element in the array
• Works well for small or unsorted arrays
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EXERCICE 4
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• Define a function linearSearch for searching a target within an array. The function should return the position of the target if it is found in the array, otherwise the function should return -1.
Function prototype: int linearSearch(int a[], int size, int target);
• Write a main function to ask user to enter 10 values and find the position of the target 15 in the array.
Expected output:
Exercise 4 – Solution (Sequential Search)
int linearSearch(int a[], int size, int target) { // Return the position of target if it is found in the array // Return -1 if the target is not found in the array int i; for (i = 0;i<size;i++) if (a[i] == target)
return i;
return -1; }
#include <stdio.h> #include <stdlib.h> #define SIZE 10 int linearSearch(int a[], int size, int target); int main() {
int t[SIZE], search, i, a; int target = 15; printf("Enter %d integer(s)\n", SIZE); for (i = 0; i < SIZE; i++)
scanf("%d", &t[i]); a = linearSearch(t, SIZE, target); printf("position = %d \n", a); if (a != -1)
printf("%d is found in the array at position %d\n", target,a); else
printf("%d is not found in the array.\n\n", target); system("pause"); return 0;
}
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Chapter 8 Problem 36
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8-7 Two-Dimensional Arrays
The arrays we have discussed so far are known as one-dimensional arrays because the data are organized linearly in only one direction. Many applications require that data be stored in more than one dimension. One common example is a table, which is an array that consists of rows and columns.
Declaration Passing A Two-Dimensional Array
Topics discussed in this section:
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FIGURE 8-34 Two-dimensional Array
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FIGURE 8-35 Array Of Arrays
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FIGURE 8-36 Memory Layout
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FIGURE 8-37 Passing a Row
Exercise 5
• Write a program that sums the elements of a given 2D array.
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Exercise 6
• How will you calculate the average of integers in this 2-D array?
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PROGRAM 8-16 Convert Table to One-dimensional Array
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PROGRAM 8-16 Convert Table to One-dimensional Array
Square Matrix no. of rows = no. of columns
(e.g. 6 x 6 Matrix)
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FIGURE 8-39 Example of Filled Matrix
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PROGRAM 8-17 Fill Matrix
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PROGRAM 8-17 Fill Matrix
Exercise
• Write a function sum2D that takes a 2D array of integers and its number of rows as arguments, and returns their sum.
• Write a function sumRows that takes a 2D array of integers, an empty array, and its size, as arguments, and returns the sum of each row in the empty array.
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