Bài giảng Introduction to Computer Programming (C language) - Chapter 7: Arrays - Võ Thị Ngọc Châu

t by 15 customers 
 numProduct in memory 
 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 
 int numProduct[15]; 
 12 
 One-dimension arrays 
 A one-dimension array is the simplest type of 
 array in C. 
type_name variable_name[constant_expressionopt] =opt {expression_list}opt; 
Example 2: an array of 10 doubles to represent 10 positive numbers 
 positiveNumber in memory 
 2 1 3 10 8 3 4 5 9 12 
 double positiveNumber[10]; 
 13 
 One-dimension arrays 
 A one-dimension array is the simplest type of 
 array in C. 
type_name variable_name[constant_expressionopt] =opt {expression_list}opt; 
Example 3: an array of 10 elements of struct supplier to represent 
10 suppliers 
 lstSupplier in memory 
 id A C T I V E S F O R 
 value 1 2 3 8 3 4 7 2 9 6 
 struct supplier lstSupplier[10]; 14 
 Memory model of a C array 
 When defined, an array can be: 
  A global variable, 
  A local variable, 
  A static local variable, 
  A dynamic local variable,  
 It will be organized with a fixed size in an appropriate 
 corresponding memory segment (.data, .bss, stack, heap). 
 Regardless of its memory segment, an array is a group of 
 contiguous memory locations that all have the same type. 
 Array name is the address of the first location among these contiguous 
 memory locations. 
 positiveNumber in memory 
 positiveNumber is the address of 
 the first double memory location. 2 1 3 10 8 3 4 5 9 12 
 double positiveNumber[10]; 15 
Memory model of a C array 
 8 bytes8 bytes8 bytes8 bytes positiveNumber in memory 
 2 1 3 10 8 3 4 5 9 12 
 double positiveNumber[10]; 
 16 
 Memory model of a C array 
 Array name is the address of the first location among 
 these contiguous memory locations. 
 Therefore, assignment for an entire array is not valid!!! 
 a = {4, 2, 9, -8, 0}; // INVALID!!!!!!!!!!!!!! 
 17 
Memory model of a C array 
 intArray in memory 
 3 0 8 9 -2 
 int intArray[] = {3, 0, 8, 9, -2}; 
 The compiler determined the size of this 
 array based on the number of initial values 
 18 
 Access to the elements of 
 a C array 
 Element access is based on index starting 
 from 0 (zero) with name[..]. 
  Index for the first element is 0: name[0] 
  Index for the second element is 1: name[1] 
  Index for the (i+1)-th element is i: name[i] 
  Index for the n-th element is n-1: name[n-1] 
 positiveNumber in memory 
 2 1 3 10 8 3 4 5 9 12 
 positiveNumber[0] positiveNumber[5] positiveNumber[9] 
 double positiveNumber[10]; 
 19 
 Access to the elements of 
 a C array 
 Element access is based on index with name[..]. 
 intArray in memory 
 3 0 8 9 -2 
 int intArray[] = {3, 0, 8, 9, -2}; 
 20 
 Access to the elements of 
 a C array 
 Element access is based on index with name[..]. 
  What happens with intArray[-1]? 
  What happens with intArray[5]? 
 Unspecified The previous memory 
 of intArray[0] 
 values!!! The next memory of 
 intArray[4] 
 Access to the elements of 
 a C array 
 What happens if an array defined with a given size is 
 initialized with less initial values? 
 Zero-filled bytes: 0, „\0‟ 22 
 Access to the elements of 
 a C array 
 What happens if an array defined with a given size is 
 initialized with more initial values? 
Unspecified value!!! 
Not 7 in initialization!!! 
 23 
 Access to the elements of 
 a C array 
 Element access is based on index starting 
 from 0 (zero) with name[..]. 
 Each element access with name[..] plays a 
 role of a single variable of the same type. 
  Used in any relevant expressions 
 a1[0] == 2 
 a1[i] > 1 
  Used in any relevant statements 
 while (a1[2] <= 10) {} 
 a1[i] = a1[i-1] * 5; 
 24 
 Access to the elements of 
 a C array 
 How many tens have you got for your midterm exams? 
 What is your averaged grade? 
 25 
 List the frequency of each character 
 in your collection. 
 26 
Arrays of characters for strings 
 The C language has no specific data type 
 for strings. 
  Each string is considered as a one-dimension 
 array of characters ended by „\0‟. 
  A standard library for strings: 
 size_t strlen(const char *str) 
 char *strcpy(char *dest, const char *src) 
 int strcmp(const char *str1, const char *str2) 
 char *strcat(char *dest, const char *src) 
 char *strtok(char *str, const char *delim) 
 27 
Strings and Characters 
  int toupper(int c)  int ispunct(int c) 
  int tolower(int c)  int isspace(int c) 
  int isupper(int c)  int isalnum(int c) 
  int islower(int c)  int isalpha(int c) 
  int isdigit(int c) 
   
 28 
Strings and Numbers 
  double atof(const char *str) 
  int atoi(const char *str) 
  long int atol(const char *str) 
  double strtod(const char *str, char **endptr) 
  long int strtol(const char *str, char **endptr, 
 int base) 
  unsigned long int strtoul(const char *str, 
 char **endptr, int base) 
 29 
 Arrays of characters for strings 
 strCName is a string 
 defined as an array of 20 characters 
 ended with an additional character „\0‟ 
 located in memory with 21 bytes 
 C o m p u t e r P r o g r a m m i n g \0 
index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
 Number of bytes 
 in memory 
 size >= length + 1 
 Number of characters 
 in use, not counting „\0‟ 
 The compiler determined the size of this string 
 based on the number of initial characters 
 C o m p u t e r P r o g r a m m i n g \0 
index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
 Number of bytes 
 in memory 
 size >= length + 1 
 Number of characters 
 in use, not counting „\0‟ 
 The compiler determined the size of this string 
 based on the given number of elements in array 
 C P r o g r a m m i n g \0 \0 \0 \0 \0 \0 \0 
index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 
 Arrays of characters for strings 
 char strCName[20] = “C Programming”; 
 strCName is the address of the first char memory location. 
 C P r o g r a m m i n g \0 \0 \0 \0 \0 \0 \0 
index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 
 length = 13 characters in use 
 size = 20 bytes in memory 
 strCName == &strCName[0] => TRUE type value memory 
 strCName[10] == „i‟ => TRUE char „i‟ i 
 strCName[10] == “i” => FALSE char [] “i” i \0 
 0 1 
 strCName = “Programming”; => INVALID for assignment => strcpy(..) 
 strCName == “B Programming” => INVALID for comparison => strcmp(..) 
 Arrays of characters for strings 
 Enter your full name and then rewrite your name 
 as “first_name last_name” in English 
 Check if an input name is valid!! 
 34 
Full name => First_name Last_name 
Checked for a valid full name 
 35 
 Multidimensional arrays 
 In our previous example, a string is tokenized 
 into many substrings based on delimiters. 
  Input: 
 char aString[50] = “Introduction to Computer Programming”; 
  Output: 
 char Token_1[50] = “Introduction”; 
 char Token_2[50] = “to”; 
 char Token_3[50] = “Computer”; 
 char Token_4[50] = “Programming”; 
 Can we have a list of a list of  of a list? 
 Multidimensional arrays!!! 36 
 Multidimensional arrays 
 More in our real world, example 1 is: 
  A list of students 
 Each student has a list of submissions, each per chapter. 
 . Each submission includes a list of exercises to be grades. 
 For grading each exercise, we need a three-dimension array of 
 natural numbers. 
 Example 2 is: 
  A gray-scale image of size 100x100 
 Each pixel at (i, j) is a positive integer number in [0, 255]. 
 For image processing, we need a two-dimension array of 
 positive integer numbers. 
 Example 3 is related to matrices in your linear algebra 
 which are two-dimension arrays of numbers. 
 37 
Multidimensional arrays 
 A multidimensional array is an array. Each element of a 
 multidimensional array is also an array. 
 1 2 d
 type_name variable_name[size opt][size opt].. [size opt] \ 
 =opt {{{expression_list}, {}, }, {}, }opt; 
 size1, size2, , or sized: optional, if specified, a constant integer 
 expression used for a size of the array at the 1st, 2nd, , or dth 
 dimension 
 {expression_list}: optional, a list of expressions separated by 
 comma for initialized values corresponding to dimensions 
 size1*size2**sized*sizeof(type_name) bytes are allocated 
 for this array as a group of contiguous memory locations of 
 the same type. 38 
Multidimensional arrays 
char aString[4][50]: a list of many different strings from tokenization 
 39 
 Multidimensional arrays 
 Example 1: 
 Example 2: 
 Example 3: 
 Values Values Values Values Values 
 at row 1 at row 2 at row 4 at row 5 
size at size at at row 3 
dimension 1 dimension 2 
(row) (column) 40 
 Access to an element: 
 name[i1][i2][id] 
 A value of aMatrix[1][2] 
 A value of aMatrix[3][3] 
 4 bytes 4 bytes 
memory 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
index 
 [0][0] [0][1] [0][2] [0][3] [1][0] [1][1] [1][2] [1][3] [2][0] [2][1] [2][2] [2][3] [3][0] [3][1] [3][2] [3][3] [4][0] [4][1] [4][2] [4][3] 
 Access via index at each dimension is enabled and indices start at 0 for all dimensions. 
 Array name is the address of the first memory location: aMatrix == &aMatrix[0][0] 
Multidimensional arrays 
 Size of the first dimension is determined by 
 the compiler based on the initial values. 
 Some elements have initial values. 
 The rest will get zeros. 
 One-dimensional array 
 42 
 Multidimensional arrays 
 Generate a square matrix with a unit diagonal 
  Output square matrix: nxn 
 Print a transpose of a square matrix 
  Input square matrix: nxn 
  Output square matrix: nxn 
 Compute a dissimilarity matrix of n objects in 
 a 3D space input from the user 
  Input data matrix: nx3 
  Output dissimilarity matrix: nxn 
 43 
Generate a square matrix 
with a unit diagonal 
 a[i][i] = 1; 
 a[i][n-1-i] = 1; 
 44 
 Print a transpose 
 of a square matrix 
In the standard library: 
- void srand(): initialize the random number generator used 
by the function rand() based on the system time 
- int rand(): generate a random number in the range of 0 to 
RAND_MAX (32767) 
In the standard library: 
- time_t: a type for storing the calendar time 
- time_t time(time_t *timer): calculate the current calendar 
time and encode it into time_t format 
Compute a dissimilarity matrix 
of n objects in a 3D space input 
from the user 
Compute a dissimilarity matrix 
of n objects in a 3D space input 
from the user 
 Passing arrays to functions 
 Recall 
 int a[10] = {2, 3, -1, 0, 4, 7, 9}; 
 a, array name, is the address of the first int memory location. 
 Access to a[5] returns an 
 2 3 -1 0 4 7 9 0 0 0 int value: 4. 
index 0 1 2 3 4 5 6 7 8 9 
 int b[3][5] = {{2, 3, -1, 0, 4}, {7, 9}, {6, 11, -2, 5}}; 
 b, array name, is the address of the first int memory location. 
 Access to b[2] returns 
 the address of b[2][0] 
 for the third row. 
 2 3 -1 0 4 7 9 0 0 0 6 11 -2 5 0 
index [0][0] [0][1] [0][2] [0][3] [0][4] [1][0] [1][1] [1][2] [1][3] [1][4] [2][0] [2][1] [2][2] [2][3] [2][4] 
 Access to b[0][2] 
 returns an int value: -1. 48 
 Passing arrays to functions 
 Pass a value of an element at index i of a one-dimension array a 
 to functions Value passing - unchanged 
  Call to function func: func(a[i], ) 
 Pass all the values of the elements of a one-dimension array a 
 to functions 
 Address passing - changeable 
  Call to function func: func(a, ) 
 Pass a value of an element at indices i and j of a two-dimension 
 array b to functions 
 Value passing - unchanged 
  Call to function func: func(b[i][j], ) 
 Pass a row at index i of a two-dimension array b to functions 
  Call to function func: func(b[i], ) Address passing - changeable 
 Pass all the values of the elements of a two-dimension array b 
 to functions Address passing - changeable 
  Call to function func: func(b, ) 
 49 
 Find the greatest number in 
Passing arrays anto array functions of integer numbers 
 getMax(a[i-1], a[i]) ? 
 getMaxA(a, 10) ? 
 getMaxA(b[0], 5) ? 
 getMaxA(b[i], 5) ? 
 getMaxM(b, 4, 5) ? 
 50 
 Find the greatest number in 
 an array of integer numbers 
 It is necessary to specify the actual number 
 of elements present in the array 
It is not necessary to specify 
the size of the array. 
 It is necessary to specify the actual number 
 of elements present in the array at each 
 dimension 
 It is required to specify the 
 size of each non-first 
 dimension of the array. 
 51 
 Change the greatest numbers in 
 an array of integer numbers to 
 RAND_MAX 
 chgMaxA(a, 10, RAND_MAX) ? 
 chgMaxM(b, 4, 5, RAND_MAX) ? 
 52 
 Change the greatest numbers 
 in an array of integer 
 numbers to RAND_MAX 
An element nums[i] is changed. This change is 
recorded in the memory locations of the array 
during the execution of the called function. 
Changes remain after the execution of the 
called function. 
 An element nums[i][j] is changed. This change 
 is recorded in the memory locations of the 
 array during the execution of the called 
 function. Changes remain after the execution of 
 the called function. 
 53 
Put them all together 
 Problem 1: String Filtering 
  Input: a string from a user obtained with gets() 
 “1. Today is Monday, isn‟t it? 234 - go 2 school.”\n 
  Filtering: remove all the digits and redundant 
 spaces („ ‟, „\t‟) by keeping and/or replacing with 
 a single whitespace „ ‟ 
  Output: a string with no digit and each word 
 separated from each other by a single 
 whitespace „ ‟ 
 “. Today is Monday, isn‟t it? - go school.” 
 54 
Put them all together 
 Problem 2: Statistical Descriptive Info. 
  Input: a one-dimension array of n integer 
 numbers with n is a natural number given by a 
 user 
 int a[10] = {1, -3, 9, 0, 2, 8, 9, 4, 7, 6}; 
  Calculation: calculate the statistical descriptive 
 information about the input n integer numbers: 
 min, median, mean, mode, max 
  Output: min, median, mean, mode, max 
 min = -3; median = (4+6)/2 = 5.0; 
 mean = 4.3; mode = 9; max = 9 
 Note: sorting is needed! 55 
Put them all together 
 Problem 3: Matrix Multiplication 
  Input: two matrices m1 (r1xc1) and m2 (r2xc2) 
 of floating-point numbers 
  Calculation: multiply m1 by m2 
  Output: a resulting matrix m3 (r1xc2) 
 2 4 0 1 
 m1 1 2 1 0 
 0 2 3 1 
 7 0 
 0 2 m1xm2 
 1 1 m3 3 5 
 m2 
 1 1 4 1 
 3 0 56 
Summary 
 An array is a group of continuous memory 
 locations of the same type. 
  Its size is unchanged during its existence. 
  It can be considered as a group of individual 
 variables of the same type. 
 Used in any relevant expressions, statements, functions 
 Definition can be done with initialization. 
 Index-based access starts at zero. 
 One-dimension vs. multidimensional arrays 
 Strings are special one-dimension arrays of 
 characters ended by „\0‟. 
 57 
Chapter 7: Arrays 
 58