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Introduction to Computer Algorithmics and Programming Ceng 113

Introduction to Computer Algorithmics and Programming Ceng 113. Arrays and Strings. Arrays. An array is a collection of variables of the same type that are referenced by a common name. A specific element in an array is accesses by an index . All arrays placed a continuous memory areas.

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Introduction to Computer Algorithmics and Programming Ceng 113

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  1. Introduction to Computer Algorithmics and ProgrammingCeng 113 Arrays and Strings

  2. Arrays • An array is a collection of variables of the same type that are referenced by a common name. • A specific element in an array is accesses by an index. • All arrays placed a continuousmemory areas. • Arrays may have one to several dimensions.

  3. Single Dimention Arrays The general decleration form is; type var_name[size]; type ; declares the base type of the array. size ; defines how many elements the array will hold. The amount of storage required to hold an array is; total bytes = size_of_type * size_of_array Example; double balance[100];would be: sizeof(double) * 100, which is usually 8*100 bytes

  4. * Single Dimension Arrays void main(void) { int x[10]; /* this reserves 10 integer elements */ int t; for (t=0; t<10; t++) x[t]=t; for(t=0; t<10; t++) printf("\n x[%d]= %d", t, x[t]); } Array_One_Dim.C

  5. Example #1 Determine the existence of the common elements for two arrays: found = 0; for (i = 0; i < n && !found; i++) for (j = 0; j < m && !found; j++) if (a[i] == b[j]) found = 1; if (found) /* got one: a[i-1] == b[j-1] */ ... else /* didn't find any common element */ ...

  6. Example #2 #include <stdio.h> // determine the biggest element of an array. int a[10]={100, 140, 7, 190, 5, 1, 17, 390, 245,112}; void main() { int max, i; max= a[0]; for (i=1; i<10; ++i) if (a[i] > max) max = a[i]; printf(“\n The max element: %d \n”, max); }

  7. Generating a Pointer to an Array How array x appears in memory if it starts at memory location 1000 : We can generate a pointer to the first element of an array without any index. Example; char x[10]; char *p; p = x;

  8. Passing One-Dimension Arrays to Functions • In C, you cannot pass entire array as an argument to a function. • However, we can pass a pointer to an array to a function by specifying the array’s name without an index. func1(int *x) /* pointer */ { .... } void main(void) { int i[10]; func1(i); .... } func1(int x[10]) /* sized array */ { .... } func1(int x[ ]) /* unsized array */ { .... }

  9. String Most common one dimension array in C is string, which is simply an array of characters terminated by a null. ( ‘\0’ ). Therefore, we need to declare character arrays to be one character longer than the largest string that they are to hold ‘\0’. Examples; If we want to hold 10 characters in the string s, we can define this array as: char s[10]; char s[10] = {‘E’, ‘x’, ‘a’, ‘m’, ‘p’, ‘l’, ‘e’, ‘\0’}; char s[10] =“Example”;

  10. String C does not have a string data type, it allows string constants. A string constant is a list of characters in double quotes. Example; “hello there”

  11. Example #3 #include <stdio.h> // the length of the string? void main() { int i=0; char s[50]; printf(“\n String: “); gets(s); while (s[i]) // means while (s[i] != 0) ++i; printf(“\n The length of the string: %d”, i); }

  12. Example #4 ? include <stdio.h> void main() { char s[30], temp; int n, j; printf(“\n String:”); gets(s); n=strlen(s); for (j=0; j<n/2; ++j) // reverse the string! { temp= s[n-j-1]; s[n-j-1]= s[j]; s[j] = temp; } puts(s); }

  13. Example #5 #include <math.h> float point_a[2]; /* array of lat/long positions */ float point_b[2]; /* array of lat/long positions */ float distance; /* distance between point a/b (computed */ float sqrt_of_distance; /* square root of distance (computed) */ int main() { point_a[0] = 43.0; point_a[1] = 13.0; point_b[0] = 59.0; point_b[1] = 19.0; distance = (point_b[0] + point_b[1]) - (point_a[0] + point_a[1]); sqrt_of_distance = sqrt(distance); printf("Point A: %f/%f\n", point_a[0], point_a[1]); printf("Point B: %f/%f\n", point_b[0], point_b[1]); printf("Distance: %f\n", distance); printf("Square root of distance: %f\n", sqrt_of_distance); return (0); }

  14. String Manipulation Functions • strcpy(s1, s2) Copies s2 to s1. • strcat(s1, s2) Concatenates s2 to the end of s1. • strlen(s1) Returns the length of s1. • strcmp(s1, s2) if s1 and s2 are same, return 0 (FALSE). if s1 < s2, return negative value. if s1 > s2, return positive value. • strchr(s1, ch) Return a pointer to the first occurrence of ch in s1. • strstr(s1, str) Return a pointer to the first occurrence of s2 in s1. These functions use the standart header file STRING.H.

  15. Example #5 * #include <stdio.h> #include <string.h> void main(void) { char s1[80], s2[80]; gets(s1); gets(s2); printf(“lenghs: %d %d \n”, strlen(s1), strlen(s2)); if (!strcmp(s1, s2)) printf(“The string are equal \n”); strcat(s1, s2); printf(“%s \n”, s1); strcpy(s1, “This is a test. \n”); puts(s1); if(strchr(“hello”, ‘e’)) printf(“e is in hello \n”); if(strstr(“hi there”, “hi”)) printf(“found hi \n”); } String_Functions.C

  16. Two-Dimensional Arrays C supports multidimensional arrays. Example; To declare two dimensional integer array d of size 10 , 20: int d[10][20]; To access point 1,2 of array d ; d[1][2]

  17. * Two-Dimensional Arrays Second Index Example; #include <stdio.h> void main(void) { int t, i, num[3][4]; for(t=0; t<3; ++t) for(i=0; i<4; ++i) num[t][i]=t*4+i+1; /* now print the array */ for((t=0; t<3; ++t) { for(i=0; i<4; ++i) printf(“%3d “, num[t][i]); printf(“\n”); } } First Index The number of bytes of memory to hold this array is; bytes=size of first index * size of second index * size_of_basetype Array_Two_Dim.C

  18. Two-Dimensional Arrays When a two dimentional array is used as an argument to a function, only a pointer to the first element is passed, and we must define the length of the second dimension. C compiler needs to know the length of each row. If the length of the rows is not known, the compiler cannot determine where the second row begins. Example; void main(void) { int x[5][10]; func1(x); ... } func1 (int x[ ] [10]) { .... }

  19. Example #6 #include <stdio.h> #define ROW 5 #define COL 2 void main() { int a[ROW][COL]={10, 20, 30, 40, 50, 60, 70, 80, 90, 100}; int b[ROW][COL]={5, 10, 15, 20, 25, 30, 35, 40, 45, 50}; int c[ROW][COL], i, j; for (i=0; i<ROW; ++i) for (j=0; j<COL; ++j) { c[i][j]=a[i][j] + b[i][j]; printf(“c[%d][%d] = %d\n”, i, j, c[i][j]); } }

  20. * Sample Program #7 • Use two dimensional array to store the numeric grade for each student in a teacher’s classes. • The program assumes that the teacher has three classes and a maximum of 10 students per class. • Write these functions; • Main function to control flow of the program • A function to enter all grades for each class • A function to read a grade from screen • A function to display all grades to screen Pgm:Array_Two_Dim_Grades.C

  21. /* Enter the student's grades. */ void enter_grades(void) { int t, i; for(t=0; t<CLASSES; t++) { printf("Class # %d:\n", t+1); for(i=0; i<GRADES; i++) grade[t][i]=get_grade(i); } } /* Read a grade. */ get_grade(int num) { char s[80]; printf("enter grade for student # %d:\n", num+1); gets(s); return(atoi(s)); } /* Display grades. */ void disp_grades(int g[][GRADES]) { int t,i; for(t=0; t<CLASSES; t++) { printf("Class # %d : \n", t+1); for(i=0; i<GRADES; i++) printf("Student # %d is %d \n", i+1, g[t][i]); } } Sample Program – V.1 #include <stdio.h> #include <ctype.h> #include <stdlib.h> /* A simple student grades database */ #define CLASSES 2 #define GRADES 3 int grade[CLASSES][GRADES]; void enter_grades(void); int get_grade(int num); void disp_grades(int g[][GRADES]); void main(void) { char ch, str[80]; for( ; ; ){ printf("(E)nter grades\n"); printf("(R)eport grades\n"); printf("(Q)uit\n"); gets(str); ch = toupper(str[0]); switch(ch) { case'E': enter_grades(); break; case 'R': disp_grades(grade); break; case 'Q': exit(0); } } }

  22. /* Enter the student's grades. */ void enter_grades(int *p) { int t, i; for(t=0; t<CLASSES; t++) { printf("Class # %d:\n", t+1); for(i=0; i<GRADES; i++) *(p + (t*GRADES) + i) = get_grade(i); } } /* Read a grade. */ get_grade(int num) { char s[80]; printf("enter grade for student # %d:\n", num+1); gets(s); return(atoi(s)); } /* Display grades. */ void disp_grades(int g[ ][GRADES]) { int t,i; for(t=0; t<CLASSES; t++) { printf("Class # %d : \n", t+1); for(i=0; i<GRADES; i++) printf("Student # %d is %d \n", i+1, g[t][i]); } } Sample Program – V.2 #include <stdio.h> #include <ctype.h> #include <stdlib.h> #define CLASSES 2 #define GRADES 3 void enter_grades(int *p); int get_grade(int num); void disp_grades(int g[][GRADES]); void main(void) { char ch, str[80]; int grade[CLASSES][GRADES]; for( ; ; ){ printf("(E)nter grades\n"); printf("(R)eport grades\n"); printf("(Q)uit\n"); gets(str); ch = toupper(*str); switch(ch) { case'E': enter_grades(grade[0]); break; case 'R': disp_grades(grade); break; case 'Q': exit(0); } } }

  23. /* Enter the student's grades. */ void enter_grades(int p[][GRADES]) { int t, i; for(t=0; t<CLASSES; t++) { printf("Class # %d:\n", t+1); for(i=0; i<GRADES; i++) p[t][i]=get_grade(i); } } /* Read a grade. */ get_grade(int num) { char s[80]; printf("enter grade for student # %d:\n", num+1); gets(s); return(atoi(s)); } /* Display grades. */ void disp_grades(int g[][GRADES]) { int t,i; for(t=0; t<CLASSES; t++) { printf("Class # %d : \n", t+1); for(i=0; i<GRADES; i++) printf("Student # %d is %d \n", i+1, g[t][i]); } } Sample Program – V.3 #include <stdio.h> #include <ctype.h> #include <stdlib.h> #define CLASSES 2 #define GRADES 3 void enter_grades(int p[][GRADES]); int get_grade(int num); void disp_grades(int g[][GRADES]); void main(void) { char ch, str[80]; int grade[CLASSES][GRADES]; for( ; ; ){ printf("(E)nter grades\n"); printf("(R)eport grades\n"); printf("(Q)uit\n"); gets(str); ch = toupper(*str); switch(ch) { case'E': enter_grades(grade); break; case 'R': disp_grades(grade); break; case 'Q': exit(0); } } }

  24. Example #8 #include <stdio.h> #define MAX 100 #define LEN 80 char text[MAX][LEN]; /* A very simple editor */ void main(void) { int t, i, j; printf("Enter an empty line to quit. \n"); for(t=0; t<MAX; t++) { printf("%d: ", t); gets(text[t]); if (!*text[t]) break; } for(i=0; i<t; i++) { for(j=0; text[i][j]; j++) putchar(text[i][j]); putchar('\n'); } } Pgm:Array_Of_String.C

  25. Multidimensional Arrays C allows arrays of more than two dimensional and the exact limit is determined by the compiler. Arrays of three or more dimensions are not often used because of the amount of the memory required. General declaration is; type name[a][b][c]...[z]; Example; int m[4][3][6][5]; Required space is (4*3*6*5*2=720 bytes), A function func1() that receives m, like this: func1(int d[ ][3][6][5]) { ... }

  26. Indexing Pointers • An array name without an index is a pointer to the first element in the array. • Any pointer variable can be indexed an array. Example; int *p, i[10]; p=i; i[5] =100; /* assign using index */ *(p+5)=100; /* assign using pointer arithmetic*/ Both assignment place the value 100 in the sixth element of array. For multidimentional arrays; a[j][k] = *(a+(j*row_length)+k) i[9] i[8] p+9 p+2 i[2] i[1] i[0] p=i

  27. Sample // This program is copied one string to another and use pointers. # include <stdio.h> # include <string.h> void string_copy(char *source, char *dest); void main () { char str_from[80], str_to[80]; gets(str_from); str_to[0]='\0'; string_copy(str_from, str_to); puts(str_to); } void string_copy(char *source, char *dest) { while ((*dest++ = *source++) != '\0'); }

  28. Array Initialization The general form is; type_specifier array_name[size1][size2]..[sizeN]={value_list}; int i[10] = {1,2,3,4,5,6,7,8,9,10}; This means i[0] have the value 1 and i[9] have the value 10. char array_name[size] = “string”; char str[9] =“I like C”; char str[9] = {‘I’,’ ‘,’l’,’i’,’k’,’e’,’ ’,’C’,’\0’}; All strings in C end with a null (‘\0’).

  29. Exercise #1 Sample-Array () Read 5 integers from the standard input and output them in reverse order. Pre define array, constants and local variables and initialize them. Post display the array elements in reverse order. Returnnull. Sample-Array() 1. size = 5 2. table will be included the numbers of element which is described in size. 3. k = 0 4. loop ( k < size) 1. read table[k] 2. k = k + 1 5. k = size-1 6. loop ( k >= 0) 1. display table[k] 2. k = k - 1 7. return null end pgm

  30. Exercise #1 #include <stdio.h> void main() { const int size = 5; int table[size]; int k; printf("\n Read the table values. \n"); for (k=0; k<size; k++) { printf("\n table[%d]=", k); scanf("%d", &table[k]); } printf("\n Display the array values in reverse order.\n"); for (k=size-1; k >=0; k--) printf("\n table[%d]= %d",k,table[k]); }

  31. Exercise #2 • Write a pseudocode algorithm and its function in C which returns true if the string parameter is a palindrome. A palindrome is any “word” which is the same forward and backward, e.g. “radar”, “noon”, “20022002”, .. The function should return false if the argument is not a palindrome. Assume the prototype is bool isPalindrome(char a[ ]); Assumption: a. There is no need for temporary arrays. The space in the arrays passed as parameter is sufficient. b. These functions can be written in eighter array-style or pointer style.

  32. Exercise #2 Program: bool isPalindrome(char a[ ]); Pre: Send a string which will be checked the polindrom specification. Post: Check the string true value if the string is polindrom. Return: If the string is polindrom, the return value is “True” otherwise “False”. 1. a_length = Length(a) 2. index_1 = 0, index_2=a_length - 1 3. while (a[index_1] = = a[index_2] AND (index_1 != index_2) 3.1 index_1++ 3.2 index_2-- 4. if index_1 == index_2 then return(true) else return(false) 5. end isPolindrome

  33. Exercise #2 bool isPolindrome(char a[ ]) { int i = 0, j; j=strlen(a) – 1; while ((a[i]==a[j]) && (i !=j)) { i++; j--; } if (i = = j) return True; else return False; }

  34. Exercise #3 • Any positive integer i can be expresses as i=2nk, where k is odd, that is, as a power of 2 times an odd number. We call n the exponent of 2 in i. For example, the exponent of 2 in 40 is 3 (bacause 40 = 23.5). Write a pseudocode algorithm and the code in C.

  35. Exercise #3 Program : find_2nk Pre: Take an odd integer value from user and set i . Post: Calculate 2nk = i Return: Print the n and k values. • Take an integer value and set i. • division=i and count=0 • Loop until division is odd • division = division/2 • count = count + 1 • Display i = 2count.division • End find_2nk

  36. Exercise #3 #include <stdio.h> #include <math.h> main() { int number, i, n=0; scanf(“%d”, &number); i=number; while (!(mod(i,2)) { n++; i=i/2; } printf (“%d is equal to %d power of 2 and multiply by %d”, number, n, i); }

  37. Exercise #4 /* Vowel Detection - is this letter a vowel */ #include <stdio.h> int main() { char vowels[10] = "AaEeIiOoUu"; int is_vowel = 0; char line[100]; int counter = 0; int j; printf("Enter a string: "); gets(line); while(line[counter] != '\0') { for (j=0; j<=10; j++) { if ( line[counter] == vowels[j]) { is_vowel = 1; break; } } if(is_vowel == 0) printf("%c is a consonant\n", line[counter]); if(is_vowel == 1) { printf("%c is a vowel\n", line[counter]); is_vowel = 0; } ++counter; } return (0); }

  38. Exercise #5 #include <stdio.h> #include <ctype.h> /* includes toupper() */ /* Program to compare 2 strings (but NOT case-sensitive) using user-defined function "stricmp()" */ int stricmp(char s1[100], char s2[100]); int main(){ char words[6][20]={"Word","wOrd","box","book","steve","steven"}; int test, i; for (i=0; i<6;i+=2) { test=stricmp(words[i],words[i+1]); printf("\n%s and %s ",words[i],words[i+1]); if (test==0) printf("are the same\n"); else {printf("are not the same"); printf("\nThe 1st different letters have int diff of %d\n",test); } } /* end of for loop */ return 0; } int stricmp(char s1[100], char s2[100]) { int diff=0, i=0; while(!(s1[i]=='\0' || s2[i]=='\0')) /* stop if one string ends */ {if (s1[i]!=s2[i]) diff=toupper(s1[i]) - toupper(s2[i]); /* if letters different set int diff. */ i++;} if (diff==0 && !(s1[i]=='\0' && s2[i]=='\0')) diff=s1[i]-s2[i]; /* If words are the same so far, check one isn't longer than the other */ return (diff); }

  39. Next Course • Pointers

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