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Introduction to Computer Algorithmics and Programming Ceng 113

Introduction to Computer Algorithmics and Programming Ceng 113. Custom Data Types “Unions, Enumaration”. Unions. A union is a memory location that is shared by two or more different variables, generally different types, at different times . Its general form is; union tag{

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Introduction to Computer Algorithmics and Programming Ceng 113

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  1. Introduction to Computer Algorithmics and ProgrammingCeng 113 Custom Data Types “Unions, Enumaration”

  2. Unions A union is a memory location that is shared by two or more different variables, generally different types, at different times. Its general form is; union tag{ type variable_name; type variable_name; …. } union_variables;

  3. Unions union u_type { int i; char ch; } ; union u_type c; In union cnvt, both integer i and character ch share the same memory location. Byte 0 Byte 1 c.i = 10; ch i

  4. Unions union DWORD { unsigned char byte; unsigned int word; unsigned long dword; }; ... Union DWORD a; a.byte a.word a.dword

  5. Unions union DBL_FORM { double n; unsigned char s[8]; }; ... Union DBL_FORM x; x.s[0] x.s[1] x.s[2] x.n x.s[0]...x.s[7] x.s[7]

  6. Unions struct WORD { unsigned char low_byte; unsigned char high_byte; }; union WORD_FORM { unsigned int x; struct WORD y; }; union WORD_FORM wf; wf.y.low_byte = 0x12; wf.y.high_byte = 0x34; printf(“%x \n”, wf.y); wf.y.low_byte 0x12 wf.x 0x34 wf.y.high_byte

  7. Unions #include <stdio.h> #include <stdio.h> #include <string.h> union pw { unsigned int i; char ch[2]; }word; void main(void) { word.i = 512; // 2^8 = (00000010 00000000)2 printf("\n word.ch[0] = %d \n", word.ch[0]); printf("\n word.ch[1] = %d \n", word.ch[1]); }

  8. Enumaration An enumaration is a set of named integer constants that specify all the legal values a variable of that type may have. The general form is; enum tag {enumaration list } variable_list; Example; enum coin { penny, nickel, dime, quarter, half_dollar, dollar}; enum coin money; The key point to understand about an enumaration is that each of the symbols stands for an integer value. The value of the first enumaration symbol is 0. Therefore; printf(“%d %d”, penny, dime); displays 0 and 2.

  9. Enumaration enum coin { penny, nickel, dime, quarter=100, half_dollar, dollar}; Now, the values of these symbols are; penny 0 nickel 1 dime 2 quarter 100 half_dollar 101 dollar 102

  10. Enumaration enum coin { penny, nickel, dime, quarter, half_dollar, dollar}; enum coin money; … switch(money) { case penny: printf(“penny”); break; case nickel: printf(“nickel”); break; case dime: printf(“dime”); break; case quarter:printf(“quarter”); break; case half_dollar:printf(“half_dollar); break; case dollar: printf(“dollar”); } enum coin { penny, nickel, dime, quarter, half_dollar, dollar}; enum coin money; .. char name[ ]= { “penny”, “nickel”, “dime”, “quarter”, “half_dollar”, “dollar” }; … printf(“%s”, name[money]); Enum_Sample.cpp

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