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Understanding Memory Representation and Data Types in C Programming

This lecture from the ECS 30 course covers essential concepts in C programming, focusing on memory representation, data types, and basic operations. It includes topics such as variable declaration, the usage of printf and scanf, as well as the representation of integers and characters in binary, decimal, and hexadecimal forms. The significance of memory cells and addresses is also explored, providing an in-depth understanding of how data is stored and manipulated within a computer's architecture.

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Understanding Memory Representation and Data Types in C Programming

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  1. ecs30 Winter 2012:Programming and Problem Solving#02: Chapters 1~2 Dr. S. Felix Wu Computer Science Department University of California, Davis http://www.cs.ucdavis.edu/~wu/ wu@cs.ucdavis.edu ecs30 winter 2012 Lecture #02

  2. #include <stdio.h> int main () { intx; /* declare x */ x = 1; printf("Hello world %d\n", x); return 0; }// main() ecs30 winter 2012 Lecture #02

  3. ecs30 winter 2012 Lecture #02

  4. printf("Hello world %d\n", x); scanf(“%lf”, &miles); Try this yourself – intx = 999; printf("Hello [%d %d]\n", x, &x); ecs30 winter 2012 Lecture #02

  5. Do I need to know exactly where to store/save the value of the variable “miles”? ecs30 winter 2012 Lecture #02

  6. Memory Cell Concept Again ecs30 winter 2012 Lecture #02

  7. “Address” • Linguistics in C programming Language Where is THIS really located on my device? Then, we need a way to represent “address”! ecs30 winter 2012 Lecture #02

  8. “Address” • 32 bits or 64 bits address 01101001 10110001 11100000 10100111 0x69b1e0a7 ecs30 winter 2012 Lecture #02

  9. Information Representation: We need Memory to store both Programs/Data. But How? bit: 0/1 physical memory. (BInary digiT) byte: 8 bits word: 32 bits Numbers (Decimal/Binary/Hexadecimal): How do we use bits to represent an integer. 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ===> Decimal 0, 1 ===> Binary 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f ===> Hexadecimal ecs30 winter 2012 Lecture #02

  10. Numbers: Base: 10, 2, 16 Binary {0,1} 0,1,2,3,4,5,6,7,8,9, 10,11, 0,1,2…,10,11,12,…99,100,101,102,… 0,1,10 (2), 11(3), 100 (4), 101(5), 110(6), 4 2 1 22, 21, 20 1 0 0 1 0 + 1 1 0 ecs30 winter 2012 Lecture #02

  11. 0+1 = 1 1 20 1+1 = 10 2 21 10+1 = 11 3 11+1 = 100 4 22 100+1 = 101 5 101+1 = 110 6 110+1 = 111 7 111+1 = 1000 8 23 9 = 1+8 0001 1000 1001 001 010 100 111 001 100 101 7=1+2+4 5 = 1 + 4 ecs30 winter 2012 Lecture #02

  12. 0 = 0000 = 0 * 8 + 0 * 4 + 0 * 2 + 0 * 1 1 = 0001 = 0 * 8 + 0 * 4 + 0 * 2 + 1 * 1 2 = 0010 = 0 * 8 + 0 * 4 + 1 * 2 + 0 * 1 3 = 0011 = 0 * 8 + 0 * 4 + 1 * 2 + 1 * 1 ....... 7 = 0111 = 0 * 8 + 1 * 4 + 1 * 2 + 1 * 1 8 = 1000 = 1 * 8 + 0 * 4 + 0 * 2 + 0 * 1 9 = 1001 = 1 * 8 + 0 * 4 + 0 * 2 + 1 * 1 10 (a) = 1010 = 1 * 8 + 0 * 4 + 1 * 2 + 0 * 1 11 (b) = 1011 = 1 * 8 + 0 * 4 + 1 * 2 + 1 * 1 12 (c) = 1100 = 1 * 8 + 1 * 4 + 0 * 2 + 0 * 1 13 (d) = 1101 = 1 * 8 + 1 * 4 + 0 * 2 + 1 * 1 14 (e) = 1110 = 1 * 8 + 1 * 4 + 1 * 2 + 0 * 1 15 (f) = 1111 = 1 * 8 + 1 * 4 + 1 * 2 + 1 * 1 Examples: 09FE (in Hex) == ? (in Binary) == ? (in Decimal) ecs30 winter 2012 Lecture #02

  13. “Memory Box” Each “address-able” box is ONE Byte 1 byte = 8 bits 1 bit is 0 or 1 Binary representation ecs30 winter 2012 Lecture #02

  14. “The story of X” int X; X, &X, *X, ((struct S *) X)->index, ((int *) X)[20], *(((int *) X)+20), ((double *) X)[20], ((struct S *) 0)->index,… ecs30 winter 2012 Lecture #02

  15. Byte versus Double • Each Memory cell is 1 Byte • How about Double? • How will Double map to your hardware memory? ecs30 winter 2012 Lecture #02

  16. Arithmetic Operations in Binary/Bits? +/- 0001 + 0001 = 0010 bit: 0/1 physical memory. byte: 8 bits in Unix, “usually” an integer has 4 bytes, i.e., 32 bits. unsigned 0 ~ 4294967295 (i.e. 2 32 -1) signed -2147483648 ~ 2147483647 (i.e. -(231) ~ (231 - 1)) ecs30 winter 2012 Lecture #02

  17. How do I represent a character? (Internal coding) ASCII (American Standard Code for Information Interchange) use 7 bit to represent a character (might or might not on your keyboard) Example: 'A' 1100001 (in Byte, 0110001) (Appendix A: page 839) Decimal: 65, Hex: 41. Question: How many different characters can we represent? ecs30 winter 2012 Lecture #02

  18. Binary Representation • Integer (int) 4 bytes • Double 8 bytes • Character 1 byte ecs30 winter 2012 Lecture #02

  19. /* an example program for the sizeof operator in C */ #include <stdio.h> main() { printf("The size of an integer is %d.\n", sizeof(int)); printf("The size of a float is %d.\n", sizeof(float)); printf("The size of a double is %d.\n", sizeof(double)); printf("The size of a character is %d.\n", sizeof(char)); } The size of an integer is 4. The size of a float is 4. The size of a double is 8. The size of a character is 1. ecs30 winter 2012 Lecture #02

  20. printf("value = %d, address = %d\n", cats, &cats); ===> value = 3, address = -268438156; **** printf("value = %d, address = %x\n", cats, &cats); ===> value = 3, address = effff574; -268438156 (in decimal) == effff574 (in hex) aa = -268438156; aa = 0xeffff574; ecs30 winter 2012 Lecture #02

  21. ecs30 winter 2012 Lecture #02

  22. { … } • { … } • {… { … {…}…} … {…}…} • int main (void) { … } • float myfunc (int x) { …; return f;} • { <declarations> <statements> } ecs30 winter 2012 Lecture #02

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