QUIZ on Ch.8. What is kit?

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Marshall Miles
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1 QUIZ on Ch.8 What is kit?

2 QUIZ on Ch.8 What is kit? A: A vector of nested structures!

3 QUIZ on Ch.8

4 C crash-course

5 Compilation and Execution of a C Program Run-time

6 Interpreted languages (like MATLAB, Python, etc.) Executing a C program using an interpreter. Interpreted languages are sometimes called scripting languages.

7 Anatomy of a C Program: Hello, world /* File: hello.c Print Hello, world on the screen */ #include <stdio.h> int main() { printf("hello, world\n"); return 0; }

8 How do we declare and initialize variables in C?

9 A longer C Program

13 The primitive data types of MATLAB and C are compatible!

14 Source:

15 C s Boolean Operators are almost the same as MATLAB s ~ or not in MATLAB ~= in MATLAB

16 The for loop in C What does this loop print?

17 QUIZ: for loops Write a for loop to display the numbers from 0 to 10: In MATLAB In C

18 QUIZ: for loops and arrays Write a for loop to store the numbers from 0 to 10 in an array, and then display them: In MATLAB In C

19 Arrays and for loops in C EOL #include <stdio.h> int main() { int a[4][4], i, j; for (i=0; i<4; i++){ for (j=0; j<4; j++){ a[i][j] = i+j; printf("a[%d][%d] = %d\n", i, j, a[i][j]); } } return 0; }

20 The while loop in C What does this loop print?

21 Could we use a for loop instead?

22 while loop and sentinel

23 QUIZ: while loops Write a while loop in C to display the numbers from -5 to 20 (inclusive)

24 Decisions in C: the if statement

25 What does this double loop print? for (i=-100; i<100; i++) for (j= -100; j<100; j++) if (i+j == 42) printf("sum = %d\n", i+j);

26 What does this double loop print? for (i=-100; i<100; i++) for (j= i+1; j<100; j++) if (i+j == 42) printf("sum = %d\n", i+j);

27 As in MATLAB, in C we can have nested ifs

28 Modulus (remainder) operator in C Do you remember how we find the remainder in MATLAB?

29 Solve the Fizz-Buzz problem in C Write a program that prints the numbers from 1 to 100: for multiples of three print "Fizz" instead of the number for multiples of five print "Buzz". for numbers which are multiples of both three and five print "FizzBuzz".

30 Fizz-Buzz one of many solutions EOL2

31 What is this code attempting to do? What is wrong? int x, y; int arr[10][3]; for(x=0; x<3; x++) for(y=0; y<10; y++) arr[x][y] = 42; What will happen when we try to run it?

32 int x, y; int arr[10][3]; for(x=0; x<3; x++) for(y=0; y<10; y++) arr[x][y] = 42; What will happen when we try to run it? Array out of bounds! RUNTIME ERROR!

33 Conclusions Unlike MATLAB, C does not automatically extend arrays when new elements are added. In C, it is the programmer s responsibility to stay within the bounds declared for the array! We have the classical trade-off: MATLAB is safer and more flexible C is more efficient (less memory, faster)

34 Write code to declare and initialize a 10x10 identity matrix

35 Which solution is more efficient? int id[10][10]; int i,j;..... for (i=0; i<10; i++) for (j=0; j<10; j++) if(i==j) id[i][j] = 1; else id[i][j] = 0; int id[10][10] = {0}; int i;..... for (i=0; i<10; i++) id[i][i] = 1;

36 Write code to declare and initialize a 10x10 bidiagonal matrix of ones

37 int id[10][10] = {0}; int i,j;..... for (i=0; i<10; i++) for (j=0; j<10; j++){ if(i==j) id[i][j] = 1; if(i+1==j) id[i][j] = 1; }

38 Write code to declare and initialize a 10x10 tridiagonal matrix of ones

39 Write code to declare and initialize a 10x10 anti-identity matrix

40 Write code to declare and initialize a 10x10 matrix with this pattern of elements. Hint: You have to spot a relationship between the indices i, j of each element, and the value stored in that element.

41 Write code to declare and initialize a 10x10 matrix with this pattern of elements. Hint: You have to spot a relationship between the indices i, j of each element, and the value stored in that element. for (i=0; i<10; i++) for (j=0; j<10; j++) m[i][j] = i+j;

42 Write code to declare and initialize a 10x10 matrix with this pattern of elements. Hint: You have to spot a relationship between the indices i, j of each element, and the value stored in that element.

43 A pointer is defined as a variable which contains the address of another variable (or the address of dynamically allocated memory more on this in Ch.10) Place an asterisk * in front of the variable name: int i, *p; Although not mandatory, it s good programming style to start or end pointer names with p, or even ptr.

44 The Size of Pointer Variables The variable of pointer type is used to hold an address of memory. Its size is implementation-dependent, typically: 4 bytes for 32-bit machines 8 bytes for 64-bit machines It is independent of the variable type that it points to Pointers to char have the same size as pointers to long long int!

45 How can pointers have the same size when the variables they point to have different sizes? This is how we declare pointers short A, *A_ptr; int B, *B_ptr; long long D, *D_ptr; This is how we initialize pointers A_ptr = &A; B_ptr = &B; D_ptr = &D; Image source:

46 How can pointers have the same size when the variables they point to have different sizes? A: The address stored in the pointer is the address of only the first (lowest) Byte of the variable! Image source:

47 Pointer or pointer variable? It s really pointer variable, b/c pointers are also stored in memory, just like regular variables! For simplicity, however, we mostly say just pointer.

48 Where are pointer variables stored? They are also stored in memory, just like regular variables!

49 #include <stdio.h> void main() { char *pc; int *pi; double *pd; } printf("sizeof(char *) = %u\n", sizeof(char*)); printf("sizeof(pc) = %u\n", sizeof(pc)); printf("sizeof(pi) = %u\n", sizeof(pi)); printf("sizeof(pd) = %u\n", sizeof(pd)); Output when the program is executed on a 32-bit machine: sizeof(char *) = 4 sizeof(pc) = 4 sizeof(pi) = 4 sizeof(pd) = 4

50 Pointer Operators & (address operator) To obtain the address of a variable, add the address operator & in front of the variable name. int i = 10; int *iptr; iptr = &i; //iptr gets address of i * (indirection/dereferencing operator) To declare a pointer, place it in front of the identifier. To obtain the value of a variable, place it in front of the pointer s name. *iptr is the value of i Pointers can be used for assignment *iptr = 5; // changes i to 5

51 Pointer Operators The two worlds & is the escalator up * is the escalator down iptr i

52 int myvar; int *ptr; myvar = 12; ptr = &myvar; ptr myvar

53 int i = 10; int *iptr; iptr = &i; Examples //iptr gets address of i iptr i iptr A A A i 42 43

54 #include <stdio.h> void main() { int i, j, *p; i = 10; j = 0; p = &i; /*p is assigned the address of i*/ printf("the value of i is %d\n", i); printf("the value of j is %d\n", j); printf("the address of i is %p\n", &i); printf("the value of p is %p\n", p); printf("the value of *p is %d\n", *p);

55 Output: The value of i is 10 The value of j is 0 The address of i is 00E81E20 The value of p is 00E81E20 The value of *p is 10

56 *p = 20; /*The memory pointed to by p is assigned value20*/ j = *p; /*j is assigned the value pointed to by p*/ } printf("after indirection operations\n"); printf("the value of i is %d\n", i); printf("the value of j is %d\n", j); printf("the address of i is %p\n", &i); printf("the value of p is %p\n", p); printf("the value of *p is %d\n", *p);

57 Output: After indirection operations The value of i is 20 The value of j is 20 The address of i is 00E81E20 The value of p is 00E81E20 The value of *p is 20

58 Example memory map for two integers and one pointer p = &i; If the address of i is 0x00E81E20, the value of p is 0x00E81E20 The program performs the indirection operations: *p = 20; j = *p; BEFORE AFTER

Exercise 3 / Ch.7. Given the following array, write code to initialize all the elements to 0: int ed[100]; Hint: It can be done two different ways!

Exercise 3 / Ch.7. Given the following array, write code to initialize all the elements to 0: int ed[100]; Hint: It can be done two different ways! Exercise 3 / Ch.7 Given the following array, write code to initialize all the elements to 0: int ed[100]; Hint: It can be done two different ways! Exercise 3 / Ch.8 Given the following array, write code