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Lecture 11

2 November 2020

Admin Matters
Unit 28: struct
Unit 29: stdio

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  • PE2 this Saturday
  • Arrangement for final
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Tutorial/Lab 10

  • Assignment 8
  • PE2 from 18/19
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Compound Data Type

  • Array: multiple values of the same data type
  • Structure: multiple values of different data types
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Some things belong together

  • 1D array and its length
  • 2D array, its width, and its height
  • x and y position in a maze
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Defining a struct

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struct matrix {
  double** array;
  long num_of_rows;
  long num_of_columns;
};
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struct list {
  char *array;
  long length;
};
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struct module {
  char *code;
  char *title;
  long mc;
};
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Declaring a struct variable

struct module cs1010;
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Initializing a struct variable

struct module cs1010;
cs1010.code = "CS1010";
cs1010.title = "Programming Methodology";
cs1010.mc = 4;
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Declaring AND Initializing a struct variable

struct module cs1010 = {
  .code = "CS1010",
  .title = "Programming Methodology",
  .mc = 4
};
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Reading and writing members of a struct

cs1010.mc = hours_spent_per_week/2.5;
cs1010_println_long(cs1010.mc);
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struct as pass-by-value parameters to a function

void update_mc(struct module cs1010, long weekly_hours_spent) {
  cs1010.mc = weekly_hours_spent/2.5;
}
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struct as pass-by-reference parameters to a function

void update_mc(struct module *cs1010, long weekly_hours_spent) {
  (*cs1010).mc = weekly_hours_spent/2.5;
}
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struct as pass-by-reference parameters to a function

void update_mc(struct module *cs1010, long weekly_hours_spent) {
  cs1010->mc = weekly_hours_spent/2.5;
}
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How to pass multiple values back to caller (Method 1)

void find_max_steps(long n, long *max_n, long *max_num_steps) {
  *max_num_steps = 0;
  *max_n = 1;
  for (long i = 1; i <= n; i += 1) {
    long num_of_steps = count_num_of_steps(i);
    if (num_of_steps >= *max_num_steps) {
      *max_n = i;
      *max_num_steps = num_of_steps;
    }
  }
}
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How to pass multiple values back to caller (Method 2)

struct answer {
  long max_n;
  long max_num_steps;
};
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struct answer find_max_steps(long n) {
  struct answer ans = {
    .max_n = 1,
    .max_num_steps = 0
  };
  for (long i = 1; i <= n; i += 1) {
    long num_of_steps = count_num_of_steps(i);
    if (num_of_steps >= ans.max_num_steps) {
      ans.max_n = i;
      ans.max_num_steps = num_of_steps;
    }
  }
  return ans;
}
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Defining Your Own Type

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typedef unsigned char color_t;
  :
void paint(color_t r, color_t g, color_t b) { 
  :
}
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typedef struct module {
  char *code;
  char *title;
  long mc;
} module;
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typedef struct {
  char *code;
  char *title;
  long mc;
} module;
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void update_mc(module cs1010, long weekly_hours_spent) {
  cs1010.mc = weekly_hours_spent/2.5;
}
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Reading and Printing without libcs1010

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printf and scanf

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printf("%s is a %ld-MC module\n",
   module.code, module.mc);
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%[flags][field_width][.precision][length_modifier]specifier
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  • printf behaves differently from functions that you have been writing.

  • It takes in different number of arguments of different type.

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long width;
long height;
scanf("%ld %ld", &width, &height);
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%[*][field_width][length_modifier]specifier
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  • space in between the format specifier matches zero or more white spaces (space, tab, newline)

  • Scanning stops when an input character does not match such a format character or when an input conversion fails

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Version: 1.0

Last Updated: Sun Nov 1 11:59:04 +08 2020

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  • PE2 this Saturday
  • Arrangement for final
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