CS1010 AY20/21 S1 Lecture 11

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# Lecture 11

### 2 November 2020

.smaller[
Admin Matters<br>
Unit 28: struct<br>
Unit 29: stdio<br>
]
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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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```C
struct matrix {
  double** array;
  long num_of_rows;
  long num_of_columns;
};
```

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```C
struct list {
  char *array;
  long length;
};
```

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```C
struct module {
  char *code;
  char *title;
  long mc;
};
```
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### Declaring a struct variable

```C
struct module cs1010;
```

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### Initializing a struct variable

.tiny[
```C
struct module cs1010;
cs1010.code = "CS1010";
cs1010.title = "Programming Methodology";
cs1010.mc = 4;
```
]

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### Declaring AND Initializing a struct variable

.tiny[
```C
struct module cs1010 = {
  .code = "CS1010",
  .title = "Programming Methodology",
  .mc = 4
};
```
]
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### Reading and writing members of a `struct`

.tiny[
```C
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

.tiny[
```C
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

.tiny[
```C
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

.tiny[
```C
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)

.tiny[
```C
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)

```C
struct answer {
  long max_n;
  long max_num_steps;
};
```

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.tiny[
```C
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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.tiny[
```C
typedef unsigned char color_t;
  :
void paint(color_t r, color_t g, color_t b) { 
  :
}
```
]

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```C
typedef struct module {
  char *code;
  char *title;
  long mc;
} module;
```

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```C
typedef struct {
  char *code;
  char *title;
  long mc;
} module;
```

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.tiny[
```C
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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```C
printf("%s is a %ld-MC module\n",
   module.code, module.mc);
```

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.tiny[
```
%[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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```C
long width;
long height;
scanf("%ld %ld", &width, &height);
```

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.tiny[
```
%[*][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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.tiny[
Version: 1.0

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