Week 3 Lecture 1

Procedures and functions

Help Sessions

https://discourse02.cse.unsw.edu.au/25T2/COMP1511/t/help-sessions-starting-this-week-week-3/134

Week 2 recap

Nested loops

Simply, a while loop within a while loop
Useful for 2-dimensional data (like grids)

   col
row 1 2 3 4 5
    1 2 3 4 5
    1 2 3 4 5
    1 2 3 4 5
    1 2 3 4 5

#include <stdio.h>

#define ROWS 5
#define COLUMNS 5

int main() {
    int i = 0;

    while (i < ROWS) {
        int j = 1;
        while (j <= COLUMNS) {
            printf("%d ", j);
            j++;
        }
        printf("\n");
        i++;
    }

    return 0;
}

structs

A defined structure of data types, each accessible
Memory is set aside for each field in each struct
Useful for assigning a variable to an organised record of data

struct pokemon {
    int hp;
    double weight
};

enums

A possible set of values
Useful for creating labels in your code

enum elemental_type { FIRE, WATER, GRASS, DARK };

Week 3 Lecture 1

Procedures and functions

Functions

So far, you have used functions in your code
Examples include printf, scanf, main...
What actually are these?

Functions

Functions are reusable blocks of code
Functions (may) have:
- input (parameters)
- actions (side effects)
- output (results)

Functions

We call functions to execute their body, providing any input necessary
We can access the result of the function
We can call a function from anywhere in our programs

Function definition example

int add(int x, int y) {
    return x + y;
}

int ... -> return type (what type should the result be
add -> the name of the function
(int x, int y) -> the parameters, what sequence and type of input must be passed in?
return -> evaluate the expression and return the result

Function call syntax

add(2, 5);

After we define functions, we want to use them
The () after the name of the function means call
We must pass in the correct sequence of arguments of the correct type (int add required two integers).

Function calling

We can pass in variables too

// A simple function which accepts two integers (x, y),
// and returns the result (int) of adding them.
int add(int x, int y) {
    return x + y;
}

int main(void) {
    int year_born = 1994;
    int age = 29;
    
    add(year_born, age);
}

Retrieving the result of a function

// A simple function which accepts two integers (x, y),
// and returns the result (int) of adding them.
int add(int x, int y) {
    return x + y;
}

int main(void) {
    int year_born = 1994;
    int age = 29;
    
    int current_year = add(year_born, age);
}

DEMO

Functions terminology

return type -> the type of data returned by the function
result -> the actual value returned from a function call
parameters -> the type, and sequence of data to be passed into a function (the placeholders)
argument -> the actual value passed into a function's parameters when called
return -> the keyword used to end a function and return the result following

Procedures

not a real thing in C, but a useful way to think about some types and roles of functions

Procedures

Not all functions have to return a result
We call these void functions, or procedures
Procedures do something, but don't have a result
procedures (usually) have a side-effect

procedures

shut_door

side effect?

result?

functions

check_door_shut

side effect?

result?

procedure syntax

void check_door_shut() {

}

This is a function which returns nothing (void)
We could call this a procedure

Order matters

Functions/procedures have to be defined before they care called

we can get around this with function prototypes
Place int add(int x, int y); at the top of your file to define the int add function for later use

When writing functions in your program, think:

What must I give this function so it can do its job?
What should it be named?
What should it return back to me to achieve its goal? (If anything).
Am I re-writing code that could be turned into a reusable function?

Functions are very important

They change how we think about code
When you come across useful, repeatable functionality - make it a function

0, 1, ∞

Lecture Feedback