LECTURE 38:TYPEDEFS

CSC 107 – Programming For Science

Today’s Goal

Discover best uses of structures in a program Using typedef to make meaningful names

Creating A struct

Declare struct outside of any function After #includes where normally find

declarations Within struct, must declare 1 or more

fields Name & data type required for each field Fields can be listed in any order Any type can be used for fields, even struct types struct student { double gpa; char name[40]; // Arrays are okay int *year; // Pointers fine, also};

Using structs

Type of the variable is specific struct Fields are like variable just as array

entries are Requires having actual variable to access Each field is set & used independent of

others Code can access field as

variableName.fieldName No link between fields, even if from

same struct

Assigning structs

Like all variables, can assign structs Identical struct type needed for source &

target Works like assigning fields in source to

fields in target Primitive values are copied like primitive

variables With assignment, arrays & pointers alias

same value Fields just like variables of the same

type Can be used just like any variable of that

type Need struct to get access to the field

initially

Pointers to struct

Like all other types, can have pointer to struct Assign using & to get address of struct

variable Can also dynamically allocate array using new

2 ways to access fields with struct pointers Follow pointer to struct & use the .

operator(*pointerToStruct).fieldName

Use pointer operator, ->, to access field directlypointerToStruct->fieldName

typedefs For Simplicity

Make synonyms for types using a typedef:typedef original type new_name;

Simplify & clarify code by making types meaningful

Synonym only for coder; computer ignores difference

Really creates shorthand; does NOT make new type

typedef long BIG_INTEGER;typedef unsigned long bob;typedef char * CSTRING;typedef struct energy ENERGY;

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Will It Compile?

typedef int MIDDLE;typedef char* CSTRING;typedef struct energy ENERGY;MIDDLE i = 5;CSTRING str = “Bob”;struct energy ball;ENERGY *nerf = &ball;int j = i;strcpy(str, “Yo, whatup dog”);nerf = new struct energy[100];i++;str = new CSTRING[23];nerf = new ENERGY[12];nerf[2] = ball;str = new char[42];

Your Turn

Get into your groups and try this assignment

For Next Lecture

Spend 1 last day on structs on Monday Write better solution to well-known problem Understand why structs used in real-world

problems Before moving on in class, solidify students

knowledge Angel has Weekly Assignment #14 for

Tuesday

Last programming assignment due in 1 week