1 review of chapter 10: string and pointers. 2 outline string: representation of a string: \0 ...

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Review of Chapter 10:String and Pointers

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Outline

String: Representation of a string: \0 Using scanf to read in string Initilization of strings

String-Handling Functions in the Standard Library

Passing Arguments to main() using an array of strings

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String

A string is a one-dimensional array of type char.

char w[100]; character value \0 is used to terminate a string

strings have a variable length delimited by the null character \0 but with a maximum length determined by the size of the character array

The size of the string must include the storage needed for the null character \0.

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The End-of-String Sentinel \0

Example:

#include <stdio.h>int main(void){ char w[100]; w[0]='A'; w[1]='B'; w[2]='C'; w[3]='\0'; printf("%s\n", w);}

% a.outABC

#include <stdio.h>int main(void){ char w[100]; w[0]='A'; w[1]='B'; w[2]='C'; w[3]='\0'; w[4]=‘D'; printf("%s\n", w);}% a.out

ABC

the null character value \0 is used to terminate a string

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Using scanf to reading string

Using scanf to read in a string scanf(“%s”, w);

read in non-white space characters o positions the input stream to an initial non-

white space charactero read in non-white space characterso The process stops when a white space

character or EOF is encountered.

a null character is placed in memory to end the string.

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Using scanf to reading string

#include <stdio.h>int main(void){ char w[10]; printf("Enter strings\n", w); scanf("%s", w); printf("%s\n", w);}% a.outEnter stringsHelloHello

% a.outEnter stringsHello WorldHello

scanf(”%s”,w);

read in non-white space characters

positions the input stream to an initial non-white space characterread in non-white space charactersThe process stops when a white space character or EOF is encountered.

a null character is placed in memory to end the string.

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Initialization of Strings

Initialization of Strings Example: initialize a string variable as “abc”

char s[] = {‘a’, ‘b’, ‘c’, ‘\0’};char s[]=“abc”;

#include <stdio.h>int main(void){ char w[]="abc"; printf("%d\n", sizeof(w));}

% a.out4

The size of the string must include the storage needed for the null character \0.

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Initialization of Strings

A pointer to char can also be initialized with a constant string.

A string constant is stored in memory by the compiler.

the pointer is assigned the address of the constant string in memory.

Example: char p* = “abc”;#include <stdio.h>int main(void){ char *p="abc"; printf("%s\n",p);}

% a.outabc

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Initialization of Strings

Difference between initializing an array with a constant string

the array contains the individual characters followed by the null character

initializing a pointer with a constant stringA string constant is stored in memory by

the compiler.the pointer is assigned the address of the

constant string in memory.

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String-Handling Functions in the Standard Library

String-handling functions: Function prototypes are provided by string.h

#include <string.h> Functions:

Concatenate two strings: strcat (s1, s2);Compare two strings: int strcmp (s1, s2);Copy s2 to s1: strcpy (s1, s2);Length of a string: strlen (s);

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Outline

String: Representation of a string: \0 Using scanf to read in string Initilization of strings

String-Handling Functions in the Standard Library

Passing Arguments to main() using an array of strings

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Passing Arguments to main()

Unix Commands, take arguments %pico q1.c %gcc q12.c prime.c %gcc –lm q12.c prime.c

In our project, write code, compile, execute a.out %a.out Can we pass arguments to our program? Can we pass arguments to the main()

function?

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Passing Arguments to main()

How main() communicates with the operating system? int main(void) int main( int argc, char *argv[])

argc: the number of the command line arguments

argv: an array of strings

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Passing Arguments to main()

#include <stdio.h>int main(int argc, char *argv[]){ int i; printf("%d \n", argc); for (i=0; i < argc; ++ i) printf("%s\n", argv[i]);}

%a.out Hello World3a.outHelloWorld

argc: the number of the command line argumentsargv: an array of strings

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Summary

String: Representing a string using an array of characters \0 is used to terminated a string

strings have a variable length delimited by the null character \0 but with a maximum length determined by the size of the character array

initialization of strings

String-Handling Functions in the Standard Library

Passing Arguments to main() argc: number of arguments argv: an array of strings

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End of Chapter 10: String and PointersRead 10.1 – 10.10

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Chapter 12 Structures and ADTs

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Introduction

Programming Questions: How to represent a date?

Three components are required:o day, month, year

Three variables can be used to represent a date.

o int day, month, year; /* date */

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Introduction

Programming Questions: How to represent a student record?

components: o last_name, first_name;o UINo scores of six assignments;o scores of three midterms and final;

Six variables are required to represent a student record.

o char[20] last_name;o char[20] first_name;o int UIN;o int assignment[6], midterm[3], final;

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Introductionrepresent a student record. char[20] last_name; char[20] first_name; int UIN; int assignment[6], midterm[3],

final;

represent a date.int day, month, year;

Can we represent a collection of components of possibly different types by a single variable?

A derived date type — structureStructure is a means of aggregating

a collection of data items of possibly different types.

components are individually named.These components are called

members.

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Chapter 12: Structures and ADTs

Outline Declaring Structures Accessing a Member in a structure variable Initialization of Structures

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Declaring Structures

How to declare a structure data type? Example: a structure type to represent a

date: Components: day, month, yearstruct date_str{

int day;int month;int year;

};

This declaration creates the derived date type struct date_str.

members of the structure

structure tag name

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Declaring Structures

How to declare variables of a structure type? Declare variables in declaration of a structure type

struct date_str{int day;int month;int year;

} date1, date2; Declare variables “struct str_name variable_list;”

struct date_str{int day;int month;int year;

}; struct date_str date3, date4;

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#include <stdio.h>

int main(void){ struct date_str{ int day; int month; int year; } date1, date2;

printf("Input data in format DD/MM/YYYY:"); scanf("%d/%d/%d", &date1.day, &date1.month, &date1.year);

printf("Input data in format DD/MM/YYYY:"); scanf("%d/%d/%d", &date2.day, &date2.month, &date2.year);}

struct date_str{ int day; int month; int year; }; struct date_str date1; struct date_str date2;

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#include <stdio.h>int main(void){ struct student_str{ char last_name[15]; char first_name[15]; int UIN; int assign[6]; int midterm[3]; int final; } students[110];

int i; printf("Input last name, first name and UIN for each students:\n"); for (i=0; i< 110; i++){ scanf("%s", students[i].last_name); scanf("%s", students[i].first_name); scanf("%d", &students[i].UIN); }}

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Declaring Structures

Summary: Declare a structure type Declare variables of a structure type The declaration of a structure type creates a

derived date type.No storage is allocated upon this

declarationStorage is allocated when variables are

declared of a structure type.

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Chapter 12: Structures and ADTs

Outline Declaring Structures Accessing a Member in a structure variable Initialization of Structures

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Access a member

How to access a member? member operator “.”

structure_variable.member_name Example:

struct date_str{int day;int month;int year;

} date1, date2;date1.year = 2000; data2.year= 2005;date1.day = date2.day = 10;date1.month = date2.month = 11;

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#include <stdio.h>

int main(void){ struct date_str{ int day; int month; int year; } date1, date2;

printf("Input data in format DD/MM/YYYY:"); scanf("%d/%d/%d", &date1.day, &date1.month, &date1.year);

printf("Input data in format DD/MM/YYYY:"); scanf("%d/%d/%d", &date2.day, &date2.month, &date2.year);}

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#include <stdio.h>int main(void){ struct student_str{ char last_name[15]; char first_name[15]; int UIN; int assign[6]; int midterm[3]; int final; } students[110];

int i; printf("Input last name, first name and UIN for each students:\n"); for (i=0; i< 110; i++){ scanf("%s", students[i].last_name); scanf("%s", students[i].first_name); scanf("%d", &students[i].UIN); }}

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Accessing a Member

Question: Given the following declaration:

struct date_str{ int day; int month; int year; } date1;struct date_str *pDate = &date1;

How to access the members of the variable to which pDate points?

(*pDate).day

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Accessing a Member

How to access a member? structure pointer operator ->

access the members of a structure via a pointer.

pointer_to_structure -> member_name (*pointer_to_structure).member_name

Example: struct date_str *pDate = &date1;

(*pDate).day pDate->day

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#include <stdio.h>struct date_str{ int day; int month; int year;};void getDate(struct date_str *pDate);void printDate(struct date_str *pDate);

#include "date.h"int main(void){ struct date_str date1, date2; getDate(&date1); getDate(&date2); printDate(&date1); printDate(&date2);}

date.h

#include "date.h“

void getDate(struct date_str *pDate){ printf("Input a date in DD/MM/YYYY:"); scanf("%d/%d/%d", &(pDate->day), &(pDate->month), &(pDate->year));}void printDate(struct date_str *pDate){ printf("The input date is: %d/%d/%d\n", pDate->day, pDate->month, pDate->year);}

date.c gcc date.c main.c

main.c

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Notes The member name must be unique within

the specified structurestruct name_str{

char[15] last_name;char[15] first_name;

};struct name_str{

char[15] name;char[15] name;

}; X

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Notes Can we have two members having the same

name in different structures?Since the member must always be

accessed through a unique structure variable identifier, there is no confusion

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Accessing a Member

Summary member operator “.”

structure_variable.member_name structure pointer operator “ -> ”

access the members of a structure via a pointer.

pointer_to_structure -> member_name (*pointer_to_structure).member_name

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Chapter 12: Structures and ADTs

Outline Declaring Structures Accessing a Member in a structure variable Initialization of Structures

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Initialization of Structures

Initialization A structure variable can be followed by

an equal sign = and a list of constants contained within braces

Example:struct date_str{ int day; int month; int year;};struct date_str date={12, 12, 2000};

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Initialization of Structures

Initialization If there are not enough values, the remaining

members are assigned the value zero. Example:

struct student_str{ char last_name[15]; char first_name[15]; int UIN; int assign[6]; int midterm[3]; int final; }

strcut student_str s1={“Bush”, “Jenny”, 80002211};

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Chapter 12: Structures and ADTs

Summary Declaring Structures Accessing a Member in a structure variable

member operator “.”:o structure_variable.member_name

structure pointer operator “ -> ” :o pointer_to_structure -> member_name

Initialization of StructuresA structure variable can be followed by

o an equal sign = and o a list of constants contained within braceso If there are not enough values, the remaining

members are assigned the value zero.

Read Chapter 12.1 – 12. 6