Lecture 8 b Strings BJ Furman 15 OCT

Lecture 8 b: Strings BJ Furman 15 OCT 2012

Overview n Strings ¨ ¨ ¨ What is a string? How do you declare and initialize an string? How can you use a string? String Examples n String Practice n

Learning Objectives n Explain what a string is ¨ Explain the connection between arrays and strings n Declare and initialize a string n Use a string in a program

What is a String? n Last time we looked at arrays ¨ data structures that contain a collection of data objects of the same data type n. A string is an array of characters terminated by the NUL character ¨ ¨ Data type is array of characters The NUL character is a character with a numeric value of zero n n String ¨ constant (or string literal) Any series of characters enclosed in double quotes n n String ¨ ¨ In C, it is represented by the escape sequence, (NUL) Ex. "Hello world" example program stores a string constant stores individual elements n n note: character constants note: terminate with '‘ to make the character array a string /* strings 1. c */ What is an array? #include <stdio. h> int main() { int i; char str 1[] = "Hello world"; char str 2[5]; str 2[0]='M'; str 2[1]='E'; str 2[2]='3'; str 2[3]='0'; str 2[4]=''; printf("str 1==%sn", str 1); for(i=0; i<5; i++) { printf("str 2[%d]==%cn", i, str 2[i]); } return 0; } strings 1. c

Initializing String Variables n Declare as an array of type char ¨ ¨ Can initialize implicitly or explicitly (using a string constant or using individual characters and a terminating NUL character) n If explicit, make sure that: /* strings 1. c */ #include <stdio. h> int main() { int i; char str 1[] = "Hello world"; char str 3[12] = "Hello world"; char str 2[5]; str 2[0]='M'; str 2[1]='E'; str 2[2]='3'; str 2[3]='0'; str 2[4]=''; printf("str 1==%sn", str 1); for(i=0; i<5; i++) { printf("str 2[%d]==%cn", i, str 2[i]); } return 0; }

American Standard Code for Information Interchange (ASCII) Table

Printing Strings to stdout n n Can print an entire string using printf and %s format specification Can print individual elements of a string by indexing and using %c format specification /* strings 1. c */ #include <stdio. h> int main() { int i; char str 1[] = "Hello world"; char str 3[12] = "Hello world"; char str 2[5]; str 2[0]='M'; str 2[1]='E'; str 2[2]='3'; str 2[3]='0'; str 2[4]=''; printf("str 1==%sn", str 1); for(i=0; i<5; i++) { printf("str 2[%d]==%cn", i, str 2[i]); } return 0; }

Strings - Practice 1 n Declare: ¨ n A string variable named me 30, and initialize it to hold the string, "ME 30 rocks!" Determine ¨ ¨ The minimum number of character array elements needed to store the string length of the string What is stored in me 30[2]? What is stored in me 30[12]?

Strings - Practice 1 - solution n Declare: ¨ char me 30[]="ME 30 rocks!" ¨ 13 Try sizeof(me 30)/sizeof(char) n Or strlen(me 30)+ 1 n ¨ ¨ me 30[2]== space What is stored in me 30[12]== ‘’

Manipulating Strings in C n No native support for strings in C ¨ n #include <string. h> See: http: //www. cppreference. com/wiki/c/string/start ¨ ME 30 website | Programming Resources | C Programming Language Related | Language References | The Standard C Library (from cppreference. com)

Copying and Concatenating Strings n to copy str 2 to str 1 (order resembles assignment): ¨ strcpy(str 1, str 2); n n str 1 = str 2; /* Will NOT work!! */ to add (concatenate) str 2 to the end of str 1: ¨ strcat(str 1, str 2); n returns the value of str 1 with str 2 added to the end Note: it clobbers the /0 at the end of str 1 ¨ Make sure that str 1 has room for str 2 ¨ n Example: strings 2_copy_concat. c

Finding the Length of a String n Use strlen(string) ¨ n returns length of the string Example: strings 3_copy_concat_length. c

Review

References Standard C String and Character Library, http: //www. cppreference. com/wiki/c/string/ start. Visited 22 MAR 2010. n http: //www. asciitable. com/. Visited 03 OCT 2009. n