Transcript Programmer-defined functions

Arrays Review
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What is an aggregate construct?
What is an array?
What is name of the array? What is index?
What is indexed variable? Element of the array? Scalar variable?
What is array size?
What is array’s base type?
How is array declared?
What number do indexes start from?
What is out-of-range error? Is it a syntax error or a bug?
Can arrays be passed as arguments to functions? If yes by value or by
reference? If yes, how does size of array passed?
What does const mean in the following declaration?
void myfunc(const int []);
how do you initialize arrays at declaration?
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Strings
Declaring Strings
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strings are specific constructs that are geared towards processing
sequences of characters
before using, include string header: #include <string>
don’t use string.h
as well as using std::string;
string declaration:
string mystr;
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value assignment at declaration:
string mystr(”Hello”);
string mystr2=”Hello”;
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assignments from other types are not permitted:
string error1 = ’c’; // error
string error2 = 22; // error
can assign a character with assignment operator:
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mystr=’n’;
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String I/O
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String can be output as any other type:
string s=”hello world”;
cout << s << endl;
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two ways to input strings:
 using extraction operator - strips white space and assigns the first token
(word) to the string:
cin >> s;
hello world\n input assigns only hello to s
 using getline function - assigns all characters to string up to newline
(not included, \n is discarded):
getline(cin, s);
hello world\n input assigns hello world to s
 to successfully mix getline and extraction, may need
cin.peek() – returns next character without removing
cin.get() – returns a single next character
cin.unget() – puts previously returned character back into cin
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String Assignment and
Concatenation
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use assignment operator as with other types:
string s1, s2, s3;
s1=”C++”;
s2=”fun”;
plus “+” is used for string concatenation: s3=s1 + ” is ” + s2;
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at least one operand has to be string variable!
compound concatenation allowed:
s1 += ” language”;
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characters can be concatenated with strings:
s2 = s1 + ’o’;
s2+=’o’;
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no other types can be assigned to strings or concatenated with strings:
s2= 42.54;
// error
s2=”Catch” + 22; // error
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Comparing Strings
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comparison operators (>, <, >=, <=, ==, !=) are applicable to strings
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strings are compared lexicographically:
string s1=”accept”, s2=”access”, s3=”acceptance”;
s1 is less than s2 and s1 is less than s3
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the following rules hold:
 letters in the alphabet are in the increasing order
 longer word (with the same characters) is greater than shorter word
comparison to literal string constants and named constants is also legal:
const string myname=”John Doe”;
string hername=”Jane Doe”;
if ((myname==hername)||(myname==”Jake Doe”))
cout << ”found him\n”;
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String Functions
String Characteristics
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a number of standard functions are defined for strings. Usual syntax:
string_name.function_name(arguments)
useful functions return string paremeters:
 size() - current string size (number of characters currently
stored in string
 length()- same as size()
 max_size() - maximum number of characters in string allowed
on this computer
 empty() - true if string is empty
example:
string s=”Hello”;
cout << s.size();
outputs 5
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Accessing Elements of Strings
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similar to arrays a character in a string can be accessed and assigned
to using its index (start from 0)
cout << str[3];
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it is an error to access an element beyond the size of the string:
string s=”Hello”; // size is 5
cout << s[6];
// error
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the type of the element of the string is character, assigning integers,
strings and other types are not allowed
s[3] = ”hi”;
// error
s[3] = 22;
// error
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Substrings, Searching
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substr - function that returns a stubstring of a string:
substr(start, numb) - start - index of the first character,
numb - number of characters
string s=”Hello”; // size is 5
cout << s.substr(3,2); // outputs ”lo”
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find family of functions return position of substring found, if not found
return global constant string::npos defined in string header
 find(substring) - returns the position of the first character of
substring in the string
 rfind(substring) - same as find, search in reverse
 find_first_of(substring) - find first occurrence of any
character of substring in the string
 find_last_of(substring) - find last occurrence of any
character of substr in the string
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all functions work with individual characters as well:
cout << s.find(’l’);
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Inserting, Replacing
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insert(start, substring)- inserts substring starting from
position start
string s=”place”;
cout << s.insert(1, ”a”); //produces ”palace”
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variant insert(start, number, character) – inserts number of
character starting from position start
string s=”place”;
cout << s.insert(4, 2, ’X’); //produces ”placXXe”
note it is a character not a string
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replace (start, number, substring)- replaces number of
characters starting from start with substring the number of
characters replaced need not be the same
string s=”Hello”;
s.replace(1,4, ”i, there”); //produces ”Hi, there”
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Appending, Erasing
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append(string2)- appends string2 to the end of the string
string s=”Hello”;
cout << s.append(”, World!”);
cout << s; // outputs ”Hello, World!”
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erase(start, number)- removes number of characters starting
from start
string s=”Hello”;
s.erase(1,2);
cout << s; // outputs ”Hlo”
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Passing Strings as Parameters
Returning Strings
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strings can be passed as parameters:
 by value:
void myfunc(string s);
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by reference:
void myfunc(string &s);
if string is not modified by function use const type modifier:
void myfunc(const string &s);
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strings (unlike arrays) can be returned:
 string myfunc(int, int);
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note, that passing strings by value and returning strings is less
efficient than passing them by reference
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