String Class in C++

There is no native “string” data type in C++ but its <string> library class provides a string object that emulates a string data type. To make this available to a program, the library must be added with an #include <string> directive at the start of the program.

#include<iostream>
#include<string.h>using namespace std;
int main()
{
    char str[50];
    int len;
    cout << "Enter an array or string : ":
    gets(str);
    len = strlen(str);
    cout << "Length of the string is : " << len;
    return 0;
}

Like the <iostream> class library, the <string> library is part of the std namespace that is used by the C++ standard library classes. That means that a string object can be referred to as std::string, or more simply as string when using namespace std; again the directive must be at the start of the program.

Initializing Strings

A string “variable” can be declared in the same way as other variables. The declaration may optionally initialized the variable using the = assignment operator, or it may be initialized later in the program. Additionally a string variable may be initialized by including a text string between parentheses after the variable name.

Text strings in C++ must always be enclosed with double quotes(“”).
Single quotes (‘’) are only used for character values of the char data type.

Any numeric values that are assigned to a string variable, are no longer a numeric data type, so attempting to add string values of “4” and “5” with the addition operator(+) would add up to “45” instead of 9.

Converting Strings to other Data Types

Arithmetic cannot be performed on numeric values assigned to string variables until they are converted to a numeric data type. Luckily, there is a C++ <sstream> library provides a “stringstream” object that acts as an intermediary to convert strings to other data types.

Other features of a string variable can be revealed by calling its size(), capacity(), and empty() functions. Written below is short summary of other features.

• a string variable can be emptied by assigning it an empty string (=“”) or by calling its clear() function.
• Multiple string values can be concatenated by the + operator
• A string can be can be appended to another string by the += operator or by calling its append() function.
• A string can be compared to another string by the == operator or by calling its append() function.
• A string can be assigned to a string variable using the = operator or by calling its assign() function.
• The swap() function swaps the values of two string variables.
• Substrings of a string can be sought with the find() function, or specialized functions such as find_first_of(), and a character retrieved from a specified index position by the at() function.

Next we will be focusing more on control structure of the flow such as while loops, do-while loops, and for loops in addition to using the switch case for complex conditional tests.