In general or more specifically in competitive programming there are many instances where we need to convert a number to a string or string to a number. But lack of knowledge of certain essential tools bind us to do so. Some methods to achieve this task are mentioned in this article.
Converting string to number
Method 1 : Using stringstream class or sscanf()
Method 2 : String conversion using stoi() or atoi()
Both these methods have been discussed in detail in the this article.
Method 3 : Using boost lexical cast
Boost library offers an inbuild function “lexical_cast(“string”)”, which directly converts a string to number. It returns an exception “bad_lexical_cast” in case of invalid input.
//C++ code to demonstrate working of lexical_cast() #include<iostream> #include <boost/lexical_cast.hpp>// for lexical_cast() #include <string> // for string using namespace std; int main() { string str = "5"; string str1 = "6.5"; // Initializing f_value with casted float // f_value is 6.5 float f_value = boost::lexical_cast<float>(str1); // Initializing i_value with casted int // i_value is 5 int i_value = boost::lexical_cast<int>(str); //Displaying casted values cout << "The float value after casting is : "; cout << f_value <<endl; cout << "The int value after casting is : "; cout << i_value <<endl; return 0; } |
Output:
The float value after casting is : 6.5 The int value after casting is : 5
Converting number to string
Method 1 : Using string streams
In this method, string stream declares a stream object which first inserts a number, as a stream into object and then uses “str()” to follow internal conversion of number to string.
// C++ code to demonstrate string stream method // to convert number to string. #include<iostream> #include <sstream> // for string streams #include <string> // for string using namespace std; int main() { int num = 2016; // declaring output string stream ostringstream str1; // Sending a number as a stream into output // string str1 << num; // the str() coverts number into string string geek = str1.str(); // Displaying the string cout << "The newly formed string from number is : "; cout << geek << endl; return 0; } |
Output:
The newly formed string from number is : 2016
Method 2 : Using to_string()
This function accepts a number(can be any data type) and returns the number in the desired string.
Implementation:
// C++ code to demonstrate "to_string()" method // to convert number to string. #include<iostream> #include<string> // for string and to_string() using namespace std; int main() { // Declaring integer int i_val = 20; // Declaring float float f_val = 30.50; // Conversion of int into string using // to_string() string stri = to_string(i_val); // Conversion of float into string using // to_string() string strf = to_string(f_val); // Displaying the converted strings cout << "The integer in string is : "; cout << stri << endl; cout << "The float in string is : "; cout << strf << endl; return 0; } |
Output:
The integer in string is : 20 The float in string is : 30.500000
Method 3 : Using boost lexical cast
Similar to string conversion, the ” lexical_cast() ” function remains the same, but this time argument list modifies to “lexical_cast(numeric_var).
// C++ code to demonstrate "lexical_cast()" method // to convert number to string. #include <boost/lexical_cast.hpp> // for lexical_cast() #include <string> // for string using namespace std; int main() { // Declaring float float f_val = 10.5; // Declaring int int i_val = 17; // lexical_cast() converts a float into string string strf = boost::lexical_cast<string>(f_val); // lexical_cast() converts a int into string string stri = boost::lexical_cast<string>(i_val); // Displaying string converted numbers cout << "The float value in string is : "; cout << strf << endl; cout << "The int value in string is : "; cout << stri << endl; return 0; } |
Output:
The float value in string is : 10.5 The int value in string is : 17
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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