Dec 12, 2019  A C program might contain more than one compilation unit. To declare an entity that is defined in a separate compilation unit, use the extern keyword. The information in the declaration is sufficient for the compiler, but if the definition of the entity cannot be found in the linking step, then the linker will raise an error. Mar 11, 2019  C STL stoi function stoi stands for string to integer, it is a standard library function in C STL, it is used to convert a given string in various formats (like binary, octal, hex or a simple number in string formatted) into an integer. To declare a variable in C, we write the data-type that we want the variable to contain, followed by the variable's name, followed by a semicolon. One of the primitive data types is an int eger, as we glossed over in the previous tutorial when talking about the 'main' function. How to Convert String to Int C In C, data types are used to distinguish particular types of data. For example, strings are used to store text, booleans are used to store true/false values, and integers are used to store whole numbers (numbers that do not have a decimal point). When writing code in C.

• C++ Basics

• C++ Object Oriented

• C++ Advanced

• C++ Useful Resources

• Selected Reading

C++ provides following two types of string representations −

• The C-style character string.
• The string class type introduced with Standard C++.

The C-Style Character String

The C-style character string originated within the C language and continues to be supported within C++. This string is actually a one-dimensional array of characters which is terminated by a null character '0'. Thus a null-terminated string contains the characters that comprise the string followed by a null.

The following declaration and initialization create a string consisting of the word 'Hello'. To hold the null character at the end of the array, the size of the character array containing the string is one more than the number of characters in the word 'Hello.'

If you follow the rule of array initialization, then you can write the above statement as follows −

Following is the memory presentation of above defined string in C/C++ −

Actually, you do not place the null character at the end of a string constant. The C++ compiler automatically places the '0' at the end of the string when it initializes the array. Let us try to print above-mentioned string −

When the above code is compiled and executed, it produces the following result −

C++ supports a wide range of functions that manipulate null-terminated strings −

Following example makes use of few of the above-mentioned functions −

When the above code is compiled and executed, it produces result something as follows −

The String Class in C++

The standard C++ library provides a string class type that supports all the operations mentioned above, additionally much more functionality. Let us check the following example −

When the above code is compiled and executed, it produces result something as follows −

The usual way of declaring an array is to simply line up the type name, followed by a variable name, followed by a size in brackets, as in this line of code:

This code declares an array of 10 integers. The first element gets index 0, and the final element gets index 9. Always remember that in C++ arrays start at 0, and the highest index is one less than the size. (Remember, index refers to the position within the array, and size refers to the number of elements in the array.)

A common question that the usual programming student asks is, “Can I just declare an array without specifying a size?” The line would look like this:

In certain situations, you can declare an array without putting a number in the brackets. For example, you can initialize an array without specifying the number of elements:

The compiler is smart enough to count how many elements you put inside the braces, and then the compiler makes that count the array size.

Specifying the array size helps decrease your chances of having bugs, bugs, everywhere bugs. Plus, it has the added benefit that, in the actual declaration, if the number in brackets does not match the number of elements inside braces, the compiler issues an error, at least if the number is smaller anyway. The following

yields this compiler error:

But if the number in brackets is greater than the number of elements, as in the following code, you will not get an error. So be careful!

You also can skip specifying the array size when you pass an array into a function, like this:

This technique is particularly powerful because the AddUp function can work for any size array. You can call the function like this:

But this way to do it is kind of annoying because you have to specify the size each time you call in to the function. However, you can get around this problem. Look at this line of code:

With the array, the sizeof operator tells you how many bytes it uses. But the size of the array is usually the number of elements, not the number of bytes. So you divide the result of sizeof by 4 (the size of each element).

C++ Stoi Vs Atoi

But now you have that magic number, 4, sitting there. (Magic numberrefers to a seemingly arbitrary number that’s stuffed somewhere into your code.) So a slightly better approach would be to enter this line:

C++ Stoi Not Declared

Now this line of code works, and here’s why: The sizeof the array divided by the sizeof each element in the array gives the number of elements in the array.