Trying to convert a string/char to an integer yielded an unexpected result

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I came across something strange. It is probably trivial but I can't find the answer. Can anyone explain to me why in this action I get a result of 49?

using namespace std;

int main() {
    int number;
    string binary = "10101011";

    number = int(binary[0]);
    cout << number; // result is 49 , why is that?    

binary[0] is '1', which has an ASCII value of 49.

Why do I get this unexpected result using atoi() in C?, atoi() converts a string representation of an integer into its value. It will not convert arbitrary characters into their decimal value. For instance: One of the main solutions is to use Integer‘s dedicated static method: parseInt(), which returns a primitive int value: @Test public void givenString_whenParsingInt_shouldConvertToInt() { String givenString = "42"; int result = Integer.parseInt(givenString); assertThat(result).isEqualTo(42); }

Because when you're trying to convert binary[0] element, which is of char type to int type - it converts char's ASCII code that is simply a number, as it was mentioned by @QuentinUK.

If you want to store bits and convert them to numbers, you should look at std::bitset.

If you want to get any element out of std::string as a number, you should look at std::atoi.

atoi() — Convert Character String to Integer, The atoi() function returns an int value that is produced by interpreting the input characters as a number. The return value is 0 if the function cannot convert the� In the following example, the user wants to convert the begin_date column of the tab1 table to a character string. The begin_date column is defined as a DATETIME YEAR TO SECOND data type. The user uses a SELECT statement with the TO_CHAR function to perform this conversion: SELECT TO_CHAR(begin_date, '%A %B %d, %Y %R') FROM tab1;

You have defined string binary = "10101011"; binary[0] is character '1'. When you parse a character to int, the output is ASCII value of the character.

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So actually in your code you are not printing that char in int but rather than you are printing ASCII value of '1' that is 49.

Whenever a char is converted to int it changes and assigns ASCII value of that char.

to solve your problem you can use folow:

#define conv_digit(ch) (ch-'0') 

Then just call this function passing binary[0] or whatever char you want.

String and character literals (C++), How to declare and define string and character literals in C++. You can also create std::string literals without having to perform extra construction or conversion steps. enables s-suffix for std::string literals int main() { // Character literals auto in a multicharacter literal, which can give surprising results. Every now and then you run into unexpected SharePoint behavior. The Title field of an item is a 'single line of text' field. In my specific case however this Title field contained a file number. Not a problem at all, BUT you get a really strange sort order when you start to sort numbers as strings. File number 1000 comes before file number 9.

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1.The actual return value of stoi function is of type int. So when its not able to convert,the compiler automatically throws an exception. 2.Like I said in the previous point, it throws an exception automatically so its not mandatory to use throw here.

When the above example fails to parse the string as a valid integer, you can see that we just set it to -1. This doesn't work too well if -1 one is a meaningful value in your program. Instead, we could parse the string and return a nullable int where the null value indicates that the input string was not a valid integer.

  • The character '1' has a numeric value of 49 in the ASCII character set. Although there are different character sets, ASCII or a related character set are used more often than not. Incidentally, there is no standardised character set in which the character '1' has a numeric value of 1.
  • Ok, so it's return ASCII value. What is a simplest way to change it from string "1" to int 1 ? I tried: number = stoi(binary[0]); but it return an error.
  • It yields an error, because binary[0] is a char, not a string. try stoi("1") or stoi(binary)
  • You can either use atoi(*char) or binary[0]-'0' - this basically subtracts ASCII of '0' with the ASCII of the character 'binary[0]'. The result is an integer.
  • @AdityaNagesh atoi has the disadvantage that you cannot distinguish error from valid input "0", so it only can be used if "0" is not acceptable input on application level, otherwise the function is not recommendable. Be aware, too, that subtracting '0' only is portable for digits of base 10 or less. Such operations on letters (e. g. determining case or converting to a different one) can fail as there are character sets where the letters are not arranged contiguously (most famous one being EBCDIC).
  • number = std::stoi(binary, nullptr, 2); for one bit number = binary[0]=='1';