find last char in std::string ERROR: Expression: string subscript out of range

Question

So, this returns an error on execution, no errors shown in the debugger.

Debug assertion failed!

Expression: String subscript out of range.

For information on how your program can couse an assertion failure, see the visual c++ documentation on asserts.

int main()
{
// declaring variables
string input = "";
int firstChar;

// process:
cout << "Please enter a valid sentence (with spaces):\n>";
getline(cin, input);

cout << "first char is " + input[0] << endl << endl;
firstChar = input.length();
cout << "last char is " + input[firstChar];

// stop and return success
getchar();
return 0;
}

Answer 1

input[firstChar] is attempting to access the byte one-pass the end of the character array input because arrays are indexed by [0, length).

The last character is actually input[firstChar - 1].

Just a little tip, use the stream insertion operator << instead of + because the latter yeilds a temporary std::string object.

Answer 2

You should test that in your input is a valid content before using it.Something like if(length(input)>0)....The user might not give the wanted data even if you typed what you need between () and validations are needed

Answer 3

C++ strings of length length are indexed from 0 to length - 1.