#include <iostream>
using namespace std;
int main()
{
int loop = 0;
int Pass = 0;
int guess = 0;
cout << "Write In A 4 Digit Number!";
cin >> Pass;
while (loop == 0)
{
guess = guess + 1;
if (Pass == guess)
{
cout << "Your number is" + guess;
}
}
return 0;
}
This mystery code is giving me random outputs. This is a program ment to guess what number you put in. Instead when you input a random number and hit enter it gives you stuff like error and YF and stuff. Try it yourself by testing the code. If you type in 1 and press enter you will get our number is printed out.
our number is
ur number is
r number is
number is
number is
There's some more odd also like if you enter 666 you will get: e::_S_normalize_catory catory not found and if you enter 333 ☻ will print out.
There's plenty more. Some numbers are blank but some are not.
Can someone please tell me why this happends!
CLOSED: THANKS FOR HELPING ME OUT. I CLOSE THIS NOW. YOU CAN STILL CHAT!
You need to change the
cout << "Your number is" + guess;
to
cout << "Your number is " << guess;
In C++, adding a number to a string literal doesn't convert the number to a string; it does something else entirely (pointer arithmetic).
For a backgrounder on pointer arithmetic in C and C++, see Everything you need to know about pointers in C (especially the last section about strings).
The reason your program prints out funny strings is that, once guess gets large enough, the "Your number is" + guess points to some memory after the end of the string literal, and the program prints out whatever happens to be in that memory. (Technically, you're in the realm of undefined behaviour and so your program could legitimately behave in all sorts of strange ways.)
"Your number is" is a char *, and you are adding 'guess' to it. This moves the pointer to somewhere other than the start of the string literal. If the value of guess is small you will end up somewhere inside the string and it will print the subsequent part ok. If you enter a larger number it will access somewhere completely random and cause an error.
Try:
cout << "Your number is: " << guess;
(To use the string + operator at least one part of the input needs to be a string. You have a const char * and an int, so the compiler thinks you want to do pointer arithmetic. Even if you make the string literal into a string you would also need to make guess into a char * using itoa for it to display correctly. Much easier to stick with the stream version using <<.)
By adding an integer value to the address of the string ("Your number is" + guess), you get a new address that points to some character inside the string or to what comes next. Then the cout statement will print all characters from there until the next null byte.
You rediscovered the joys of buffer overflow hacking...
Related
I was using character arrays to get inputs from the user then display the output afterwards. However, every time I enter values with spaces in between, only the first word before the space is printed.
For instance, this is what I typed:
Customer No.: 7877 323 2332
This will be the output:
Customer No.: 7877
I already searched for possible solutions but I can't seem to find the right solution.
This is my code for reference:
#include<iostream>
using namespace std;
int main()
{
char custNum[10] = " "; // The assignment does not allow std::string
cout << "Please enter values for the following: " << endl;
cout << "Customer No.: ";
cin >> custNum;
cout << "Customer No.: " << custNum << endl;
}
Another option is to use std::basic_istream::getline to read the entire string into the buffer and then remove the spaces with a simple for loop. But when using plain-old character arrays don't skimp on buffer size. It is far better to be 1000-characters too long than one-character too short. With your input, your absolute minimum size of custNum is 14 characters (the 13 shown plus the '\0' (nul-terminating) character. (rough rule-of-thumb, take your longest estimated input and double it -- to allow for user-mistake, cat stepping on keyboard, etc...)
In you case you can simply do:
#include <iostream>
#include <cctype>
int main() {
char custNum[32] = " "; // The assignment does not allow std::string
int wrt = 0;
std::cout << "Please enter values for the following:\nCustomer No.: ";
if (std::cin.getline(custNum, 32)) { /* validate every input */
for (int rd = 0; custNum[rd]; rd++)
if (!isspace((unsigned char)custNum[rd]))
custNum[wrt++] = custNum[rd];
custNum[wrt] = 0;
std::cout << "Customer No.: " << custNum << '\n';
}
}
The two loop counters rd (read position) and wrt (write position) are simply used to loop over the original string and remove any whitespace found, nul-terminating again when the loop is left.
Example Use/Output
$ ./bin/readcustnum
Please enter values for the following:
Customer No.: 7877 323 2332
Customer No.: 78773232332
Also take a look at Why is “using namespace std;” considered bad practice? and C++: “std::endl” vs “\n”. Much easier to build good habits now than it is to break bad ones later... Look things over and let me know if you have questions.
Apart from std::getline, if you are going to use C-style strings, try the following code:
int main() {
char* str = new char[60];
scanf("%[^\n]s", str); //accepts space a a part of the string (does not give UB as it may seem initially
printf("%s", str);
return 0;
}
Also, if you absolutely need it to be a number, then use atoi
int ivar = std::atoi(str);
PS Not to forget gets (!!dangerous!!)
char* str;
gets(str);
puts(str);
cin >> int_variable will stop reading input when it reaches the first character that isn't a valid part of a number. C++ does not consider spaces part of a number, so it stops reading as soon as it encounters one.
You could use std::getline to read into a string instead, then remove the spaces from the string before converting to an integer. Or maybe in this case you don't even need the integer and can leave it as a string.
Hello everyone I'm having trouble with strlen and arrays, it keeps saying my string length is only one? If anyone could help it would be great here's my code:
#include <iostream>
using namespace std;
#include <cstring>
int main()
{
char word1[20];
int len = strlen(word1);
cout << "enter a word!\n";
cin.get(word1, 20, '\n'); cin.ignore(50,'\n');
cout << len;
}
Just read the back and forth in the comments, updating my answer to try and give some more intuition behind what's going on.
char word1[20]; Sets a place in your computer's memory that can eventually be filled by data up to 20 characters. Note that this statement alone does not "clear" the memory of whatever is currently there. As sfjac has pointed out, this means that literally anything could be in that space. It's highly unlikely that whatever is in this space is a character or anything your code could readily understand.
int len = strlen(word1); Creates an integer and sets it equal to the value of the number of characters currently in word1. Note that, because we have not specified any content for word1, you're taking the length of whatever happened to be in that memory space already. You've limited the maximum to 20, but in this case, whatever data junk is in there is giving you a length of 1.
cout << "enter a word!\n"; Prompt the user for a word
cin.get(word1, 20, '\n'); cin.ignore(50,'\n'); Get the word, store it in word1. At this point, word1 is now defined with actual content. However - you've already defined the variable len. The computer does not know to automatically redefine this for you. It follows the steps you provide, in order.
cout << len; Print the value stored in len. Because len was created prior to the user entering their data, len has absolutely nothing to do with what the user entered.
Hope this helps give you some intuition that will help beyond this one question!
#Chris is correct but perhaps a small explanation. When you declare a character array like char word1[20] on the stack, the array will not be initialized. The strlen function computes the length of the array by counting the number of characters from the address of word1 to the first null byte in memory, which could be pretty much anything.
I highly recommend using std::string for text.
If you must use character arrays:
Define a named identifier for the capacity.
Define the array using the named identifier.
The capacity should account for a terminating nul, '\0', character to
mark the end of the maximum text length.
Using the above guidelines you have the simple program:
int main(void)
{
std::string a_word_string;
std::string line_of_text_string;
const unsigned int c_string_capacity = 32U;
char c_string[c_string_capacity];
// The std::string functions
cout << "Enter some text: ";
getline(cin, line_of_text_string); // read a line of text
cout << "\nEnter a sentence: ";
cin >> a_word_string;
cin.ignore(10000, '\n'); // Ignore remaining text in the buffer.
// The C-style string functions
cout << "Enter more text: ";
cin.read(c_string, c_string_capacity);
c_string[c_string_capacity - 1] = '\0'; // Insurance, force end of string character
cout << "You entered " << (strlen(c_string)) << " characters.\n";
return EXIT_SUCCESS;
}
The std::string class is more efficient and can handle dynamically size changes.
The length of the array is the value of c_string_capacity which was used when defining the array.
The length of the text in the array is defined as strlen(c_string), which is the number of characters before the terminating nul is found.
You have to calculate len after reading in word1, otherwise you are left with undefined behaviour.
char word1[20];
cout << "enter a word!\n";
cin.get(word1, 20, '\n'); cin.ignore(50,'\n');
int len = strlen(word1);
cout << len;
It's a good idea to always initialize objects when you declare them. Since objects inside of a scope are not guaranteed to be initialized.
In C++11 for example, you can do this:
char arr[10]{}; // this will initialize the objects in the array to default.
char arr[10]{0}; // the same.
I'm reading C++ Primer Plus (6th Edition) and I've come across some sample code in chapter 4 which I have a question about:
Listing 4.2 strings.cpp
// strings.cpp -- storing strings in an array
#include <iostream>
#include <cstring> // for the strlen() function
int main()
{
using namespace std;
const int Size = 15;
char name1[Size]; // empty array
char name2[Size] = "C++owboy"; // initialized array
// NOTE: some implementations may require the static keyword
// to initialize the array name2
cout << "Howdy! I'm " << name2;
cout << "! What's your name?\n";
cin >> name1;
cout << "Well, " << name1 << ", your name has ";
cout << strlen(name1) << " letters and is stored\n";
cout << "in an array of " << sizeof(name1) << " bytes.\n";
cout << "Your initial is " << name1[0] << ".\n";
name2[3] = '\0'; // set to null character
cout << "Here are the first 3 characters of my name: ";
cout << name2 << endl;
return 0;
}
The code itself doesn't cause any confusion, but I've been running it through and I'm confused by a certain scenario.
name1 is initialised as an array of chars 15 elements in length - am I right in thinking this should hold a string 14 characters in length? The end char should be reserved for the string terminator, right?
If I enter my name as HowCanIPossiblyFitThisEntireStringIn?, I get the following output:
Howdy! I'm C++owboy! What's your name?
HowCanIPossiblyFitThisEntireStringIn?
Well, HowCanIPossiblyFitThisEntireStringIn?, your name has 37 letters and is stored
in an array of 15 bytes.
Your initial is H.
Here are the first 3 characters of my name: C++
How is the entire name I enter being stored? If I step through the code, after cin reads into name1, Visual Studio tells me it contains elements 0 - 14, with the last one being the char 'y' ("HowCanIPossibly...). I would assume from this that any extra data entered had been truncated and lost, but this is obviously not the case as the following cout successfully writes the entire name out to the console.
For curiosity's sake, could anyone enlighten me as to what's happening here? For the record, I'm using Visual Studio 2012 Express.
You are writing past the bounds of the array. The C++ standard doesn't say this should be an error; it says it is undefined behaviour. This means anything can happen, including seemingly working correctly. Simply put, your code does not have well-defined behaviour and so you shouldn't trust it to work.
We can imagine why it's probably working though. The first 15 characters will fit nicely into the array:
|H|o|w|C|a|n|I|P|o|s|s|i|b|l|y|F|i|t|T|h|i|s|E|n|t|i|r|e|S|t|r|i|n|g|I|n|?|...
^ ^
| These characters fit |
in the array
The rest of the characters are being written to the following memory locations. Now, remember that the null character, which is used to terminate C-style strings, is defined to have a representation that is all 0 bits. Now if the location following the location that contains the ? has all 0 bits in it, the string will appear to be null-terminated.
But the fact is, this is undefined. It just happens to work. Unfortunately, this is the scariest type of bug because it can seemingly work for a long time until one day you start getting calls from your very, very angry client.
You could use istream::get with the buffer and the size of the buffer:
cin.get(name1, Size);
As others have noted, it's far easier to use std::string:
std::string name1;
cin >> name;
I use Visual C++ 2010 Express Edition to compile and run the .exe files I write in the C++ programming language. I am trying to create a loop-based logic using C++ to ask the user how many entries he chooses to enter, and ask questions limited to that no. of entries. For example I want to output, "How many characters do you wish to enter?: " Say the user gives the answer as '3' which is stored in the int variable 'entries'. I then want to keep asking the question 3 times before it stops and continues with the next line of code. I hope you understand, here is a block of code to demonstrate what I am doing:
#include <iostream>
#include <string>
using namespace std;
int main()
{
cout << "How many values do you need to enter?: ";
int entries;
cin >> entries;
int offset, number;
string valueName[50];
float valueValue[50];
for (offset = 0; offset < entries; offset++)
{
cout << "Enter " << number << " Value Name: ";
cin >> valueName[offset];
cout << "Enter " << valueName[offset] << "\'s value: ";
cin >> valueValue[offset];
for (number = 1; number <= entries; number++)
{
}
}
char response;
cin >> response;
return 0;
}
Strangely when I run this simple program, it fails when I enter the value's name to be inserted into the 0th element of the valueName[] array. It just pauses the execution of the program and a dialog box pops up saying "Runtime Check Failure #3 - Variable 'number' is being used without being initialized!" Another problem regarding this program is that, for quite some time, when I ran this program this "Runtime Check Failure #3" box never appeared, and when it didn't, the number value went wrong, and first started with 1, and then for the next loop jumped to 6, and then repeated 6 again for the next loop! Please help me! I've checked online scouring this problem everywhere, but it just doesn't apply to my type of problem! Is it because the variables are out of scope? But they're declared outside the for loops right? So please help me!
The runtime is telling you the truth, the following line comes after you have declared number as an int but have not given it a value.
cout << "Enter " << number << " Value Name: ";
In your code you declare the following, in C++ this means give me 2 ints but the values are not defined yet, e.g.
int offset, number;
Change it to something like this ..
int offset = 0;
int number = 0;
You are printing the variable number without assigning to it first, i.e. it's uninitialized. When it prints some random number it's because that what happens to be in the memory at the time you run the program. Assign a value to it before you use it.
The problem is exactly the error message you're getting. You're using the variable number without initializing it.
You use the variable right here, at the top of your loop, when it hasn't been initialized to anything yet:
cout << "Enter " << number << " Value Name: ";
What is your intention with the number variable? It doesn't really seem to be serving any purpose. If you want to print which entry you're currently on, you could use the offset variable instead, like this:
cout << "Enter " << offset << " Value Name: ";
But that still seems a little unclear to me.
But the reason that you're having a problem is because the value is uninitialized, so you're experiencing undefined behavior. This is also the reason that Visual Studio doesn't always catch it; it will probably always catch in Debug mode, but in Release mode it will almost never catch it. You need to initialize all your variables before you use them.
In my case it was because an extern variable was declared twice.
I've come this far without asking for help, but I've got a problem that I can't seem to fix. I like cryptology, so now that I am learning C++, I want to make programs to encrypt and decrypt strings. I read that the best way is to convert the text to ASCII and go from there, so here is a simple program I made in C++ to try and convert a char variable to ASCII:
#include <iostream>
#include <string>
#include <math.h>
using namespace std;
int main()
{
char strString[1000];
cout<<"Enter you message:"<<endl;
cin>>strString[1000];
string strEncrypt;
int a = 0;
while (strString != '\0')
{
int b = (int)strString[a];
strEncrypt.at(a) = b; //This is where I'm getting an error.
a++;
}
cout<<"Encrypted message:"<<endl;
cout<<strEncrypt<<endl;
}
So, I've tried all 3 things I know to do to troubleshoot (Google, check for missing simicolons, and make sure I'm doing == not =, but this is just something I don't know how to do, not something I'm forgetting (I hope). So, any help would great!
You don't have to change the characters to ASCII they already are. Chars are basically the same as integers in memory.
Now to your question; . If you want to set a character in a string you can do that like this
string[index] = b;
Another thing to be careful for in your code. You are using cin to read the string from the user. This will not let you read messages that have spaces in them and will only read the first word. For example, if the user enters "Love Crypto" cin will only read "Love" and "Crypto" will be ignored. To get the entire line, use getline instead.
As for looping over characters in a string, it's better to do it as follows:
for(int i = 0; i < strString.length(); i++)
{
strString[i] = bla;
}
Again, you're code isn't actually doing anything. It is only reading a letter and then storing a "letter" in another string.
string::at() throws exception if the index passed to at() is out of range. So, if you are getting runtime error then it's expected. Because, your string strEncrypt is initialized to "" and thus the size is 0.
You may try
strEncrypt.reserve(strlen(strString));
Easiest way to actually make the code you have work is change this line strEncrypt.at(a) = b; to this strEncrypt += b; Which will add the characters to the empty string strEncrypt.
Your code doesn't make much sense though as char types are already ascii. You'll have to explain more about what kind of encrypting you are trying to do and maybe we can point you in the right direction.
EDIT: After thinking about what you're trying to do a bit more based on the code you have it seems like you want to print the numeric ascii value of characters. You can do that with just a cast like this:
string input;
cout << "Enter you message:" << endl;
// handle spaces in the message
getline(cin, input);
cout << "String chars as ascii values:" << endl;
cout << "Char: " << "ASCII Code:" << endl;
for (int i = 0; i < input.length(); ++i)
{
// casting the char to an int with (int) will print the ascii code
cout << input[i] << " " << (int)input[i] << endl;
}
On top of the fact that your input is already in ASCII, keep in mind that doing cin >> strString[1000] doesn't limit the input captured to the length of your buffer unless you specifically specify the number of characters to capture for the stream object using setw() or setting it's ios_base::width data member. So your method right now risks buffer overflows.
Secondly, the form of cin >> that you're using will not capture the entire line of input. Instead it will stop at the first white-space or any other delimiting character (or end-of-file if that is reached first). In your case, if you are entering a line like "Hello World", then the syntax you're using will only capture "Hello" and drop "World".
A much better idea would be to use the getline() function with a std::string object if you are wanting to capture a line of input to a string and remove the delimiting newline character without risking buffer overflows ... for instance:
string strString;
getline(cin, strString);
Apart from advises given, when receiving this kind of run-time errors use Cppcheck utility.
It will give you the answer: "Message: Array 'strString[1000]' index 1000 out of bounds".