I'm doing work on a multifunction program for my programming class, and one of the functions requires that an array of strings be used.
The objective is to store 10 names in an array, and then have the user enter a number that randomly determines the 'winning' name.
The only problem is that, once I execute my code, the program crashes after completing the 10 loops to get the names. That's the main thing I'm trying to identify, what's causing the crash.
The entire program is much larger, but the relevant code is shown below.
string Name1, Name2, Name3, Name4, Name5, Name6, Name7, Name8, Name9, Name10, tempName, winName;
string array[10] = {Name1, Name2, Name3, Name4, Name5, Name6, Name7, Name8, Name9, Name10};
int tempNum = 0;
int winNum;
int userEntry;
int userSelection;
for (int test = 0; test < 11; test++)
{
cout << "Enter a name: ";
cin >> tempName;
array[tempNum] = tempName;
tempNum++;
}
//The program crashes at this exact spot, right after collecting the 10th name
cout << endl;
cout << "Now choose a random number between 1 and 100: ";
cin >> userEntry;
winNum = static_cast<int>(userEntry * 3.14159 + 12.7 * 10) % 10;
winName = array[winNum];
cout << endl;
cout << "The winner of the game is" << winName << "!" << endl;
In the for loop you are trying to access to array[10] and that does not exist since array has only 10 elements, from 0 to 9. That's why your program is crashing.
Change the condition in your for loop from for (int test = 0; test < 11; test++) to for (int test = 0; test < 10; test++) and it should works.
Your array has 10 elements and and you are accessing 11 elements, 0 to 10, which is causing your program to crash. Because your code is accessing a location which doesn't belong to your program. Change the condition in for loop from test < 11 to test < 10.
Use "at" function of string class if you can, it throws an exception when you try to access out of bound subscripts.
Two problems.
One, you're instantiating an array with 10 elements then looking up its 11th element.
Firstly, change the if condition from test < 11 to test < 10.
This will solve your crash.
Secondly, your program could crash for large inputs.
When you initialize the string array, the compiler assigns a certain amount of memory to the array.
The amount of memory allocated to array is determined by the compiler.
The compiler determines the size of each of the string variables, and multiplies it by 10 to get the total size needed by the array, and allocates that much memory accordingly.
While strings can resize dynamically, arrays do not. The array has a fixed amount of memory allocated to it.
Hence, if during input of the strings that you save into the array by overwriting its indices, you could write into the array more characters than it can hold.
The amount of memory that will be allocated is implementation dependent since the default capacity of a string is implementation dependent.
A simple workaround would be to define the name strings to a large string at the beginning like string Name1 = "-------------------------";
This way the user input is most likely smaller in size that the initial value.
Related
I'm creating a simple quick sort program that initializes an empty array and asks the users for inputs to determine how many elements are going to be sorted and what elements are going to be sorted.
The problem I am encountering is a local variable is being changed despite being only being referenced to once assigned. Attached below is the code.
int main()
{
int amount;
int numbersarray[] = {};
std::cout << "How many numbers do you want to sort? " << std::endl;
std::cin >> amount;
for(int i = 0; i <= amount; i++){
std::cout << "Enter number to be sorted: " << std::endl;
std::cin >> numbersarray[i];
}
std::cout <<"Amount to be sorted: " << amount << std::endl;
for(int i = 0; i <= amount; i++){
std::cout << numbersarray[i] << std::endl;
}
}
What I expect to be occurring, when I input the amount as 5, I should be able to input 5 elements into the array, instead however the Amount printed is 2 and the maximum elements I can put into the array is 3.
Below is the execution output.
How many numbers do you want to sort?
5
Enter number to be sorted:
5
Enter number to be sorted:
2
Enter number to be sorted:
5
Amount to be sorted: 2
5
2
5
I've tried messing around with the for statement but I don't think I'm doing it right as it hasn't fixed the problem, The manipulation of the for statement I'm doing is changing the condition (i.e !=, <, <=)
You have undefined behavior. Anything can happen. Local variable can change without reason, the program can crash and your computer can format itself with linux 6.9
There are many problem. The first is that your program is invalid according to the standard:
int numbersarray[] = {};
This is not valid. Array need a size:
constexpr int max_amount = 32;
int numbersarray[max_amount] = {};
If you need it to be dynamic, use vector:
std::vector<int> numbersarray;
numbersarray.resize(amount);
Second, you have another source of undefined behavior:
// Iterates too much, numbersarray[amount] is past the end
// ~~~v~~~~~~~
for(int i = 0; i <= amount; i++){
std::cout << "Enter number to be sorted: " << std::endl;
std::cin >> numbersarray[i];
}
It should be:
for(int i = 0; i < amount; i++){
std::cout << "Enter number to be sorted: " << std::endl;
std::cin >> numbersarray[i];
}
To avoid invalid code and undefined behavior, you should enable warnings.
numbersarray is a C-style array with a size of zero and doesn't adjust its size dynamically (most compilers might even fail to compile int numbersarray[] = {}; since an empty initializer isn't allowed for an array with unspecified size).
Writing or reading its elements causes undefined behaviour (which can be access violations, changing unrelated variables, and much more). This is the reason why you might see the values of local variables changing. Someone else that uses the same code could get completely different behaviour, since it is undefined.
I'm just practicing using arrays. So my program consist of inputting numbers of data type double into the array and have them print out. Simple.
I only limited the numbers down to 4. So the array, num_List[3] is in the code. I've made sure to use the for loops properly for reading and printing out the result.
The first few times I tested the code. I realized that the 4th number in the array was in scientific notation, telling me that I forgot to initialize the array to 0, in this case 0.0, since I'm using double. So I put in this code.
for (index = 0; index <= 3; index++)
num_List[index] = 0.0;
This code should have initialized the arrays of num_List to 0.0. However, when I tested this, nothing came up, after I inputted the 4 numbers. So I made a logical error here or it's something else with the for loop that's causing it to be trapped and not continue the execution.
I've read in the books about this particular way to initialize.
#include <iostream>
using namespace std;
int main() {
double num_List[3]; // These are my variables
int index;
//double num; // Ignore these two for now, for they are to be modified later on.
//double result;
cout << "This program will summarize the numbers you've inputted print out the result. \n";
cout << "And also print out the address of the 1st and 4th address in the array." << endl;
cout << "Please enter the four numbers to be summarized.";
for (index = 0; index <= 3; index++) { // I put this in after I realized my mistake of not initializing my arrays to 0.0.
num_List[index] = 0.0;} // This is where the problem is, I think.
for (index = 0; index <= 3; index++) // This reads in the user the input
cin >> num_List[index];
cout << "The numbers you have inputted is:\n";
for (index = 0; index <= 3; index++) // This prints out the array.
cout << num_List[index] << ", " << endl;
return 0;
}
If you focus on the aforementioned code, and try to compile it, you'll see that my code unfortunately doesn't continue on from there after you input 4 numbers, regardless of whether or type a number and space it up to 4 numbers, or input a number, press the enter key for those numbers. Most likely I've made a obvious mistake, but I'm having some trouble seeing it.
I use Code Blocks, so things are a little different compared to the Bloodshed C++ compiler I used to use to practice codes on.
double num_List[3];
This declares an array with 3 elements, indexed 0 through 2.
for (index = 0; index <= 3; index++)
This loops through 4 indices, 0 through 3. When you do something with num_List[3], you get undefined behavior. In your trial, the undefined behavior fortunately resulted in just some garbage output.
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Here it is:
#include <iostream>
#include <cstdlib> // for rand() and srand()
#include <ctime>
using namespace
int main()
{
//cout << "How many players?" << endl;
int numplayers=1;
//cin >> numplayers;
int players[numplayers];
int x=0,y=0;
srand(time(0));
x=(rand() % 6 + 1);
y=(rand() % 6 + 1);
players[1]=players[1]+x+y;
cout << ("Your score is" + players[1]) << endl;
cin >> numplayers;
}
Ok My original problem was that this always crashed, now it prints "#"???
C++ arrays are 0 based.
players[1] is accessing a location outside the range of the array.
You will want: players[0].
cout << ("Your score is" + players[1]) << endl;
Here you're trying to use direct string concatenation, but you can't concatenate a string literal with an integer like that. You end up doing pointer arithmetic, which is definitely not what you intended.
You should instead use cout's built-in formatting:
cout << "Your score is" << players[1] << endl;
Your next problem is that players is not declared correctly; an array cannot have runtime bounds, and numplayers (despite having only the one initial value) is ultimately a "runtime" variable. You would be better off with a std::vector if the size of the array is going to change later; otherwise make numplayers a constexpr.
Your last problem is that, if the array declaration were valid, you'd be trying to access the second element of a one-element array! The first element is players[0], not players[1].
There are many things you're doing not good.
I believe you're using C++, there is no known way to me about creating arrays of dynamic size i.e. int players[numplayers]. In C++ either we can create array of fixed size i.e. int players[10] or use pointer to an array for dynamically allocated memory e.g. int* players = new int[numplayers]. This allocates an array of size numplayers and an int pointer named players is pointing to it. We can use this pointer as normal array e.g. printing 1st index of array is written as player[0] or another syntax is *(player + 0). Remember to delete this dynamically allocated memory at the end of program i.e. delete[] player.
Second thing is when you have allocated an array and are using its value for computation, always initialize it to 0 as newly allocated array contains garbage value and it will affect your computations. code for initializing it to zero may be like this:
Here is the loop:
for(int i = 0 ; i < numplayers ; i++){
player[i]=0;
//another syntax is : *(player + i) = 0;
}
C++ does not concat as you did in your std::cout statement. Make it like this:
cout << "Your score is" << players[0] << endl;
In C++, arrays always start with index zero, so 1st index will be 0 in this case. So your program will work well if it is like this:
int numplayers = 1;
int* players = new int[numplayers];
int x = 0, y = 0;
srand(time(0));
x = (rand() % 6 + 1);
y = (rand() % 6 + 1);
players[0] = 0;
players[0] = players[0] + x + y;
cout << "Your score is" << players[0] << endl;
delete[] players;
return 0;
Definitely it crashes for the below line:
players[1]=players[1]+x+y;
Because size of players array is 1, so it has only index 0. And in above line, it tries to access index 1. Take a look at Buffer Overflow and array index out of bounds.
Try to define an array with constant size.
If you need a dynamic array, use linked list or vector.
I want to cout my string, everything works as it should, but when the string is shown, it immediately shows me the "example_4578.exe has stopped running" error. I have noticed that the problem is in the i < str[32].length part, because when I change it to i < 3, it works without any problem. How should I solve this?
std::string str[32];
cin >> str[1];
cout << "str[1]=" << str[1] << endl;
cin >> str[2];
cout << "str[2]=" << str[2] << endl;
for (int i = 0; i < str[32].length; i++)
{
cout << str[i];
}
EDIT 1.
I've made a huge mistake. I actually want to find the "number" of elements/words in "str". In my example, I have only designed two cins. But I actually want to design a "for" loop later on, so that the user can input as many words as he wants, so if he inputs 4 words, I want that code to return those number of words to me. How should I do this? In other words, how can I find out how many elements are in "str"?
Couple of things:
C++ is 0-indexed. What this means is that std::string str[32] has indices that go from 0 to 31, and str[32] should not be accessed. This will cause a crash.
str[31].length() (which is presumably what you wanted) is the length of the last string, not the length of the array. The length of the array is 32, and your loop should read for(int i = 0; i < 32; i++).
The main problem is that you are accessing an element (number 32) that is out of the bounds (0 - 31). To solve this problem and not repeat it again in the future use a range-for loop:
std::string str[32];
for (auto s : str)
std::cout << s;
str[32].length is not what you think.
I guess you meant somthing like: length of a 32-elements array. Right?
What you've written is pointer to funciton length of 33rd element of array.
This is because the types are:
std::string str[32]; // `str` is 32-element array of `std::strings`
str[32]; // `std::string` taken from 33rd position in array `str` (arrays' indexing starts at 0)
std::string has a member function named size_t std::string::length(). When referenced by name, you get its address.
To achieve what you wanted, you'd need to write:
for (int i = 0; i < 32; i++) {
cout << str[i];
}
Unfortunately, plain arrays don't have length (or anything similar) built in. So, you'd either need to use a constant, or (better) use a container, such as std::vector.
Again, I'm trying to make a simple program. It will read some kind of board, at the size of RxC. Each items on the board are letters, separated with spaces. This is a sample board:
A B C
D E F
G H I
After that, it will read an integer N, and for next N lines, read a string and process them one by one based on the given board. But now, I'm facing a problem with how to read them. Here is the code :
#include<iostream>
using namespace std;
int r,c,el; char **arr;
int main()
{
char *tes;
int n;
//start reading the puzzle
cin >> r >> c; el=r;
cout << el << endl;
arr = new char * [3*(r+c)-6];
for(int i=0;i<r;i++)
{
arr[i] = new char[c+1];
for(int j=0;j<c;j++) cin >> arr[i][j];
arr[i][c] = '\0';
}
for(int i=0;i<el;i++) cout << arr[i] << endl;
cin >> n;
while(n>0)
{
n--;
cin >> tes;
cout << tes << endl;
}
}
I don't know what's wrong with this, it's seems OK to me. However, it always get runtime errors. I'm using latest MinGW and gdb debugger. On gdb I saw something like
"received signal SIGSEGV. Segmentation
fault"
, and an 0xC0000005 error. I really have no idea what's going on here. I've tried both iostream(cin&cout) and cstdio(scanf,puts,etc.)
P.S.: I declare the variables globally, because I will process them on a different function out of the main() function. I set the size of the "height" of the array to (3*(r+c)-6), not to the normal (r) is because I will use the same array to store another strings later.
In addition to the problems already noted by others, you haven't allocated any memory for tes - it's just a dangling pointer.
Change:
char *tes;
to, e.g.:
char tes[80];
A board of size R*C needs, not very surprisingly, r*c chars of storage. I fail to understand why you're allocating the board in so many steps. A single char* board = new char[r * c]; should do it, then just keep track of where in the array your're reading.
Segmentation fault usually means you are trying to access memory which hasn't been allocated, for instance
char* mystr = (char*)malloc(3*sizeof(char));
mystr[4] = 0.0;
will (most likely) cause a seg fault because you're accessing memory which you didn't allocate (mystr goes from 0 - 2).
Are you sure you're allocating the memory correctly? I'm not sure why you have 3*(r+c)-6.
Further to unwind's answer, your array has size 3*(r+c)-6, but you are looping over values i = 0; i < r;, which depending on the values may just run out of bounds (plus it makes no sense).