I am basically trying to store everything after a certain index in the array.
For example, I want to store a name which is declared as char name[10]. If the user inputs in say 15 characters, it will ignore the first five characters and store the rest in the char array, however, my program crashes.
This is my code
char name[10];
cout<< "Starting position:" << endl;
cin >> startPos;
for(int i= startPos; i< startPos+10; i++)
{
cout << i << endl; // THIS WORKS
cout << i-startPos << endl; // THIS WORKS
name[i-startPos] = name[i]; // THIS CRASHES
}
For example, if my name was McStevesonse, I want the program to just store everything from the 3rd position, so the end result is Stevesonse
I would really appreciate it if someone could help me fix this crash.
Thanks
Suppose i is equal to 3. In the last iteration of the loop, i is now equal to 12, so substituting 12 in for i, your last line reads
name[12-startPos] = name[12];
name[12] is out of bounds of the array. Based on what you have shown so far, there is nothing but garbage stored in name anyway before you start doing this assignment, so all you're doing is reorganizing garbage in the array.
Please in future: post full compilable example.
A simple answer is that your array maybe is out of bound, since you don't provide full example its hard to know exactly.
Here is a working example:
#include <iostream>
using namespace std;
int main() {
int new_length, startPos;
int length = 15;
char name[15]= "McStevesonse";
cout<< "Starting position:" << endl;
cin >> startPos;
if(new_length <1){ // you need to check for negative or zero value!!!
cout << "max starting point is " <<length-1 << endl;
return -1;
}
new_length=length-startPos;
char newname[new_length];
for(int i= 0; i<new_length; i++){
newname[i] = name[i+startPos]; // THIS CRASHES
}
cout << "old name: " << name << " new name: " << newname << endl;
return 0 ;
}
To put it simply, change this:
for(int i= startPos; i< startPos+10; i++)
To this:
for(int i= startPos; i<10; i++)
You should be fine with that.
Explanation:
At some point, when you use the your old loop, this name[i-startPos] = name[i] would eventually reach an array index out of bounds and causes the crash.
Don't forget to clean up/hide the garbage:
Doing so, would cause the output to produce some kind of garbage outputs. If you got a character array of 'ABCDEFGHIJ', and have chosen 3 as the starting position, the array would be arranged to 'DEFGHIJHIJ'. In your output, you should atleast hide the excess characters, or remove by placing \0's
Related
Up until now I've been studying C, and now i wanted to try C++. Started out with some easy tasks. But I can't seem to find the answer, why is there a number either 0 or 488834... printed out.
I've tried re-declaring variables, using
for(n-1; n>=0; n--){
cout << a[n] << endl;
}
int main(){
int var = 0;
int a[100],n;
cin >> n;
for(int i=0; i<n; i++){
cin >> a[i];
var++;
}
for(var-1; var>=0; var--){
cout << a[var] << endl;
}
Everything works, except that 0/some number in the middle of the output
Result
In the following line:
for(var-1; var>=0; var--){
var-1 doesn't actually modify the value of var. So var gets to keep its original value, which means the first value you end up printing is what is after the end of the original sequence.
Use var = var - 1 instead.
In your second for loop you don't have an assignment, just a statement. You start printing from a location of the array that contains an invalid number due to this, you may want too have your second loop read
for(var = var-1; var>=0; var--){
cout << a[var] << endl;
}
Now, there are more element ways to write this, but this is a fix that is needed in your code.
I have finished writing a program that included reversing, expanding and shifting arrays using the pointer requirement asked by the professor. Everything compiles but the answer from the expand function does not return what I wish: adding 0s after the old user input array which asks for the size of the array and the numbers you wish to put into the array. I think my problem may lie from the fact that I include a pointer on something that might not have a reference in the program. Below is my code:
// *numPtr refers to my old user input array and int tamaño is the size of the array
void expandArray(int *numPtr, int tamaño) {
int *nuevoArray = new int[tamaño *2];
for (int i = 0; i<tamaño; i++) {
nuevoArray[i] = numPtr[i];
}
for (int i = tamaño; i < (tamaño*2); i++) {
nuevoArray[i] = 0;
}
std::cout << nuevoArray << " ";
}
As I said, my theory of the code not compiling the way I wish is because I use the *nuevoArray and it has no reference in my main code, but then again, I am just a beginner with C++. I was thinking of just doing a vector, but I think I would not follow the pointer requirements placed by the professor.
If you want to print the contents of nuevoarray, just use a for loop like this:
for (int i = 0; i < (tamaño*2); i++) {
std::cout << nuevoArray[i] << " ";
}
std::cout << "\n";
Also, since you are using new[] to create the array, you should not forget to delete[] it!
you can print your array by using
for (int i = 0 ; i < tamano * 2 ; ++i) {
std::cout << nuevoArray[i] << " ";
}
std::cout << std::endl;
or in c++11
for (auto i : nuevoArray) {
std::cout << i << " ";
}
std::cout << std::endl;
PS: The std::endl will return to the start of the new line and flush the cout buffer.
Your code does appear to be allocating a larger array and correctly copying data from numPtr into the new array and also correctly filling the remainder of the new array with zeros.
You don't explicitly say what you expect this function to output, but I'm guessing you expect it to print out the contents of the new array, and that you believe there's a problem because instead of that, you're seeing it print something like "0x7fb46be05d10".
You're not correctly printing the array out. Instead you're printing the memory address of the first element out. If you want to see the contents, then you need to loop over the elements of the array and print each one out individually.
Here's a function showing one way of doing that:
#include <algorithm>
#include <iterator>
void printArray(int *arr, int n) {
std::copy(arr, arr + n, std::ostream_iterator<int>(std::cout, " "));
}
Now you can replace the line std::cout << nuevoArray << " "; in your existing code with printArray(nuevoArray, tamaño*2);
(Also it sounds like whoever is teaching you C++ should take a look at this presentation from the recent C++ conference, CppCon 2015: Stop Teaching C)
I am trying to output the values present in the array, that are accepted during runtime, onto the console. But when I run this program I get the 5 values in the array as the last value only.
For example: if i give 0 1 2 3 4 as the five values for this program then the output is shown as 4 4 4 4 4.
#include "stdafx.h"
#include<iostream>
using namespace std;
int main()
{
int arrsize = 5;
int *ptr = new int[arrsize];
*ptr = 7;
cout << *ptr << endl;
cout << "enter 5 values:";
for (int i = 0; i < arrsize; i++)
{
cin >> *ptr;
cin.get();
}
cout << "the values in the array are:\n ";
for (int i = 0; i < arrsize; i++)
{
cout << *ptr << " ";
}
delete[] ptr;
cin.get();
return 0;
}
Both of your loops:
for (int i = 0; i < arrsize; i++)
...
loop over a variable i that is never used inside the loop. You are always using *ptr which refers always to the first element of the dynamically allocated array. You should use ptr[i] instead.
A part from that, dynamic allocation is an advanced topic. I'd recommend sticking with simpler and more commonly used things first:
std::cout << "Enter values:";
std::vector<int> array(std::istream_iterator<int>(std::cin), {});
std::cout << "\nThe values in the array are:\n";
std::copy(begin(array), end(array), std::ostream_iterator<int>(std::cout, " "));
Live demo
Following issues I think you could tackle:
The first include can be omitted I think. Your code works without that.
You use cin.get(), not sure why you need that. I think you can remove that. Even the one at the very end. You could put a cout << endl for the last newline. I am using Linux.
And use ptr like an array with index: ptr[i] in the loops as mentioned in the other answer. ptr[i] is equivalent to *(ptr+i). You have to offset it, otherwise you're overwriting the same value (that is why you get that result), because ptr points to the first element of the array.
P.S.: It seems that if you're using Windows (or other systems) you need the cin.get() to avoid the console to close down or so. So maybe you'd need to check it. See comments below.
I am newbie to programming and I am trying to pass an array into a function and add all the elements together and return the sum. The problem is that I am getting a garbage value for the sum. I have researched on how to pass arrays to functions and I do not know if I'm supposed to use a pointer to pass arrays. I am not good with pointers anyways.
Here is my code
#include <cmath>
#include <cstdlib>
using namespace std;
float mean(int);
int sum(int ARRZO[5]);
int total;
int main()
{
int ARRZ[5];
char *inname = "example.txt";
ifstream infile(inname);
if (!infile) {
cout << "There was a problem opening file " << inname << " for reading." << endl;
return 0;
}
cout << "Opened " << inname << " for reading." << endl;
for(int i=0; i<11; i++)
{
while (infile >> ARRZ[i])
{
cout << "Value from file is " << ARRZ[i] << endl;
}
}
total=sum(ARRZ);
cout<<"the sum of the elements in the array is"<<total<<endl;
system("PAUSE");
return 0;
}
int sum(int ARRZO[])
{
int sumz=0;
for (int i=0; i<5; i++)
{
sumz+=ARRZO[i];
cout<<ARRZO[i];
}
cout<<sumz<<endl;
return sumz;
}
You are actually reading all the values from the file in ARRZ[0] because of the inner loop. By the time you get to i=1, you are at the end of the file, and not reading anything.
Remove one loop, and increment i when you have read successfully a value.
I'm not sure what you think this pair of nested loops is supposed to do:
for(int i=0; i<11; i++)
{
while (infile >> ARRZ[i])
{
cout << "Value from file is " << ARRZ[i] << endl;
}
}
But (as #aliexisdm pointed out) the inner loop reads the entire content of the file. What he didn't (at least directly) point out is that you're reading every one of those values into the first element of your array. Then you're getting back to the outer loop, incrementing i, and trying to read the file again -- but since the stream's failbit has been set, all your subsequent attempts at reading are guaranteed to fail.
After that, you add up the 5 items in the array, but since you haven't read anything into 4 of them (and never initialized its contents) you end up with the last item you read from the file + 4 garbage values, giving still further garbage as the result (well, usually anyway -- you really have undefined behavior, so the program could crash and burn instead, but with most current computers, you'll just get some meaningless number).
I, however, would advise changing the program a bit more than just removing one loop and incrementing in the loop that's left. Instead, I'd remove all the (explicit) loops, and make some attempt at making real use of what the standard library provides.
You can read the numbers from the file in one fell swoop:
std::ifstream infile(inname);
std::vector<int> ARRZ ((std::istream_iterator<int>(infile)),
std::istream_iterator<int>());
Then you can sum them all with std::accumulate:
int sum = std::accumulate(ARRZ.begin(), ARRZ.end(), 0);
Finally, you can print out the result:
cout << "The sum of the elements in the array is: " << sum << "\n";
Since, however, you only read the values from the file to add them together, you don't really need to store them at all. You could just add them together and print out the result:
cout << "The sum of the elements in the file is: "
<< std::accumulate(std::istream_iterator<int>(infile),
std::istream_iterator<int>(), 0);
The whole job reduced to one step...
First off, this is a "homework" question so vector libraries and string libraries are off limits. I'm trying to get to the basics of c++.
My intention with this code is to make and use an array of string arrays. A list of words in other words.
When I run this code I get a bunch of nonsense.
If there is a better way to make a list of words in c++, I would love to hear about it.
const int cart_length = 50;
const int word_length = 50;
int main()
{
char cart_of_names[cart_length][word_length];
float cart_of_costs[cart_length];
char name[word_length];
cout << "enter the name of the first item: ";
cin >> name;
for(int i=0; i<word_length; i++)
{
cart_of_names[0][i] = name[i];
}
cout << endl;
cout << "that is: ";
for(int x=0; x<word_length; x++)
{
cout << cart_of_names[0][x];
}
cout << endl;
return 0;
}
If the string entered is not 50 characters long (cart_length), then less than 50 characters will be valid in the name. You should have an if(cart_of_names[0][x]==0) break; in your second loop.
I don't exactly understand what you are looking for. Following code will help you to read and print a list of 50 words. Hope this would help you.
const int cart_length = 50;
const int word_length = 50;
int main()
{
char cart_of_names[cart_length][word_length];
float cart_of_costs[cart_length];
for(int i=0; i<cart_length; i++)
{
cout << "enter the name of the " << i + 1 << "th item: ";
cin >> cart_of_names[i];
}
cout << "that is: ";
for(int x=0; x < cart_length; x++)
{
cout << cart_of_names[x] << endl;
}
return 0;
}
Check out STLSoft's fixed_array_2d (and it's higher order siblings). There's a detailed discussion of how they're implemented for maximum performance in Matthew Wilson's Imperfect C++.
If you can't use std::string, at least look at the functions like strncpy() from C for your name copying. Also, you're forgetting that c-style strings are null terminated.
Unless you're forbidden to use STL (which would be just mean), just use std::list<std::string>. www.cplusplus.com has detailed descriptions and examples for those classes.
Otherwise, you're stuck with an array of char arrays: in that case, be prepared for a lot of buffer overflow errors. Look around on the above site for the char[] management functions (strncpy() and the like), they'll make your life a bit easier (but not a lot).
In C, the best way I found to conceptualize what you are trying to do is using an array of char*. Same effect, but if you start to work with it I believe you may find it is easier on the brain.
It looks pretty close to me. Strings in C are null-terminated, which means that the end of the string is indicated by a null character. In a sense, a string in C is really just an array of bytes.
When you do:
cout << "enter the name of the first item: ";
cin >> name;
If I enter the string "Book", in memory it'll look like something like:
|0|1|2|3|4|5..49|
|B|o|o|k|0|*HERE BE DRAGONS*
Well, really it will contain the ASCII values corresponding to those letters, but for our purposes, it contains those letters. There here be dragons is memory that that you didn't initialize, so it contains whatever garbage your platform sets it to.
So when you copy your string, you need to instead look for that 0 byte at the end of the string.
for(int i=0; name[i]!=0; i++)
{
cart_of_names[0][i] = name[i];
}
Then when you output it, you don't actually need to do it a character at a time. You can just do cout<<cart_of_names[0]. cout knows where the string ends because of that terminating null character.
If you use strcpy() instead of
cart_of_names[0][i] = name[i];
it may work better but I cringe just looking at all that code.
"If there is a better way to make a list of words in c++, I would love to hear about it."
Include #include <string> and use std::string. The std::string type is part of the C++ specification, I think.
#include <iostream>
#include <string>
int main(void) {
std::string list[7];
list[0] = "In C++";
list[1] = "you can use";
list[2] = "the `std::string` type.";
list[3] = "It removes";
list[4] = "many of the problems";
list[5] = "introduced by";
list[6] = "C-style strings.";
for (int k=0; k<7; k++) std::cout << list[k] << ' ';
std::cout << '\n';
return 0;
}