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.
Related
I'm new to the community and to coding as well. Right now I'm taking Intro to Computer Science at my CC and we're learning C++. Anyways, I have to create a program which asks the user for a number, which will be the size indicator of the array new_array. The program then asks the user to input the numbers one by one and afterwards, outputs them in reverse.
#include
using namespace std;
int main()
{
cout << "How many numbers?\n";
int numbers; // holds amount of numbers to be entered into array
cin >> numbers;
int new_array[numbers];
for(int counter = 0; counter < numbers; counter++)
{
cout << "Enter number " << counter << endl;
cin >> new_array[counter];
}
cout << "You entered: " << endl;
for(int i = numbers; i >= 0 ; i-- )
{
cout << new_array[i] << endl;
}
return 0;
}
I understand how to do this and for the most part, my program worked. It outputs the numbers entered in reverse just fine, but before it does so, it outputs large, strange numbers. For example, if the user enters 5 as the amount of numbers to be entered, and then enters 1, 2, 3, 4 and 6 as the 5 numbers respectively, the program outputs the number 4669476 first and then outputs the numbers in the array in reverse. Can anyone explain to me what I did wrong and how I could fix this? Thank you in advanced!
PS be gentle! I'm a newbie at this
This loop reads out of bounds:
for(int i = numbers; i >= 0 ; i-- )
{
If you follow i through in your head you will see that you output entries numbers through to 0, when in fact you should output entries numbers-1 through to 0.
An alternative patterns is:
for( int i = numbers; i--; )
Or you can use the fabled --> operator.
It would be possible to "simply" start from numbers - 1, however the loop pattern you have used would not work for an unsigned counter (because they are always >= 0). IMHO it is a good idea to use a pattern which works for all types; then you are less likely to make a mistake in future.
In your display for loop, you started from i = numbers which is out of the array's range. Since the array starts from 0 till size - 1, then you need to start from i = numbers - 1 all the way to >=0.
Because you start from array[numbers] which is not defined.
array[0], array[1], ... array[numbers-1] are defined.
In C arrays are stored from 0 instead of 1. So the last number is stored in array[4]
So when you're writing it out you should start an numbers - 1 instead of just numbers.
Because you are starting the index from out of range giving you garbage value.
your code should look some thing like this
for(int i = numbers-1; i >= 0 ; i-- )
{
cout << new_array[i] << endl;
}
It seems like I always come here to ask silly questions, but here it goes. As of right now I am in my first compsci course and we are learning c++. I've had an extremely basic introduction to c before, so I had thought I'd go above and beyond my current assignment. Now I was doing this just to showboat, I felt like if I didn't practice my previous concepts they would eventually fade. Anyways, on to the problem! I was supposed to write some code that allowed the user to input their initials, and a series of exams. Now this was supposed to accomplish three things: average the exams, print out the entered exams, and print out their initials. Well, what was a simple assignment, got turned into a huge mess by yours truly.
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
int main()
{
string uInitials;
float avgExam = 0, tExam = 0;
int aExams[10] = {'0'};
int i, nExam = 0, cExam;
cout << "Enter your three initials!";
cin >> uInitials;
do
{
cout << "Enter your exam(s) to be averaged. Enter 0 when complete!\n";
cin >> cExam;
aExams[nExam] = cExam; //I used this before nExam was incremented, in order to get nExam while it was '0' That way the first exam score would be properly saved in the first space
nExam++;
tExam += cExam; //This is just to add all the exams up to later calculate the average
}
while(cExam != 0);
avgExam = tExam/(nExam - 1); //subtracted '1' from nExams to remove the sentinel value from calculations.
cout << "The average for initials: " << uInitials << " is: " << avgExam << endl;
cout << "This average was obtained using the following scores that were entered: \n";
for(i = 0; i < (nExam+1); i++)
{
cout << aExams[i] << endl; //Used a for loop to prevent redundancy
}
return 0;
}
The previous is my code, and the problem is that I'm getting output errors where it adds two '0's when I print out the list of entered exams. Also I feel like I made the whole do{}while() loop one huge clunky mess, so I'd like to refine that as well. If anyone could assist this poor, ignorant, beginner I would greatly appreciate it. Thank you for your time!
Some advice that i can give is for example in the 5th line there is no need
to put the 0 between ' ' and not even need to use the assign = operator.
You can initialize the array like this:
int aExams[10]{0};
Which will initialize all elements to 0,but can't be used for other value.
For example you won't have all the elements with value 1 if you write
int aExams[10]{1};
If your intention to initialize all elements in an array is with value other than 0 you can use fill_n(); function.
fill_n(aExams, 10, 1);
The first argument is the name of the array, the second is up-to which element you want to be initialized with the third argument, and the third is the value you want all elements to have.
Do not leave uninitialized variables like in line 6 with cExam and i variables. Initialize it like cExam=0; (copy-assign initialization) or cExam(0); (direct initialization). The latter calls the constructor for int built-in type.
A negative i see in your do-while loop is that you do not make sure that the user will enter under 10 exams,bad things will happen if the user tries to input 15 exams in an array that can hold only 10.
Just change the while to something more like this:
while( cExam != 0 && (nExam<10) );
You can also write the first two lines of the do-while loop outside the loop.
It is needed only once to tell the user that to stop the loop he/she needs to enter 0. There is no need to tell them this on every iteration plus that you will have a good performance benefit if you put those two lines outside the loop.
Look here how i would write the code and ask if you have any questions.
http://pastebin.com/3BFzrk5C
The problem where it prints out two 0's at the end of your code is a result of the way you wrote your for loop.
Instead of:
for(i = 0; i < (nExam+1); i++)
{
cout << aExams[i] << endl; //Used a for loop to prevent redundancy
}
Use:
for (i = 1; i < (nExam); i++)
{
cout << aExams[i - 1] << endl; //Used a for loop to prevent redundancy
}
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.
Write a program to input a series of 12 integers from the keyboard and store them in a one-dimensional array, x[12], then displayed them on the computer screen in reverse order.
I have a basic understanding that:
My numbers in the array will go from {0 to 11}
I am using a for loop (which I don't currently know how to do)
Now... How do I write this program?
You would do this:
loop from 0 to 11 using a for loop (for(size_t i = 0; i < 12; i++))
for each i, std::cin into the item at index i std::cin >> array[i];
To print them out you can use a while loop with i--. It will stop when i is zero and it will be backwards.
Because this is a homework question, I won't give you the full code but I hope this answer helps.
Learn about loops: while for do, while etcetera and you just might find the solution that you have been looking for
Example:
for(i = 0; i < 10; i++){
cout << i;
}
Since you know the quantity of numbers, you could insert them into the array in reverse order:
cin >> x[11]; cin >> x[10]; cin >> x[09]; //...
Next you would display the array in normal order:
cout << x[0]; cout << x[1]; cin << x[02]; //...
Since I didn't use a for loop, that's not going to help, is it?
The key concept is the 3rd parameter of the for loop, which can control the direction of a loop.
Let us investigate some examples:
for (unsigned int i = 0; i < 10; i += 2) {cout << i << endl; }
The above loop skips items because the variable is incremented by 2. That is 2 is added to index variable. This shows that loops don't always have to use ++.
So, what would happen if the index were set to the end value and then subtracted each time?
for (int i = 10; i >= 0; i -= 2) {cout << i << endl;}
This is for you to figure out.
Now, you will need to either ask questions in class, ask the professor after class or get a book that you will read and can understand easily (in addition to the one you have).
I'm not sure how to title my question, but here goes. I am testing some features, and I have hit a snag.
What I want to know is how can I set up a "for" or "if" statement to only put values in an array that meet a criteria? For example, find every divisor for a number, but only put factors in an array.
Any help would be loved, source code can be provided if needed :). Yes, I am new, so be gentle!
#include <iostream>
using namespace std;
int main(){
int n;
int counter = 1;
cout << "What number would you like to use? ";
cin >> n;
int DiviArray[n];
for (int k=0,j=1;k<n;k++,j++)
{
DiviArray[k] = n-k;
}
int k = 3;
int factn[n];
cout << "Factors of " << n << ": " << endl;
for (int i=0, j=1;i<n;i++,j++)
{
factn[i] = n/DiviArray[i];
if(factn[i]*DiviArray[i]==n)
{
cout << counter << ". " << factn[i] << " x " << DiviArray[i] << endl;
counter++;
}
}
return 0;
}
EDIT: Decided to go with vectors, not sure if I can get it to work, but thanks for the feedback guys :)
Since you don't know in advance how many values will meet the condition, you should use a std::vector.
As a benefit, it keeps track of how many elements you've already added, so push_back will always use the next available index.
This also fixes
cin >> n;
int DiviArray[n];
which isn't legal C++.
If you only want to put the values into the array that match the condition, then you should only put a number into the array when the condition is matched. To do that, the statement that puts a number into the array has to be inside the if-block for the condition. I hope I don't need to explain why :)
This is the only time in your program where you actually do want two indices: one that is incremented every time through the loop (to count how many times to run the process), and one that is incremented only when you put a number in the array (to figure out where the next number goes). Everywhere else, you've created a completely useless j variable (the uselessness should be apparent from the fact that there is no code that actually uses the value, only code to set it).