The idea of my program was to print individual digits of n.
But instead it prints all the digits at once in the first line and a bunch of zeroes or garbage values in subsequent lines.
I want to access each individual number as we can do with arrays.
Suppose the input is 1234, why doesn't it print 1\n2\n3\n4?
#include <iostream>
#include <cmath>
#include <stdlib.h>
using namespace std;
int main()
{
int* n=(int*)malloc(1000*sizeof(int));
cin>>*n;
int len;
len = log10(*n) + 1;
for(int i=0;i<len;i++)
{
cout<<n[i]<<endl;
}
}
n is declared as a pointer to a memory location which can store 1000 integer entities. When you use cin>>*n;, an integer value is read as input and store at the first memory block among the 1000 blocks. The individual digits of the integer are not stored in separate blocks, hence you can't print them separately.
For example, if the input is 123,
n[0] stores 123, n[1],n[2],...n[999] stores junk values.
To store a value in n[1], you will have to use cin again.
For some reason you think that
int* n=(int*)malloc(1000*sizeof(int));
cin>>*n;
will read a number and put each digit in a different element of the dynamic array n. If that happened then the rest of your code would work (kind of). But of course it doesn't. Instead the number read is put into *n (or, same thing, n[0]) and the rest of the dynamic array elements are uninitialised, which explains the garbage values you see.
I'm struggling to understand why you thought your code might behave in the way you wanted. I guess you are just an optimistic person and think that if you wish hard enough the compiler will understand. This seems to be quite a common attitude among beginners. Unfortunately programming isn't like that.
When you cin >> *n, you don't read the number digit by digit, but read in as a whole.
So when you cin >> *n and type in 1234, *n becomes 1234.
If you want to print all the individual digits, like 1\n2\n3\n4, you need to separate the digits for yourself:
int pos = 1;
while (*n != 0)
{
n[pos] = n % 10;
n /= 10;
++pos;
}
for (--pos; pos > 0; --pos)
{
cout << n[pos] << endl;
}
However, the easiest approach is to read in the number as a string, not a number, then print out the characters, that is the digits, one by one.
char str[1000];
cin >> str;
for (char *s = str; *s; ++s)
{
cout << *s << endl;
}
You can also convert the number into a string, and do the same:
#include <cstring>
using namespace std;
...
char str[1000];
sprintf(str, "%d", *n);
for (char *s = str; *s; ++s)
{
cout << *s << endl;
}
------- Original Answer:
If you want to print the first element of n:
cout << *n;
or
cout << n[0];
Your code
for(int i=0;i<len;i++)
{
cout<<n[i]<<endl;
}
means
cout << n[0] << endl;
cout << n[1] << endl;
cout << n[2] << endl;
...
cout << n[len-1] << endl;
Related
I'm a beginner in programming and as you can see, I created a program where the user is asked to input three numbers. It will display the greatest among the numbers given. But after I finished the code, a question came into my mind, what if the user was asked to input a hundreds of numbers and should display the greatest among the numbers given. So the question is, is it possible to do that? what are the things I need to learn to produce that result? is there any hints you can give me?
#include <iostream>
#include <string>
using std::cout, std::cin, std::endl, std::string;
int main() {
string result = " is the greatest among the numbers given";
double x, y, z;
cout<<"Enter three numbers to decide which is the largest: "<<endl;
cin >>x;
cin >>y;
cin >>z;
system("clear");
if(x>y && x>z){
cout<< x << result;
} else if (y>z && y>x){
cout << y << result;
} else
cout<< z << result;
return 0;
}
With the program below, you can get as many numbers as you want from the user and find the largest of them.
#include <iostream>
int main()
{
int size=0, largestValue=0, value=0;
std::cout << "Enter total numbers you want to add :" << "\n";
std::cin >> size;
for (int i{ 0 }; i < size; ++i)
{
std::cout << "Enter value to add : ";
std::cin >> value;
if (i == 0 || value > largestValue)
{
largestValue = value;
}
}
std::cout << "Largest value = " << largestValue << "\n";
return 0;
}
One solution would be to store your inputs in a list and sort them afterwards. Just google "sorting alorithms". Also there are nice youtube visualizations.
Another one would be to not save the inputs into dedicated variables - in your case x, y, z - but to always save the largest given input:
int largestInput = std::numeric_limits<int>::min();
int input;
for (int i = 0; i < 10000; i++)
{
std::cin >> input;
largestInput = input > largestInput ? input : largestInput;
}
If you know the inputs are large, you can use vectors.
#include <bits/stdc++.h>
using namespace std;
int main(){
int total_num=0;
cout << "Enter total numbers:" << "\n";
cin>>total_num;
int max_number = INT_MIN;
vector<int> v;
for(int i=0;i<total_num;i++){
int x;
cin>>x;
v.push_back(x);
max_number = max(max_number,x);
}
cout<<"Maximum number present: "<< max_number<<endl;
return 0;
}
Although there is no need to store numbers. But it's your choice if you need it later you can use it in that program.
> what are the things I need to learn
what if the user was asked to input a hundreds of numbers
For this, you'll need to learn about arrays. I suggest you first learn about C-style arrays (int x[3]{};), and then std::array (std::array<int, 3> x{};). You also need to learn about loops.
and should display the greatest among the numbers given
Having to find the largest number in an array is very common. If you want to learn how to do so manually, the other answers here should answer your question. Otherwise, look towards the standard library algorithms std::ranges::max() (C++20) and std::max_element.
Examples
Example 1
Here's a program that uses a C-style array and a simple algorithm to get the largest number:
#include <iostream>
int main(){
// Amount of numbers user should input
constexpr int count{ 3 };
std::cout << "Enter " << count
<< " numbers to decide which is the largest:\n";
// The numbers entered by the user
double numbers[count]{}; // Declare and zero-initialize a C-style array of 3 ints
// Get each number from the user and put it in the array
for (int i{ 0 }; i < count; ++i) {
std::cin >> numbers[i];
}
// The biggest number found so far
int max{ numbers[0] }; // Initialize it with the first number
for (int i{ 1 }; i < count; ++i) { // Start at the second element (element 1)
if (numbers[i] > max) { // If the current number is larger than max...
max = numbers[i]; // ...assign it to max
}
}
std::cout << max << " is the greatest among the numbers given\n";
return 0;
}
Note:
int numbers[count]{};
This creates a C-style array called numbers which has count (3) elements. The first element's "index" is 0 and the last element's is 2. The {} initializes the values of all of the numbers to 0 (good practice).
for (int i{ 0 }; i < count; ++i)
std::cin >> numbers[i];
This loops until i isn't less than count (3) and increments i (++i) each time. It starts at 0, so it loops 3 (0 1 2) times. On each iteration, it gets a number from the console and stores it in numbers[i].
Example 2
Here's a shorter program that uses the standard library:
#include <algorithm> // ranges::max()
#include <array> // array<>
#include <iostream> // cin, cout
int main() {
// Amount of numbers user should input
constexpr int count{ 3 };
std::cout << "Enter "
<< count
<< " numbers to decide which is the largest:\n";
std::array<double, count> numbers{}; // Declare an array of 3 ints
for (int i{ 0 }; i < count; ++i) {
std::cin >> numbers[i];
}
// Return the largest number in array "numbers"
std::cout << std::ranges::max(numbers)
<< " is the greatest among the numbers given\n";
return 0;
}
Note:
std::array<int, count> numbers{};
Declares an array of count (3) ints and zero-initializes it.
std::ranges::max(numbers)
This neat function finds the largest number in numbers. It was added in C++20 -- if you're using an older compiler, you should use *std::max_element(numbers.begin(), numbers.end()). If you want to learn how the latter works, you need to learn about iterators and pointers.
Here are some good practices that your tutorial hasn't taught you yet (if it ever will):
DON'T use using namespace std. It's unsafe because it brings everything in the standard library into global scope. The standard library contains a lot of commonly used identifiers like count and list. Bringing these into global scope is dangerous because it can cause naming conflicts.
Don't use copy initialization (int x = 3). Use uniform/brace/list initialization instead (int x{ 3 }). The former sometimes makes an unnecessary copy, whereas the latter doesn't. The latter also refuses to do narrowing conversions (e.g. initializing a short with a long).
Always initialize variables (do: int x{}, don't: int x), even when it seems redundant. If you don't, then the value stored is undefined - it could be anything. Undefined behaviour is hard to debug but luckily easy to avoid.
Use \n instead of std::endl. Both do the same, except std::endl does an extra buffer flush which is slow and unnecessary. \n is shorter anyways.
DRY -- Don't Repeat Yourself. You have the string " is the greatest among the numbers given" three times in your code. You could have stored it in a std::string instead -- then it wouldn't have repeated.
Repeating code is bad, because:
It's harder to read
It's harder to maintain (you would have to modify it everywhere it's repeated)
Maintenance is more error-prone
If I were you, I'd immediately find a different tutorial/book. See this thread.
#include <stdio.h>
int main()
{
int num1, num2, num3, num4;
printf("Enter num1\n");
scanf("%d",&num1);
printf("Enter num2\n");
scanf("%d",&num2);
printf("Enter num3\n");
scanf("%d",&num3);
printf("Enter num4\n");
scanf("%d",&num4);
if(num1>num2 && num1>num3 && num1>num4){
printf("greatest number is %d",num1);
}
if(num2>num3 && num2>num1 && num2>num4){
printf("greatest number is %d",num2);
}
if(num3>num1 && num3>num2 && num3>num4){
printf("greatest number is %d",num3);
}
if(num4>num1 && num4>num2 && num4>num3){
printf("greatest number is %d",num4);
}
return 0;
}
I need some kind of error handler if I enter a string larger than the set size.
cout << "Enter long of the string" << endl;
cin >> N;
char* st = new char[N];
char* st1 = new char[N];
for (int i = 0; i < N; ++i) {
*(st1 + i) = ' ';
}
cout << "Enter string in the end put 0,without whitespace in the end." << endl;
cin.getline(st, N, '0');
First some comments.
Do not use C-Style arrays in C++ (like char data[N])
Always use std::string for strings
Never use char arrays for strings
Never ever use raw pointers for owned memory in C++
Neally never use new in C++
Avoid using pointer arithmetic with raw pointers pointing to owned memory
So, you should rethink your design. Start doing it correctly in the first place.
To answer you concrete question: If you read the documentation of the getline, then you can see that
count-1 characters have been extracted (in which case setstate(failbit) is executed).
So, the failbit will be set. You can check this with
if (std::cin.rdstate() == std::ios_base::failbit)
But as you can also read in the documentation
Extracts characters from stream until end of line or the specified delimiter delim.
So, it will not work, as you expect, It will try to read until 0 has been read. I think it will not work for you.
You also need to delete the newed memory. Otherwise, you are creating a memory hole. Look at you example again and try it:
#include <iostream>
int main() {
size_t N;
std::cout << "Enter maximum length of the string\n";
std::cin >> N;
char* st = new char[N];
char* st1 = new char[N];
for (size_t i = 0U; i < N; ++i) {
*(st1 + i) = ' ';
}
std::cout << "Enter string in the end put 0, without whitespace in the end.\n";
std::cin.getline(st, N, '0');
if (std::cin.rdstate() == std::ios_base::failbit) {
std::cin.clear();
std::cout << "\nError: Wrong string entered\n\n";
}
delete[] st;
delete[] st1;
return 0;
}
Solution for all your problems: Use std::string and std::getline
I am given a C++ programming problem: In a string I need to find wether or not there are balanced parentheses. If not, using pointers I should find position of the characters between unclosed parentheses (between second opening and nearest closing).
The problem statement is a bit confusing, I know. I think it should work somehow like that:
Input #1:
((aba)aaab)
Output:
OK.
Input #2:
(aa(a)ab
Output:
Parentheses not balanced: between characters 1 and 6.
Code below solves part of problem with the closed parentheses check and also there is a structure to keep the address of the opening parenteses. I am not sure how exactly to use pointers for that purposes, some attempts did not give any result, so I need some help here.
#include<iostream>
#include<string>
#include<stack>
using namespace std;
struct br_data{
char br_t;
char *cptr; //store the address of the opening parenthesis
};
int main (){
string input;
int addr;
br_data br;
getline(cin, input);
stack<br_data> braces;
char *a = input[0];
auto init_char = static_cast<void*>(&a); //store the address of the first character in the input string
cout << static_cast<void*>(&a) << endl; //gives the address in memory
for(auto c: input) {
if (c == '(') {
br.br_t = c;
br.cptr = &c; //storing the address of the first parenhesis
braces.push(br);
} else if (c == ')' ) {
if (braces.empty())
cout << "This line does not contain unclosed parentheses\n";
if (!braces.empty())
braces.pop();
}
}
if (!braces.empty()){
//int addr = br.cptr;
cout << "This line does not contain unclosed parentheses\n";
//int pos = (&br.cptr) - (&a); //how to calculate the position??
cout << "Position of the second opening parenthis is " << () << endl;
//cout << "Position of the nearest closing parenthis is " << -how?? (static_cast<void*>(&br.cptr)) << endl;
}
if (braces.empty()){
cout << "Parentheses are balanced in this line\n";
}
return 0;
}
When you write
br.cptr = &c; //storing the address of the first parenhesis
you're actually storing the address of a local object of char type declared earlier:
auto c: input
By the moment you exit the loop it is officially dangling.
One simplest solution would be to actually consider string's characters, not their local copies:
for(auto &c: input) {
(and, even better, change auto into char for better clarity keeping source length the same). Then you can go on and see how your solution needs to be fixed further.
(A few extra free advice: input[0] is a rvalue reference of type char so it makes no sense to assign it to a variable of type char *, and what you try to do in that line is actually written as char *a = input.c_str(); or input.data() or even &input[0], pick the best option; and br.cptr is of type pointer-to-char already, so the character's position in a string would be calculated as br.cptr - a, you need to subtract the pointers themselves, not their addresses.)
#include <iostream>
using namespace std;
int main(){
char str[]="Hello Programming";
char *ptr;
char ch;
char s;
s='n';
ptr=str;
cout<<"To be found Character"<<endl;
cin>>ch;
while(*ptr++ != '\0')
if(*ptr==ch)
s='y';
if (s=='y')
cout<<"FOUND";
else
cout<<"not found";``
return 0;
}
this script is supposed to output array values that were inputted by the user into array "store." I am trying to store all the char array values into string temp. I get the error on line 12: "[Error] invalid conversion from 'char*' to 'char' [-fpermissive]." Would appreciate any help!
Edit: so I fixed the declaration and now at least it compiles, but the answer I get on my cmd is all jumbled up. Why is this so? The cmd only correctly couts the first string but after the space, it messes up.
#include <iostream>
#include <cstdlib>
using namespace std;
void coutArray(char[], int);
int main()
{
char store[50];
cout << "enter text: " << endl;
cin >> store;
coutArray(store, 50);
system("pause");
return 0;
}
void coutArray(char store[], int max)
{
string temp = "";
int i = 0;
while (i < max)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
Using input from all answerers I finally got the fixed code:
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
void coutArray(char[], int);
int main()
{
char store[50] = {0};
cout << "enter text: " << endl;
cin.getline(store, 50);
coutArray(store, 50);
system("pause");
return 0;
}
void coutArray(char store[], int max)
{
string temp = "";
int i = 0;
while (i < max && store[i]!=0)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
Thanks everyone. i learned a lot!!!
When you get an input using "cin" your input automatically ends with 0 (NULL).
You just need to add one little piece of code to your while statement.
instead of this :
while (i < max)
use this :
while (i < max && store[i]!=0)
Now it will stop when the input string is finished and won't print any garbage existed in the array beforehand.
To show that cin does add terminating zero, i initialized the array to 46, and put a breakpoint after the cin
so I fixed the declaration and now at least it compiles, but the answer I get on my cmd is all jumbled up. Why is this so?
Not sure what you mean by jumbled up. But since you did not tell us what you typed its hard to know it looks like it worked to me:
> ./a.out
enter text:
Plop
Plop�ȏU�
Notice that since my input is only 4 characters long. This means that a lot of the characters in the array still have undefined (ie random values). This is why I am seeing junk. To get past this initialize the array to have all 0 values.
char store[50] = {0};
Even bettern use a C++ object than handles longer strings.
std::string store;
std::getline(std::cin, store);
Note: passing arrays to functions by value is not a good idea. On the other end they have decayed to pointers and thus do not act like arrays anymore (they act like pointers whose semantics are similar but not identical).
If you must pass an array pass it by reference. But I would use a C++ container and pass that by reference (it is much safer than using C constructs). Have a look at std::string
The declaration of the function is wrong. Should be void coutArray(char *, int);
Look at the Implicit Conversion rules to understand what the compiler can do and what it cannot to do for you.
The issue with your program was that you were probably entering in less characters than the maximum size of the buffer. Then when you passed the maximum size as the parameter to coutArray, you assigned unfilled slots in the char array to temp. These unfilled slots could contain anything, as you have not filled them up to that point.
Your program is still correct, but what would be better would be to use read so that the number of bytes you specify is the minimum number of bytes that can be entered:
std::cin.read(store, 50);
Even better solution would be to use std::string:
std::string store;
std::cin >> store;
// or for the entire line
std::getline(std::cin, store);
It also follows that your coutArray should be changed to:
void coutArray(std::string);
// ...
void coutArray(std::string str)
{
std::cout << str << std::endl;
}
Look at this way
template<typename T, size_t N>
void MyMethod(T (&myArray)[N])
{
//N is number of elements, myArray is the array
std::cout<<"array elements number = "<<N<<endl;
//put your code
string temp;
temp.resize(N+1);//this is for performance not to copy it each time you use += operator
int i = 0;
while (i < max)
{
temp += store[i];
i++;
}
cout << temp << endl;
}
//call it like this
char arr[] = "hello world";
MyMethod(arr);
I saw an older post on here asking how to do relatively the same thing, but their approach was different and i'm interested to know the hole in my program.
I am attempting to write a program that accepts characters into a 10 character length array. I want the program to evaluate the first array position and delete any duplicates it finds later in the array by identifying a duplicate and moving all of the values to the right of it to the left by one. The 'size' of the array is then decreased by one.
I believe the logic I used for the delete function is correct but the program only prints an 'a' for the first value and the fourth value in the array.
Any help would be greatly appreciated, here is my code:
#include <iostream>
using namespace std;
int letter_entry_print(int size, char array[10]);
int delete_repeats(int& size, char array[10]);
int final_array_print(int size, char array[10]);
int main()
{
char array[10];
int size = 10;
letter_entry_print(size,array);
delete_repeats(size,array);
final_array_print(size,array);
cout<<"\n";
system("pause");
}
int letter_entry_print(int size, char array[10])
{
int i;
for (i=0;i<size;i++)
{
cout << "Enter letter #" << i+1 << endl;
cin >> array[i];
cout << "\n";
}
cout << "\nYour array index is as follows:\n\n";
for (i=0;i<size;i++)
{
cout << array[i];
cout << " ";
}
cout <<"\n\n";
return 0;
}
int delete_repeats(int& size, char array[10])
{
int ans;
int loc;
int search;
int replace;
char target='a';
cout << "Enter 1 to delete repeats.\n\n";
cin >> ans;
if(ans==1)
{
for(loc=0;loc<size;loc++)
{
array[loc]=target;
for(search=1;search<(size-loc);search++)
{
if(target=array[loc+search])
{
for(replace=0;replace<(size-(loc+search));replace++)
{
array[loc+search+replace]=array[loc+search+replace+1];
array[size-1]=0;
size=(size-1);
}
}
}
}
}else(cout<<"\nWhy didn't you press 1?\n\n");
return 0;
}
int final_array_print(int size, char array[10])
{
cout<<"\nYour new index is as follows:\n\n";
int i;
for(i=0;i<size;i++)
{
cout<<array[i];
cout<<" ";
}
cout<<"\n";
return 0;
}
Ok, there are a few things about your code that look odd.
1) you repeat 10 all over the place to the point where there's no way you could resonably change it, but you also pass size along. Instead of making all your functions take arrays of 10 chars, consider just passing in a pointer to char, like:
int final_array_print(int size, char *array)
then you can change the size of your arrays more easily. There's no point in passing size everywhere if you're going to limit yourself forever to 10 items, and there's no good reason to pass arrays of 10 items around if you provide a size!
2) ok, so now you want to look for duplicates. Why do you overwrite the first element in your array with an 'a'?
char target='a';
...
array[loc]=target;
wouldn't you want to do it the other way around?
3) next, as #Mahesh points out, you probably want to use the comparison operator '==' rather than the assignment operator = when looking for duplicates that is:
if(target=array[loc+search])
should probably be
if(target == array[loc+search])
4) Next, dontbeafraidtousealittlewhitespacebetweenyourwordsandpunctuation.Itmakesitaloteasiertoidentifytypingmistakesandspellingerrors.
5) your loop to actually perform the replacement has incredibly complicated indices. It would be easier if you didn't start with replace = 0, but just start at replace = search + 1, try it out and perhaps you'll how much simpler all the rest of the indices become.