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I'm trying to sort an array, but somehow the program doesn't output anything?
I tried writing the good old for in for sorting algorithm, doesn't work, then I tried STL, still doesn't work. Here's the code:
#include <iostream>
#include <algorithm>
using namespace std;
void in(int n, int v[]){
cin>>n;
for(int i=1; i<=n; i++){
cin>>v[i];
}
}
void sortf(int &n, int v[]){
sort(v+1, v+n+1);
}
void af(int n, int v[]){
for(int i=1; i<=n; i++){
cout<<v[i]<<" ";
}
}
int main(){
int n, v[1001];
in(n, v);
sortf(n, v);
af(n, v);
}
The variable n in main() is copied to the argument int n of the function in() and changes to the argument inside the function in() will not affect the variable n in main().
Because of that, sortf() and af() are using value of n, which is uninitialized and indeterminate.
To have functions modify caller's variables, you should use references.
#include <iostream>
#include <algorithm>
using namespace std;
void in(int& n, int v[]){ // add & to make n reference
cin>>n;
for(int i=1; i<=n; i++){
cin>>v[i];
}
}
void sortf(int &n, int v[]){
sort(v+1, v+n+1);
}
void af(int n, int v[]){
for(int i=1; i<=n; i++){
cout<<v[i]<<" ";
}
}
int main(){
int n, v[1001];
in(n, v);
sortf(n, v);
af(n, v);
}
Related
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I have added bits/stdc+.h and vector both.
Still this error is coming .
Can anyone tell me why this is happening.
#include <bits/stdc++.h>
#include<vector>
void rotate(int arr[], int n);
int main()
{
int t;
scanf("%d",&t);
while(t--)
{
int n;
scanf("%d",&n);
int a[n] , i;
for(i=0;i<n;i++)
scanf("%d",&a[i]);
rotate(a, n);
for (i = 0; i < n; i++)
printf("%d ", a[i]);
printf("\n");
}
return 0;
}
// } Driver Code Ends
//User function Template for C++
void rotate(int arr[], int n)
{
vector<int> a;
a[0] = arr[n-1];
for(int i = 0 ; i<n-1 ;i++)
{
a.insert(a.back(), arr[i]);
}
for(int j : a)
cout<<j;
}
main.cpp:30:5: error: ‘vector’ was not declared in this scope
vector<int> a;
^~~~~~
Follow these: (EDITED)
(SOLUTION TO YOUR PROBLEM) Use, using namespace std as it means if the compiler finds something that is not declared in the current scope then it will go and check std.
Don't mix c and c++ syntax. Either use printf or cout.
Also check the 1st comment on this answer, as there is something you should know about "using namespace std" and "cout/cin".
No need to work two times, you can also declare and define your function at once.
Solution (but have an error in other parts)
#include <bits/stdc++.h>
using namespace std;
void rotate(int arr[], int n)
{
vector<int> a;
a[0] = arr[n - 1];
for (int i = 0 ; i < n - 1 ; i++)
{
a.insert(a.back(), arr[i]); // ITS YOUR SYNTAX, CONSIDER TO UPDATE IT
}
for (auto &it : a)
cout << it;
}
int main()
{
int t;
cin>>t;
while (t--)
{
int n;
cin>>t;
int a[n] , i;
for (i = 0; i < n; i++)
cin>>a[i];
rotate(a, n);
for (i = 0; i < n; i++)
cout<<a[i];
cout<<"\n";
}
return 0;
}
CHECK LINE NO 9 line,
and see if it's correct or not.
a.insert(a.back(), arr[i]); WRONG
You are doing something wrong there. Check this statement
error: ‘vector’ was not declared in this scope
Solved by using namespace
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I want to binary search more than once using the same function but it's showing segmentation fault. For one input its giving correct answer but when I am giving multiple input for binary search(i.e, q>1 acc. to my code) then its showing segmentation fault.
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int binarySearch(int x[],int l, int r, long int m ){
if(r>=1){
int mid=(r-1)/2+l;
if (x[mid]==m) return mid;
if (x[mid]>m) return binarySearch(x,l,mid-1,m);
if (x[mid]<m) return binarySearch(x,mid+1,r,m);
}
return 0;
}
int main(){
int n,q;
cin>>n;
int x[n];
for(int i=0;i<n;i++){cin>>x[i];}
int t = sizeof(x) / sizeof(x[0]);
sort(x,x+t);
cin>>q;
while (q--){
long int m;
cin>>m;
cout<<binarySearch(x,0,t-1,m)<<endl;
}
return 0;
}
The condtion r>=1 should be r-l+1>=1 to check if there are some element in the range.
The initialization int mid=(r-1)/2+l; should be int mid=(r-l)/2+l; to correctly calculate the middle element.
Variable-Length Array int x[n]; is not in the standard C++. You should use heap allication int *x = new int[n]; instead. After that, n should be used for the initialization of t because the technique to obtain the number of elements in arrays won't work with pointers.
#include <iostream>
#include <algorithm>
using namespace std;
int binarySearch(int x[],int l, int r, long int m ){
if(r-l+1>=1){
int mid=(r-l)/2+l;
if (x[mid]==m) return mid;
if (x[mid]>m) return binarySearch(x,l,mid-1,m);
if (x[mid]<m) return binarySearch(x,mid+1,r,m);
}
return 0;
}
int main(){
int n,q;
cin>>n;
int *x = new int[n];
for(int i=0;i<n;i++){cin>>x[i];}
int t = n;
sort(x,x+t);
cin>>q;
while (q--){
long int m;
cin>>m;
cout<<binarySearch(x,0,t-1,m)<<endl;
}
delete[] x;
return 0;
}
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In the following program:
#include <iostream>
#include <cmath>
using namespace std;
int diagonalDifference(int x[][],int n)
{
int sum1=0,sum2=0,y;
for(int i=0;i<n;i++)
{
sum1+=x[i][i];
sum2+=x[i][n-1-i];
}
y=abs(sum1-sum2);
return y;
}
int main()
{
int n,**z;
cin>>n;
int arr[n][n];
for(int i=0;i<n;i++)
{
for(int j=0;j<n;j++)
{
cin>>arr[i][j];
}
}
z=diagonalDifference(arr,n);
cout<<x;
return 0;
}
I get a compilation error I don't understand.
error:declaration of 'x' as multidimensional array must have bounds for all dimensions except the first
Could you help me fix it?
int[][] is not a valid type:
int diagonalDifference(int x[][],int n)
You declare z as an int**:
int n,**z;
But you assign it an int:
int diagonalDifference(int x[][],int n);
z=diagonalDifference(arr,n);
And finally you print x which does not exist:
cout<<x;
As rules of thumb:
declare only one variable per line, and give it a meaningful name;
declare what possibly can as const;
Don't use C-style arrays unless you have to; prefer std::vector for instance;
don't use using namespace std;
much more you need to learn.
.
int diagonalDifference(int x**,int n) { /* .... */ }
int matrix_size = 0;
std::cin >> matrix_size;
std::vector<std::vector<int>> matrix{matrix_size, std::vector<int>{matrix_size}};
/* fill the matrix */
const int diag_diff = diagonalDifference(matrix, matrix_size);
std::cout << diag_diff << '\n';
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I am trying to write a program which prints the cubes of inserted elements of array, and then prints the sum of elements divisible by 2, and not divisible by 3.
#include <iostream>
#include <math.h>
using namespace std;
void kub(int *niz[], int n)
{
int i=0;
while(i<n)
{
*niz[i]=pow(*niz[i],3);
i++;
}
}
void unesi(int* niz[],int n)
{
int i=0;
while(i<n)
{
cin>> *niz[i];
i++;
}
}
void stampaj(int* niz[],int n)
{
int i=0;
while(i<n)
{
if ((*niz[i]%2)==0 && (*niz[i]%2)!=0)
cout<<*niz[i]<<endl;
i++;
}
}
int main()
{
int n;
cin>>n;
int niz[n];
unesi(niz,n); /* <<= here */
kub(niz,n);
stampaj(niz,n);
return 0;
}
Everything is fine, until this line of code (marked "<<= here"): "unesi(niz,n);" What am I doing wrong?
Instead of:
void unesi(int* niz[],int n)
try:
void unesi(int niz[],int n)
niz[] decays to pointer, so no need to pointer to pointer
Same for the other functions. Last note, instead of cin>> *niz[i]; just use cin>> niz[i];
In C++,
int* nix[]
is actually translated into
int** nix
at compile time. To fix this you can use either
int* nix
int nix[]
Also in the function body you would probably need to change
*nix[i]
into
nix[i]
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I have an issue with my code, I can fill the table but when I display it, it display 0 for me, here is my code
#include<iostream>
#include<vector>
using namespace std;
int n;
void lire_tab(vector<int> A);
void tri_tab(vector<int> A);
void aff_tab(vector<int> A);
int main()
{
cout<<"donnez la taille du tableau: ";
cin>>n;
vector<int> A(n);
lire_tab(A);
aff_tab (A);
tri_tab (A);
aff_tab (A);
return 0;
}
void lire_tab(vector<int> A)
{
for(int i=0;i<n;i++)
{
cout<<"A["<<i<<"]= ";
cin>>A[i];
}
cout<<"________________________"<<endl;
}
void tri_tab(vector<int> A)
{
int temp;
temp=0;
for(int i=0; i<n; i++)
{
for(int j=0; j<n; j++){
if(A[i]<A[j])
{
temp = A[i];
A[i] = A[j];
A[j] = temp;
}
}
}
}
Can you help me please, I'm really lost in this, I don't really figure out why it print 0
Your functions are using passing by value, therefore, a copy is seen within the function.
Please read about passing by reference
void lire_tab(vector<int>& A);
Instead of accepting the vector by value
void lire_tab(vector<int> A)
You want to accept the vector by reference
void lire_tab(vector<int>& A)
Otherwise you are only modifying a function-local copy of your vector, not the original vector that was passed in.