vector biginner

[Roody]

hi , i have this code about finding the max number in a vector , the output always 0 , i don't know why ..

 #include<iostream>
#include<conio.h>
#include<vector>
using namespace std;

int findmax(vector<int>);

int main()
{
	vector <int> v1(5);
	cout << " Enter 10 numbers to find the max number :\n " ;
	for(int i=0;i<v1.size();i++)
		cin>>v1[i];
	cout << " the max number is : " <<findmax(v1);

	
	getch();
	return 0;
}
int findmax(vector<int>){
	 int max=0;
	vector<int>v1;
	for(int i=0;i<v1.size();i++)
		if(max<v1[i])
			max=v1[i];

return max;
}

[Thomas1965]

The error is that you work with an empty vector in findmax.

int findmax(vector<int>)
{
  int max=0;
  vector<int>v1;

You need to pass the vector by reference from main.

[Roody]

i can't use reference , is there any other way ?

[48T7M4Gy]

i can't use reference , is there any other way ?

#include<iostream>
#include<vector>

using namespace std;

int findmax(vector<int>);

int main()
{
	vector <int> v;
	v.push_back(5);
	v.push_back(17);
	v.push_back(2);
	v.push_back(3);
	
	cout << "The max number is : " << findmax(v);
	
	return 0;
}

int findmax(vector<int> x)
{
    vector<int>::iterator it = x.begin();
    int max = *it;
    
    for (it = x.begin() ; it != x.end(); ++it)
    {
        if ( *it > max )
        max = *it;
    }
    return max;
}

The max number is : 17 
Exit code: 0 (normal program termination)

[JLBorges]

#include<iostream>
// #include<conio.h> // *** non-standard; avoid
#include <vector>
#include <limits> // *** added
// using namespace std; // also avoid

// int findmax(vector<int>);
int find_max( std::vector<int> ) ; // passed by value

int main()
{
	// vector <int> v1(5);
	std::vector<int> v1(10) ;

	// cout << " Enter 10 numbers to find the max number :\n " ;
	std::cout << "Enter " << v1.size() << " numbers to find the max number :\n" ;
	// for(int i=0;i<v1.size();i++)
		// cin>>v1[i];

	// favour writing the non-compound statements (ones without {} around it) in the same line
	for( std::size_t i = 0; i < v1.size(); ++i ) std::cin >> v1[i] ;

	std::cout << "the max number is : " << find_max(v1) << '\n' ;

	//getch(); // non-standard
	std::cin.ignore( 1000, '\n' ) ; // throw away everything in the current line in the input buffer (including the new line)
	std::cout << "press enter to end program\n" ;
	std::cin.get() ; // wait for the user to press enter

	// return 0; // implicit
}

// int findmax(vector<int>){
int find_max( std::vector<int> v1 ) // v1 is the vector passed to the function
{ // use a consistent indent style
    // int max=0;

    // we need to check if the vector is empty before we try to access any value in it
    if( v1.empty() ) return std::numeric_limits<int>::min() ; // may want to throw an error instead

    int max =  v1.front() ; // the element at the front is the one at position zero ie. v1[0]

    // vector<int>v1; // *** vector v1 is passed to the function, use that

    for( std::size_t i = 1; i < v1.size(); ++i ) if( max < v1[i] ) max = v1[i];

    return max;
}