C++ STL algorithm, lower_bound() program example

Compiler: Visual C++ Express Edition 2005

Compiled on Platform: Windows XP Pro SP2

Header file: Standard

Additional project setting: Set project to be compiled as C++

Project -> your_project_name Properties -> Configuration Properties -> C/C++ -> Advanced -> Compiled As: Compiled as C++ Code (/TP)

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To do: Using the  C++ lower_bound() to search the position of the first element in an ordered range that has a value less than or equivalent to a specified value, where the ordering criterion may be specified by a binary predicate in C++ programming

To show: How to use the C++ algorithm, lower_bound() to search the position of the first element in an ordered range that has a value less than or equivalent to a specified value, where the ordering criterion may be specified by a binary predicate in C++ programming

// C++ STL algorithm, lower_bound()

#include <vector>

#include <algorithm>

// for greater<int>()

#include <functional>

#include <iostream>

using namespace std;

// return whether modulus of elem1 is less than modulus of elem2

bool mod_lesser(int elem1, int elem2)

{

if(elem1 < 0)

elem1 = - elem1;

if(elem2 < 0)

elem2 = - elem2;

return (elem1 < elem2);

}

int main(void)

{

// container

vector <int> vec1;

//iterators

vector <int>::iterator Iter1, Result1;

int i, j;

// constructing vectors vec1a & vec1b with default less than ordering

//

// pushing data

for(i = -3; i <= 6; i++)

vec1.push_back(i);

for(j =-5; j <= 2; j++)

vec1.push_back(j);

// some operations

cout<<"Operation: sort(vec1.begin(), vec1.end())"<<endl;

sort(vec1.begin(), vec1.end());

cout<<"vec1 vector data with range sorted by the binary predicate less than is: ";

for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

cout<<*Iter1<<" ";

cout<<endl;

// constructing vectors vec2 with range sorted by greater

//

// container

vector <int> vec2(vec1);

// iterators

vector <int>::iterator Iter2, Result2;

cout<<"\nOperation: sort(vec2.begin(), vec2.end(), greater<int>())"<<endl;

sort(vec2.begin(), vec2.end(), greater<int>());

cout<<"vec2 vector data with range sorted by the binary predicate greater is: ";

for(Iter2 = vec2.begin(); Iter2 != vec2.end(); Iter2++)

cout<<*Iter2<<" ";

cout<<endl;

// constructing vectors vec3 with range sorted by mod_lesser()

//

// container

vector <int> vec3(vec1);

// iterators

vector <int>::iterator Iter3, Result3;

cout<<"\nOperation: sort(vec3.begin(), vec3.end(), mod_lesser)"<<endl;

sort(vec3.begin(), vec3.end(), mod_lesser);

cout<<"vec3 vector data with range sorted by the binary predicate mod_lesser is: ";

for(Iter3 = vec3.begin(); Iter3 != vec3.end(); Iter3++)

cout<<*Iter3<<" ";

cout<<endl;

// lower_bound of 5 in vec1 with default binary predicate less <int>()

cout<<"\nOperation: lower_bound(vec1.begin(), vec1.end(), 5)"<<endl;

Result1 = lower_bound(vec1.begin(), vec1.end(), 5);

cout<<"The lower_bound in vec2 vector for the element with a value of 5 is: "<<*Result1<<endl;

// lower_bound of 5 in vec2 with the binary predicate greater<int>()

Result2 = lower_bound(vec2.begin(), vec2.end(), 5, greater<int>());

cout<<"The lower_bound in vec2 vector for the element with a value of 5 is: "<<*Result2<<endl;

// lower_bound of 5 in vec3 with the binary predicate mod_lesser

cout<<"\nOperation: lower_bound(vec3.begin(), vec3.end(), 5, mod_lesser)"<<endl;

Result3 = lower_bound(vec3.begin(), vec3.end(), 5, mod_lesser);

cout<<"The lower_bound in vec3 vector for the element with a value of 5 is: "<<*Result3<<endl;

return 0;

}

Output examples:

Operation: sort(vec1.begin(), vec1.end())

vec1 vector data with range sorted by the binary predicate less than is: -5 -4 -3 -3 -2 -2 -1 -1 0 0 1 1 2 2 3 4 5 6

Operation: sort(vec2.begin(), vec2.end(), greater<int>())

vec2 vector data with range sorted by the binary predicate greater is: 6 5 4 3 2 2 1 1 0 0 -1 -1 -2 -2 -3 -3 -4 -5

Operation: sort(vec3.begin(), vec3.end(), mod_lesser)

vec3 vector data with range sorted by the binary predicate mod_lesser is: 0 0 -1 -1 1 1 -2 -2 2 2 -3 -3 3 -4 4 -5 5 6

Operation: lower_bound(vec1.begin(), vec1.end(), 5)

The lower_bound in vec2 vector for the element with a value of 5 is: 5

The lower_bound in vec2 vector for the element with a value of 5 is: 5

Operation: lower_bound(vec3.begin(), vec3.end(), 5, mod_lesser)

The lower_bound in vec3 vector for the element with a value of 5 is: -5

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