# map::operator[] in C++ STL Program

C++Server Side ProgrammingProgramming

In this article we will be discussing the working, syntax and example of map equal ‘[]’ operator in C++ STL.

## What is a Map in C++ STL?

Maps are the associative container, which facilitates to store the elements formed by a combination of key value and mapped value in a specific order. In a map container the data is internally always sorted with the help of its associated keys. The values in the map container are accessed by its unique keys.

## What is a map equal to ‘[]’ operator?

map::operator[] is a reference operator. This operator is used to access the element in the container by its key.

If there is no key matching in the container, then the operator inserts a new element with that key and returns the reference of the mapped value. This operator works the same as the map::at(), the only difference is that at() throws an exception when the key is not present in the map container.

## Syntax

Map_name[key& k];

## Parameter

There is only 1 parameter i.e. the key k which we want to reference in the container.

## Return value

This operator returns the value associated to the key k.

Input

map<char, int> newmap;
newmap.insert({1, 20});
newmap.insert({2, 30});
newmap[1];

## Output

20

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
int main(){
map<int, int> TP_1;
map<int, int> TP_2;
TP_1[1] = 10;
TP_1[2] = 20;
TP_1[3] = 30;
TP_1[4] = 40;
cout<<"Element at TP[3] is : "<<TP_1[3];
return 0;
}

## Output

If we run the above code it will generate the following output −

Element at TP[3] is : 30

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
int main(){
map<int, int> TP_1;
map<int, int> TP_2;
TP_1[1] = 10;
TP_1[2] = 20;
TP_1[3] = 30;
TP_1[4] = 40;
cout<<"Element at TP[3] is : "<<TP_1[3];
if(TP_1[5]==0){
cout<<"\nElement at TP[5] doesn't exist";
}
else{
cout<<"Element at TP[5] is : "<<TP_1[5];
}
return 0;
}

## Output

If we run the above code it will generate the following output −

Element at TP[3] is : 30
Element at TP[5] doesn't exist
Published on 14-Aug-2020 11:52:09