Doubt in map container in c++

map<char,int> m
for(auto itr:m) {

the map contains {<‘a’,3> ans <‘b’,1>} as element.
when i run this program the loop runs 3 times but when i dont erase elemt from map it runs 2 time can anyone explain me this behaviour?

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actually it is itr.first instead of itr->first

and m[itr->first]–-;

When you use auto : it.first or it.second
When you use iterator : it->first and it->second

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You are modifying the map while iterating the container. The interators get invalidated, and its undefined behaviour.

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