Can someone pls explain the different output in this 2 for loops c++

Question

#include <iostream>
using namespace std;

int main() {
int i;
for(i = 0; i < 4; ++i){
for(int j = 0; j < 4; ++j){
i = i + j;

cout<<i;
//0136
}

//cout<<i;
//6
}
//cout<<i;
//7
return 0;
}

Answer 1

In the given code two for loops are nested.
The outer one executes 4 time and the one inside executes its statement block :i=i+j; 4 times for each iteration of outer for loop.

One may think inner most statements will be executed 4*4 times but this isn't the case as because we are modifying counter of outer for in inner for.

Well , I think I'm confusing you here 😅😅. Let's see how it works.

first iteration of outerfor i=0;
first iteration of innerfor j=0
i=i+j=0+0=0
prints=>0

second iteration of innerfor j=1
i=i+j=0+1=1
prints=>1

third iteration of innerfor j=2
i=i+j=1+2=3
prints=>3

four iteration of innerfor j=3
i=i+j=3+3=6
prints=>6

Now! Innerfor loop breaks!🐒 why? Because j<4 evaluates to false as j=4 now.as it breaks control reaches next statements cout<<i;
prints, =>6

i++ =>increments 6 to 7
Outerfor loop checks condition.
i<4 ....false.
Next statement executed. I. E.
cout<<i;
prints=>7.