Why variable does not change after changing it within a for loop?

Question

This is my code

#include <iostream>

int main()
{
    int j = 1;
    for (int i=0, j=1; i<10; i++)
    {
        std::cout << j << std::endl;
        j++;
    }
    std::cout << j << std::endl;

    return 0;
}

This is my output:

I just want to know why the value of j does not change out

The for loop has its own local `j`. Consider what `int i = 0, j = 1` does. — sweenish, Apr 27 '21 at 14:54
You have two variables names j. One declared outside loop and one declared in the for statement. — ravenspoint, Apr 27 '21 at 14:55
`int i=0, j=1` means `int i=0; int j=1;`, not `int i=0; j=1;`. — jarmod, Apr 27 '21 at 14:57
after a bit of pushing (`-Werror -Wshadow`), gcc can report the mistake in your code as an error: https://godbolt.org/z/GT95GovEs, — 463035818_is_not_an_ai, Apr 27 '21 at 14:57

score 5 · Accepted Answer · answered Apr 27 '21 at 14:55

5

You have two variables j:

    int j = 1; // 1st "j" here
    for (int i=0, j=1; i<10; i++) // 2nd "j" here

You are modifying 2nd j in the loop and printing 1st j after the loop.

answered Apr 27 '21 at 14:55

MikeCAT

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It's quite possible OP did not intend to create a second var. In this case, they could use (the not so nice) `for (int i=(j=1,0); i<10; i++)` – Jeffrey Apr 27 '21 at 15:05
2

@Jeffrey I think it should simply be `for (int i=0; i<10; i++)` in this case because `j` is already initialized to `1` at the declaration. – MikeCAT Apr 27 '21 at 15:07
1

yeah. The mystery really is why specify `j=1` at that exact location – Jeffrey Apr 27 '21 at 15:09

Why variable does not change after changing it within a for loop?

1 Answers1