CODEWITHSUNDEEP
c++for-loopif-statementuntil-loop
Alih3d
Alih3d

Reputation: 45

comparing two variables in c++

learning c++ and I'm sure I'm overlooking something obvious but I'm not sure why I dont get a message that i == j even though after the 3rd iteration the numbers are the same ?

This is the output:

8 is not equal to 12

9 is not equal to 11

appreciate any hints!

#include<iostream>

int main(){

   int i=8;
   int j=12; 

   for (i,j; i!=j; ++i, --j)
   {    
   if (i == j) 
        {     
         std::cout << "i = j" << "\n";   // this part doesnt work
         break;
        }
   else 

        std::cout << i <<" is not equal to " << j <<"\n"; 

   }
}

Upvotes: 0

Views: 948

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

The loop is executed only when i is not equal to j due to the condition

for (i,j; i!=j; ++i, --j)
          ^^^^

When i is equal to j the body of the loop does not get the control because the condition evaluates to false.

You should change the condition in the loop. Also the break statement is redundant.

Here is a demonstrative program.

#include <iostream>

int main()
{
    for ( int i = 8, j = 12;  not ( j < i ); ++i, --j )
    {    
        if ( i == j ) 
        {     
            std::cout << "i = j" << "\n";
        }
        else 
        {
            std::cout << i <<" is not equal to " << j <<"\n"; 
        }
    }       
}

Its output is

8 is not equal to 12
9 is not equal to 11
i = j

Pay attention to that in any case in general you may not use the condition i != j in the loop because when this range contains an even number of values when you can get an infinite loop. For example consider the case when i is equal to 10 and j is equal to 11. In this case after the first iteration of the loop i will be equal to 11 and j will be equal to 10 and again i != j.:)

Upvotes: 2

Alex
Alex

Reputation: 482

That's because your loops stops when i is equal to j, before ever printing it out. And since you break out of your loop when i is supposed equal to j, you can rewrite it like this:

    for (int i = 8, j = 12; i != j; ++i, --j)
        std::cout << i << " is not equal to " << j << "\n";

    std::cout << "i = j\n";

Upvotes: 0

Rohan Bari
Rohan Bari

Reputation: 7726

You could have used for (; i <= j; ++i, --j).

The following is modified version of your code, just changed from != to <=:

#include <iostream>

int main()
{

    int i = 8;
    int j = 12;

    for (; i <= j; ++i, --j)
    {
        if (i == j)
        {
            std::cout << "i = j" << std::endl;
        }
        else
            std::cout << i << " is not equal to " << j << "\n";
    }

    return 0;
}

Output:

8 is not equal to 12
9 is not equal to 11
i = j

Upvotes: 1

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