Two variables in a ‘for’ loop in C

cfor-loop

I am writing some code where I need to use two variables in a for loop. Does the below code seem alright?

It does give me the expected result.

for (loop_1 = offset,loop_2 = (offset + 2); loop_1 >= (offset - 190),loop_2 <= (190 + offset + 2); loop_1--,loop_2++)
{
    if (  (*(uint8_t*)(in_payload + loop_1) == get_a1_byte(bitslip)) &&
         ((*(uint8_t*)(in_payload + loop_2) == get_a2_byte(bitslip)))
       )
    {
          a1_count++;
    }
}

But I am getting a compiler warning which says:

file.c:499:73: warning: left-hand operand of comma expression has no effect

What does this mean?

Best Answer

The problem is the test condition:

loop_1 >= (offset - 190),loop_2 <= (190 + offset + 2)

This does not check both parts. (Well, it does, but only the result of the second part is used.)

Change it to

(loop_1 >= (offset - 190)) && (loop_2 <= (190 + offset + 2))

if you want both conditions to be checked.

Related Solutions

Bash – How to iterate over a range of numbers defined by variables in Bash

for i in $(seq 1 $END); do echo $i; done

edit: I prefer seq over the other methods because I can actually remember it ;)

Javascript – Why is using “for…in” for array iteration a bad idea

The reason is that one construct:

var a = []; // Create a new empty array.
a[5] = 5;   // Perfectly legal JavaScript that resizes the array.

for (var i = 0; i < a.length; i++) {
    // Iterate over numeric indexes from 0 to 5, as everyone expects.
    console.log(a[i]);
}

/* Will display:
   undefined
   undefined
   undefined
   undefined
   undefined
   5
*/

can sometimes be totally different from the other:

var a = [];
a[5] = 5;
for (var x in a) {
    // Shows only the explicitly set index of "5", and ignores 0-4
    console.log(x);
}

/* Will display:
   5
*/

Also consider that JavaScript libraries might do things like this, which will affect any array you create:

// Somewhere deep in your JavaScript library...
Array.prototype.foo = 1;

// Now you have no idea what the below code will do.
var a = [1, 2, 3, 4, 5];
for (var x in a){
    // Now foo is a part of EVERY array and 
    // will show up here as a value of 'x'.
    console.log(x);
}

/* Will display:
   0
   1
   2
   3
   4
   foo
*/

Best Answer

Related Solutions

Bash – How to iterate over a range of numbers defined by variables in Bash

Javascript – Why is using “for…in” for array iteration a bad idea

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