C/C++ What Is the Purpose of a Loop Variable in C++?

[ineedhelpnow]

what is the purpose of a loop variable (i)? how is it useful?

 

[alyafey22]

A loop variable defines the number of iterations the loop can go on before terminations. Usually we increment it by one after each iteraction and we set the condition dependent on it. We could use it for many purposes

1. Output information about the number of iterations

int i=0;

while(i< maxNumberOfIterations)
   printf("This is iteration number %d" , i);
   i++;
end while

As we see from the example it is very useful for debugging.

2. Accessing a sequence of information

It comes very handy when we work with arrays or other data structures

int array [] = {1 , 2 , 3 , 4};
int i=0;

while( i < array.Length)
   printf("%d  " , array[i++]);
end while

3. Determining the number of iterations for an undetermined loop

Usually we code a loop that we don't know when will it stop !

int i=0;

while(ConditionSatisfied())
   i++;
end while 

printf("The loop ran for %d iterations "  , i);

We can use that to count the number of characters in a string

int i=0; 
string word = getString();

while(word.hasNextChar())
  i++;
end while

printf("the string has %d characters ", i);

 

[ineedhelpnow]

but instead of like i >= 100 why can't you use the actual name like for example numBugs >= 100

 

[alyafey22]

Usually we use $i$ to define an iteration. This symbol also appears in mathematical problems that include sequences and series. I think it is only a convention , you can use other names if they are more descriptive. For example, we can use counter. Here is a nice thread about why using $i$.

 

[ineedhelpnow]

@zaid (Blush) uuuuh i still don't understand. is it used when there's no actual variable to be used only?

 

[alyafey22]

@zaid (Blush) uuuuh i still don't understand. is it used when there's no actual variable to be used only?

It is a variable so you can use any name you want but it is always recommended to use a conventional name (most programmers understand) or a descriptive name (describes its own purpose).