CODEWITHSUNDEEP
cwhile-loopincrement
leykan
leykan

Reputation: 389

incrementation in while false result

I am working on a project where I must creat a matrice and initialize it. So this is what I have done to init the matrice :

int     levenshtein(char *string1, char *string2)
{
  int32_t       firstWord = strlen(string1);
  int32_t       secondWord = strlen(string2);
  int32_t       matrice[MAXWORD][MAXWORD]; //MAXWORD = 155
  int32_t       i = 0;
  int32_t       j = 0;

  while (i++ < MAXWORD)
    {
      matrice[i][0] = i;
      matrice[0][i] = i;
    }
}

So when I print the matrice I should get in matrice[0][0] = 0, matrice[1][0] = 1 etc

But when I print the matrice everything will be good exepte that matrice[1][0] it is equal to MAXWORD.

But if increment like this it while work perfectly 

while (i < MAXWORD)
  {
    matrice[i][0] = i;
    matrice[0][i] = i;
    i++
  }

Why the while (i++ < MAXWORD) will change the result of matrice[1][0] (and only matrice[1][0]) after exiting the while ?

Upvotes: 2

Views: 65

Answers (2)

Barmar
Barmar

Reputation: 781593

WHen you do the increment in the while() statement, you're adding 1 to i before you enter the body of the loop. So on the first iteration, the value of i will be 1, not 0. That's why you never initializematrice[0][0].

Moving the increment to the end of the loop means you enter it with the current value. So the first time through the loop i will be 0, not 1.

A better way to loop through a range of values is with for, not while:

for (i = 0; i < MAXWORD; i++) {
    matrice[i][0] = i;
    matrice[0][i] = i;
}

Upvotes: 1

xcervilla
xcervilla

Reputation: 76

It is because of the postincrement operator, first reads the value of your variable, and increments it by one after reading the value so in your code, the i variable will be < than MAXWORD when you do the comparison in the while, and will be equal to MAXWORD when enters the while body.

Hope that this will help you.

Upvotes: 0

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