Why is the identifier not defined?

Question

C++ / C#

Wrote a function in C? which looks for numbers in a string and then, when it hits a letter, looks for the largest letter of the resulting number, invalidates the variable that held the number, and looks for a new one in the same string. But when I run it, I get the error "w: undeclared identifier". I can't figure out what the problem is.
Function:

int funcc(char a[]) {
  int length = strlen(a);
  printf("length = %d\n", length);
  char num[255];
  for (int i = 0; i < length; i++)
  {
    if (a[i] == '0') {
      num[i] = a[i];
    }
    if (a[i] == '1') {
      num[i] = a[i];
    }
    if (a[i] == '2') {
      num[i] = a[i];
    }
    if (a[i] == '3') {
      num[i] = a[i];
    }
    if (a[i] == '4') {
      num[i] = a[i];
    }
    if (a[i] == '5') {
      num[i] = a[i];
    }
    if (a[i] == '6') {
      num[i] = a[i];
    }
    if (a[i] == '7') {
      num[i] = a[i];
    }
    if (a[i] == '8') {
      num[i] = a[i];
    }
    if (a[i] == '9') {
      num[i] = a[i];
    }
    else {
      if (w != 0) {
        int a = 0;
        while (w > 0) {
          int b = w / 10;
          if (b > a) {
            a = b;
          }
          w /= 10;
        }
      }
      continue;
    }
    int w = atoi(num);
  }
}

Answer 1

The variable w is defined later than it is used.