C program to delete all vowels from a sentence

Write a C program to delete all vowels from a string.

  #include <stdio.h>
  #include <string.h>

  int main() {
        int i = 0, j = 0, k, flag;
        char sentence[256], output[256];

        /* vowels in lowercase and uppercase */
        char vowel[10] = {'a', 'e', 'i', 'o', 'u',
                          'A', 'E', 'I', 'O', 'U'};


        /* get the input sentence from the user */
        printf("Enter your input sentence:");
        fgets(sentence, 256, stdin);
        sentence[strlen(sentence) - 1] = '\0';

        /* copy characters other than vowels to output array */
        while (sentence[i] != '\0') {
                flag = 0;
                for (k = 0; k < 10; k++) {
                        if (vowel[k] == sentence[i]) {
                                flag = 1;
                                break;
                        }
                }
                if (!flag) {
                        output[j++] = sentence[i];
                }

                i++;
        }

        output[j] = '\0';

        /* copy the contents of output to sentence */

        strcpy(sentence, output);

        /* print the result */

        printf("After deleting all vowels: %s\n", sentence);

        return 0;

  }

  Output:

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your input sentence:Expenditures Allowances
  After deleting all vowels: xpndtrs llwncs