Remove all the vowels from a given string using pointers concept

#include<stdio.h>#include<stdlib.h>#include<string.h>#define TRUE 1#define FALSE 0 int check_vowel(char); main(){   char string[100], *temp, *pointer, ch, *start;    printf("Enter a string\n");   gets(string);    temp = string;   pointer = (char*)malloc(100);   if( pointer == NULL )   {      printf("Unable to allocate memory.\n");      exit(EXIT_FAILURE);   }    start = pointer;    while(*temp)   {      ch = *temp;       if ( !check_vowel(ch) )      {         *pointer = ch;         pointer++;      }      temp++;   }   *pointer = '\0';    pointer = start;   strcpy(string, pointer); /* If you wish to convert original string */   free(pointer);    printf("String after removing vowel is \"%s\"\n", string);    return 0;} int check_vowel(char a){   if ( a >= 'A' && a <= 'Z' )      a = a + 'a' - 'A';    if ( a == 'a' || a == 'e' || a == 'i' || a == 'o' || a == 'u')      return TRUE;    return FALSE;}