Remove Vowels in String

/*
Write a program in C for remove vowels in string
*/

#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;
}