char str[] = "25,000";
// locate the comma
char* ptr = strchr(str,',');
// shift remaining characters left 1 place
memmove(ptr, ptr+1, strlen(ptr+1) + 1);

#include <stdio.h>
#include <string.h>
#define MAXLEN    32
 
//////////////////////////////////////////////////////
//
// function : stripCharacters
// 
// input  : character string to be modified
// output : the modified string (original is lost!!)
// return : number of chars stripped, or -1 if error
//
//////////////////////////////////////////////////////
int stripCharacters(char * user_str)
{
   char copy_str[MAXLEN], *ptr;
   const char CHARS_TO_STRIP[10] = ",$%#";
 
   //error check, make sure string is not too long
   int stringlen = strlen(user_str);
   if (stringlen > MAXLEN)
       return -1;
 
   //make copy of user string, modified version will replace it
   strncpy (copy_str,user_str,MAXLEN);
 
   //look for first instance of "strip characters"
   ptr = strtok(copy_str, CHARS_TO_STRIP);
   strcpy(user_str,ptr);
 
   //look for additional strip characters
   while(ptr)
   {
      ptr = strtok(NULL, CHARS_TO_STRIP);
      if (ptr)
         strcat(user_str,ptr);
   }
 
   //modified string is passed back in original string variable
   //return value indicates number of chars stripped, if any
   return (stringlen - strlen(user_str));
}
 
 
 
int main()
{
   char myString[32];
   int retVal;
 
   strcpy(myString,"1,234,567,890,123");
   printf("original:  %s\n",myString);
   retVal = stripCharacters(myString);
   printf("modified:  %s   (stripped %i)\n\n",myString,retVal);
 
   strcpy(myString,"$5,299.99");
   printf("original:  %s\n",myString);
   retVal = stripCharacters(myString);
   printf("modified:  %s   (stripped %i)\n\n",myString,retVal);
 
   strcpy(myString,"0.039%");
   printf("original:  %s\n",myString);
   retVal = stripCharacters(myString);
   printf("modified:  %s   (stripped %i)\n\n",myString,retVal);
 
   strcpy(myString,"#103");
   printf("original:  %s\n",myString);
   retVal = stripCharacters(myString);
   printf("modified:  %s   (stripped %i)\n\n",myString,retVal);
 
   strcpy(myString,"999888777");
   printf("original:  %s\n",myString);
   retVal = stripCharacters(myString);
   printf("modified:  %s   (stripped %i)\n\n",myString,retVal);
 
   strcpy(myString,"123,456,789,012,345,678,901,234,567,890");
   printf("original:  %s\n",myString);
   retVal = stripCharacters(myString);
   printf("modified:  %s   (stripped %i)\n\n",myString,retVal);
 
 
   return 0;
}