My implementation of an O(n) algorithm that removes characters from a string.

remove.c

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


int main( int argc, char* argv[] ) {

  if( argc < 3 ) {
    printf( "Usage: repl <word> <char to replace>\n" );
    return 1;
  }

  char* s = (char*)malloc( strlen( argv[1] ) + 1 ) ;
  strcpy( s, argv[1] );
  const char r = argv[2][0];
  
  int i = 0;
  int j = 0;

  int k = strlen( s );

  while( 1 ) {

    if( s[i] == r  ) {
      j = j <= i ? i + 1 : j;      
      while( j < k  ) {
        if( s[j] != r  ) {
	  s[i] = s[j];
	  s[j] = r;
	  break;	  
	}

	j++;	

      }      
    } 

    if( j >= k ) break;

    i++;    
  }
  
  s[i] = 0;
  
  printf( "%s\n", s );

  free( s );
  return 0;

}