Fatal error: SPI.h

I am using the following example code from adafruit for their TFTs. And while compiling, i get this error and cannot solve it.

/**************************************************************************
  This is a library for several Adafruit displays based on ST77* drivers.

  Works with the Adafruit 1.8" TFT Breakout w/SD card
    ----> http://www.adafruit.com/products/358
  The 1.8" TFT shield
    ----> https://www.adafruit.com/product/802
  The 1.44" TFT breakout
    ----> https://www.adafruit.com/product/2088
  as well as Adafruit raw 1.8" TFT display
    ----> http://www.adafruit.com/products/618

  Check out the links above for our tutorials and wiring diagrams.
  These displays use SPI to communicate, 4 or 5 pins are required to
  interface (RST is optional).

  Adafruit invests time and resources providing this open source code,
  please support Adafruit and open-source hardware by purchasing
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.
  MIT license, all text above must be included in any redistribution
 **************************************************************************/

#include <Adafruit_GFX.h>    // Core graphics library
#include <Adafruit_ST7735.h> // Hardware-specific library for ST7735
#include <Adafruit_ST7789.h> // Hardware-specific library for ST7789
#include <SPI.h>

#ifdef ADAFRUIT_HALLOWING
  #define TFT_CS        39 // Hallowing display control pins: chip select
  #define TFT_RST       37 // Display reset
  #define TFT_DC        38 // Display data/command select
  #define TFT_BACKLIGHT  7 // Display backlight pin
#else
  // For the breakout board, you can use any 2 or 3 pins.
  // These pins will also work for the 1.8" TFT shield.
  #define TFT_CS        10
  #define TFT_RST        9 // Or set to -1 and connect to Arduino RESET pin
  #define TFT_DC         8
#endif

// OPTION 1 (recommended) is to use the HARDWARE SPI pins, which are unique
// to each board and not reassignable. For Arduino Uno: MOSI = pin 11 and
// SCLK = pin 13. This is the fastest mode of operation and is required if
// using the breakout board's microSD card.

// For 1.44" and 1.8" TFT with ST7735 (including HalloWing) use:
Adafruit_ST7735 tft = Adafruit_ST7735(TFT_CS, TFT_DC, TFT_RST);

// For 1.54" TFT with ST7789:
//Adafruit_ST7789 tft = Adafruit_ST7789(TFT_CS, TFT_DC, TFT_RST);

// OPTION 2 lets you interface the display using ANY TWO or THREE PINS,
// tradeoff being that performance is not as fast as hardware SPI above.
//#define TFT_MOSI 11  // Data out
//#define TFT_SCLK 13  // Clock out
//Adafruit_ST7735 tft = Adafruit_ST7735(TFT_CS, TFT_DC, TFT_MOSI, TFT_SCLK, TFT_RST);

float p = 3.1415926;
Arduino: 1.6.9 (Windows 8.1), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"

In file included from C:\Users\Ammar.Surti\Documents\Arduino\libraries\Adafruit_ST7735_and_ST7789_Library/Adafruit_ST77xx.h:31:0,

                 from C:\Users\Ammar.Surti\Documents\Arduino\libraries\Adafruit_ST7735_and_ST7789_Library/Adafruit_ST7735.h:4,

                 from C:\Users\Ammar.Surti\Documents\Arduino\libraries\Adafruit_ST7735_and_ST7789_Library\examples\graphicstest\graphicstest.ino:26:

C:\Users\Ammar.Surti\Documents\Arduino\libraries\Adafruit_GFX_Library/Adafruit_SPITFT.h:12:17: fatal error: SPI.h: No such file or directory

compilation terminated.

exit status 1
Error compiling for board Arduino/Genuino Mega or Mega 2560.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.
#include <SPI.h>

results in the error because this file is not found where the compiler is looking for it to include it.

Under the Arduino IDE's Sketch > Include Library menu, do you see "SPI" listed?