Need Help for STM32

Hi I am Renjith.
I am very new to keil IDE and also STM32f4 Discovery.
While doing a GPIO project, i have got output through register configuration.
The same project was done using stm32 standard gpio library, its showing linking error, I have tried my level best but could not rectify, so kindly please help....

#include "stm32f4xx.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_gpio.h"

GPIO_InitTypeDef GPIO_InitDef;

int main(void)
{
        RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);


        GPIO_InitDef.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_14;
        GPIO_InitDef.GPIO_Mode = GPIO_Mode_OUT;
        GPIO_InitDef.GPIO_OType = GPIO_OType_PP;
        GPIO_InitDef.GPIO_PuPd = GPIO_PuPd_NOPULL;
        GPIO_InitDef.GPIO_Speed = GPIO_Speed_100MHz;
        //Initialize pins
        GPIO_Init(GPIOD, &GPIO_InitDef);

        //volatile int i;
    while (1)
                {
                        GPIO_SetBits(GPIOD, GPIO_Pin_13 | GPIO_Pin_14);
    }
}

And i got this error
Rebuild target 'main'
compiling Main.c...
assembling startup_stm32f407xx.s...
compiling system_stm32f4xx.c...
linking...
.\Objects\main.axf: Error: L6218E: Undefined symbol GPIO_Init (referred from main.o).
.\Objects\main.axf: Error: L6218E: Undefined symbol GPIO_SetBits (referred from main.o).
.\Objects\main.axf: Error: L6218E: Undefined symbol RCC_AHB1PeriphClockCmd (referred from main.o).
Not enough information to list image symbols.
Finished: 1 information, 0 warning and 3 error messages.
".\Objects\main.axf" - 3 Error(s), 0 Warning(s).
Target not created.
Build Time Elapsed: 00:00:04

Please help me to find a solution.