STM32F4 USART receiving sting

I started 2 days ago working on STM32f4 discovery board, and i have basic background in C programming.

#include ''stm32f4xx.h''
#include ''stm32f4xx_usart.h''
#include ''stm32f4xx_rcc.h''
#include ''stm32f4xx_gpio.h''
#include ''misc.h''
void Delay(__IO uint32_t nCount)
{
while(nCount--)
{
}
}
void setup_Pheriph()
{
GPIO_InitTypeDef GPIO_InitStruct;
USART_InitTypeDef USART_InitStruct;
NVIC_InitTypeDef NVIC_InitStruct;
//ENABLE PERIPH CLOCK FOR USART2
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);
//ENABLE GPIOA CLOCK
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
//ENABLE GPIOD CLOCK
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
//SETUP GPIOA PINS FOR Tx AND Rx
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_3;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF; //SINCE WE HAVE USED ALTERNATIVE FUNCTION WE SHOULD ASIGN IT DOWN
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_25MHz;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP; //PULL UP RESISTORS
GPIO_Init(GPIOA, &GPIO_InitStruct);
//SETUP GPIOD PINS FOR BLINKING LED
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_13 |GPIO_Pin_12;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_25MHz;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOD, &GPIO_InitStruct);
//SETTING UP AF FOR UARTS2
GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_USART2); //WE SET PIN2 AND 3 AS AF FOR UART2
GPIO_PinAFConfig(GPIOA, GPIO_PinSource3, GPIO_AF_USART2);
//SETUP USART CONFIG
USART_InitStruct.USART_BaudRate = 9600;
USART_InitStruct.USART_WordLength = USART_WordLength_8b;
USART_InitStruct.USART_StopBits = USART_StopBits_1;
USART_InitStruct.USART_Parity = USART_Parity_No;
USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
USART_InitStruct.USART_Mode = USART_Mode_Tx | USART_Mode_Rx; //WE SETUP USART FOR Rx AND Tx
USART_Init(USART2, &USART_InitStruct);
USART_ITConfig(USART2, USART_IT_RXNE, ENABLE); //SETUP INTERRUPT REQUEST FOR USART FOR ONLY RECEIVE
//SETTING UP INTERRUPT REQUEST NVIC
NVIC_InitStruct.NVIC_IRQChannel = USART2_IRQn; //CHANNEL IS THE INTERRUPT NAME I WANT TO CONFIGURE
NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE; //ENABLE USART GLOBALLY
NVIC_Init(&NVIC_InitStruct);
//ENABLE USART2 PERIPHERAL
USART_Cmd(USART2, ENABLE);
}
void USART_send_char(USART_TypeDef *USARTx, char c)
{
while(!USART_GetITStatus(USARTx,USART_FLAG_TXE));
USART_SendData(USARTx, c);
}
void USART_send_string(USART_TypeDef *USARTx, volatile char *str) //WE PASS ANY USART AND STRING
{
while(*str)
{
/*while(!(USARTx->SR & 0x00000040)); //P.993 SR-> STATUS REGISTER, 0X040 -> TC FLAG
//LOOP TILL TC FLAG = 1, WHICH MEANS DATA IS TRANSFERED
//ANOTHER WAY IS LIKE THIS*/
while(!USART_GetFlagStatus(USARTx, USART_FLAG_TC )); //STAY HERE WHILE THIS FLAG IS ZERO
USART_SendData(USARTx, *str);
*str++;
}
}
uint16_t USART_receive_char(USART_TypeDef *USARTx)
{
//WAIT UNTIL CHAR IS RECEIVED
while(!USART_GetFlagStatus(USARTx, USART_FLAG_RXNE));
//READ RECEIVED CHAR
return USART_ReceiveData(USARTx);
}
uint16_t* USART_receive_string(USART_TypeDef *USARTx)
{
uint16_t string[20],x;
static int cnt = 0;
x=USART_receive_char(USARTx);
while(x!='\n' || x!='\r')
{
//STORE THE RECEIVED CHAR INTO ARRARY
string[cnt++]=x;
}
string[cnt]='\0';
return string;
}
int main(void)
{
setup_Pheriph();
USART_send_string(USART2, ''Welcome Rabah!\r\n'');
while(1)
{
}
}
uint16_t rec_char;
uint16_t *rec_string;
void USART2_IRQHandler()
{
/*rec_char = USART_receive_char(USART2);
if(rec_char == 'o')
GPIO_WriteBit(GPIOD, GPIO_Pin_13, Bit_SET);
if(rec_char == 'f')
GPIO_WriteBit(GPIOD, GPIO_Pin_13, Bit_RESET);*/
if(rec_string == ''red'')
{
GPIO_WriteBit(GPIOD, GPIO_Pin_13, Bit_SET);
}
else
{
USART_send_string(USART2,rec_string);
}
}