how to initialize char and int in keil 5

This has honestly got to be the most brain damaged code I've seen in a long while. I'm not as confused as I am distressed with the logic.

When you do sizeof() of buffer thats 8 bytes long it is never going to return 4, even for very small values of 8.

You can't compare a 4 character string 6 bytes at a time. It will never match.

You can't blindly write multiple character to the TDR register.

Why do you call the IRQ Handler in the loop? What does the code in the IRQ Handler look like or do?

Perhaps try something simpler that is within your grasp, like reading characters and echoing them back, or changing the case.

This has honestly got to be the most brain damaged code I've seen in a long while. I'm not as confused as I am distressed with the logic.

When you do sizeof() of buffer thats 8 bytes long it is never going to return 4, even for very small values of 8.

You can't compare a 4 character string 6 bytes at a time. It will never match.

You can't blindly write multiple character to the TDR register.

Why do you call the IRQ Handler in the loop? What does the code in the IRQ Handler look like or do?

Perhaps try something simpler that is within your grasp, like reading characters and echoing them back, or changing the case.

This is i am using new code but output will not come.how to solve this problem.

/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "string.h"
#include "stdio.h"
#include "stm32l0xx.h"

/* USER CODE BEGIN Includes */
char rx_buffer[8] ="";
char MSG[]="skit";
int n;
/* USER CODE END Includes */

/* Private variables ---------------------------------------------------------*/

/* USER CODE BEGIN PV */
/* Private variables ---------------------------------------------------------*/
//UART_HandleTypeDef huart2;
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
static void LL_Init(void);
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);
static void MX_I2C1_Init(void);
/* USER CODE END 0 */

int main(void)
{

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration----------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  LL_Init();


  /* Configure the system clock */
  SystemClock_Config();

  MX_GPIO_Init();
  MX_USART2_UART_Init();
  MX_I2C1_Init();

        LL_USART_ReceiveData8(USART2);
        LL_USART_EnableRxTimeout(USART2);

  while (1)
  {

                n=strcmp(rx_buffer, MSG);
                        if( n== 0 )
                        {

                                LL_USART_TransmitData8(USART2, ('c'));


                                rx_buffer[0x00]=0x00;

                        }

                        else if(n>4)

                             {

                                LL_USART_TransmitData8(USART2, ('l'));
                                rx_buffer[0x00]=0x00;

                             }
                         else
                       {
                        LL_USART_TransmitData8(USART2, ('s'));


               }
                  }
                }

Still a lot of critical code that simply isn't been shown, despite being asked.

Perhaps try something simple within your grasp, without interrupts or strings

/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "string.h"
#include "stdio.h"
#include "stm32l0xx.h"

/* Private function prototypes -----------------------------------------------*/
static void LL_Init(void);
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);
/* USER CODE END 0 */

void putstring(char *s)
{
  while(*s)
  {
    /* Wait for TXE flag to be raised */
    while (!LL_USART_IsActiveFlag_TXE(USART2));

    /* Write character in Transmit Data register.
       TXE flag is cleared by writing data in TDR register */
    LL_USART_TransmitData8(USART2, *s++);
  }
}

int main(void)
{
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  LL_Init();

  /* Configure the system clock */
  SystemClock_Config();

  MX_GPIO_Init();
  MX_USART2_UART_Init(); // code not shown, don't enable interrupts

  putstring("Hello World!\n");

  while(1)
  {
    if (LL_USART_IsActiveFlag_RXNE(USART2)) /* character ready */
    {
      uint8_t ch = LL_USART_ReceiveData8(USART2); /* read it */

      /* Wait for TXE flag to be raised */
      while (!LL_USART_IsActiveFlag_TXE(USART2));

      /* Write character in Transmit Data register.
         TXE flag is cleared by writing data in TDR register */
      LL_USART_TransmitData8(USART2, ch);
    }

    if (LL_USART_IsActiveFlag_NE(USART2)
      LL_USART_ClearFlag_NE(USART2);

    if (LL_USART_IsActiveFlag_FE(USART2)
      LL_USART_ClearFlag_FE(USART2);

    if (LL_USART_IsActiveFlag_PE(USART2)
      LL_USART_ClearFlag_PE(USART2);
  }
}

If you're going to cross post, then be sure to:

1. In your new post, give a link to this thread - so that people can see what's already been said & done.

2. In this post, give a link to your new post.