Serialized Data Buffer

Code

#include <stdio.h>
#include <stdint.h>

enum {
    PKT_START_IDX    = 0,
    PKT_COMMAND_IDX  = 1,
    PKT_VALUE_IDX    = 2,   // bytes 2..3
    PKT_STATUS_IDX   = 4,
    PKT_CHECKSUM_IDX = 5,   // bytes 5..8
    PKT_END_IDX      = 9,
};

#define PKT_START_BYTE  ((uint8_t)0xA5)
#define PKT_END_BYTE    ((uint8_t)0x5A)

static void write_u16_le(uint8_t *dst, uint16_t value)
{
    for (int i = 0; i < 2u; i++)
    {
        dst[i] = (uint8_t)((value >> (i * 8)) & 0xFFu);
    }
}

static void write_u32_le(uint8_t *dst, uint32_t value)
{
    for (int i = 0; i < 4u; i++)
    {
        dst[i] = (uint8_t)((value >> (i * 8)) & 0xFFu);
    }
}

void build_packet(uint8_t command, uint16_t value, uint8_t status, uint32_t checksum) {
    uint8_t buffer[10];
    // Your logic to fill buffer
    buffer[PKT_START_IDX] = PKT_START_BYTE;
    buffer[PKT_COMMAND_IDX] = command;
    write_u16_le(&buffer[PKT_VALUE_IDX], value);
    buffer[PKT_STATUS_IDX]  = status;
    write_u32_le(&buffer[PKT_CHECKSUM_IDX], checksum);
    buffer[PKT_END_IDX]     = PKT_END_BYTE; 

    // Then print buffer
    for(int i = 0; i < 10; i++)
    {
        printf("%d ", buffer[i]);
    }
}

int main() {
    uint8_t cmd, status;
    uint16_t val;
    uint32_t crc;

    scanf("%hhu %hu %hhu %u", &cmd, &val, &status, &crc);
    build_packet(cmd, val, status, crc);
    return 0;
}

Solving Approach