Numerical Integration in C

#define ADC_ENABLE ADCSRA |= (1<<ADEN)
#define ADC_DISABLE ADCSRA &= 0x7F
#define ADC_START_CONVERSION ADCSRA |= (1<<ADSC)

void adc_mega32_init(void)
{
  ADCSRA = 0x00; //switch off adc
  ADMUX = 0xC0; // adc input 0, ref = 2.56 V...
  ADCSRA = 0x86; //start
}

int adc_mega32_read(void)
{
  char i;
  int ADC_temp, ADCH_temp;
  int ADC_var = 0;

  ADC_ENABLE;
  ADC_START_CONVERSION; // dummy
  while(!(ADCSRA & 0x10));
  ADCSRA|=(1<<ADIF);

  for(i=0;i<8;i++) // 8 samples
  {
  ADC_START_CONVERSION;
  while(!(ADCSRA & 0x10)); // done???
  ADCSRA|=(1<<ADIF);

  ADC_temp = ADCL; //  ADCL register
  ADCH_temp = ADCH; //ADCH
  ADC_temp +=(ADCH_temp << 8);
  ADC_var += ADC_temp;
  }

  ADC_var = ADC_var >> 3;
  ADC_DISABLE;
  return ADC_var;
}

void main ()
{
    char buffer[15];
    int m;
    unsigned int x[30], y[30];
    
    float T = 0.003;
    adc_mega32_init();
    UART1_Init(9600);
    delay_ms(100);
    
      for(m=0; m<30; m++)
      {
        x[m] = adc_mega32_read();
        delay_ms(3);
      }
      
      for(m=0; m<30; m++)
      {
        inttostr(x[m], buffer);
        Uart1_write_text(buffer);
        Uart1_write(13);
      }
    Uart1_write(13);
    
    y[0]=200; //Initial condition
    
    for(m=1; m<30; m++)
    {
     y[m] = y[m-1]+T*x[m];
    }
    
    for(m = 0; m <30; m++)
    {
      inttostr(y[m], buffer);
      Uart1_write_text(buffer);
      Uart1_write(13);
    }
    
    while(1)
    {}
}

y[m] = y[m-1]+T*x[m];