AC_setting_example, C (gcc)

AC_setting_example

//gcc 5.4.0

// Imagine an AC system that is controlled using an 8-bit number:
// The lowest two bits of the number show the fan setting: 00 is for off, 01 is for low, 10 is for medium and 11 is for high.
// The second two bits of the number show the humidity setting: 00 is for low, 01 is for medium, and 10 is for high. 11 is not an option.
// The upper 4 bits show the temperature setting. 60 degrees is represented as 0000, 61 as 0001 and so on. The highest temperature setting is 75 as 1111. 
// The following functions are written to set, update or print this AC's settings

#include  <stdio.h>

// We use enum and define so that all the setting values are in one place at the beginning of the program
// We try to avoid hard-coding actual numbers inside the code as much as possible

// For each of the below masks, all the bits are 0 except for the specific bit mentioned 
#define BIT0_MASK 1
#define BIT1_MASK (1<<1)
#define BIT2_MASK (1<<2)
#define BIT3_MASK (1<<3)
#define BIT4_MASK (1<<4)
#define BIT5_MASK (1<<5)
#define BIT6_MASK (1<<6)
#define BIT7_MASK (1<<7)
#define BIT8_MASK (1<<8)

enum FAN_SETTINGS {FAN_OFF, FAN_LOW, FAN_MED, FAN_HGH};

// The mask for the fan has 1 for the lowest two bits and 0 for the rest
#define FAN_MASK (BIT0_MASK | BIT1_MASK)

// This function prints the AC setting in this format:
// "Fan is ... Humidity is ...Temperature is ..."
void printACSetting(int ACSetting)
{
    int fanSetting = ACSetting & FAN_MASK;
    
    switch(fanSetting) 
    {
        case FAN_OFF: 
            printf("Fan is off.");
            break;
        
        case FAN_LOW: 
            printf("Fan is low.");
            break;
        
        case FAN_MED: 
            printf("Fan is medium.");
            break;
        
        case FAN_HGH:
            printf("Fan is high.");
            break;
    }
    
    // Write the rest of printing function for humididty and temperature 
    
    return;
}

// fanSetting is a number between 0 and 3
// This functions returns the new ACSetting where all is the same except for the new fanSetting
int updateFanSetting(int ACSetting, int fanSetting)
{
    
    // FAN_MASK in binary is 11. This means it has a 1 exactly where fan setting bits are
    // inverted mask will have 1 in all bits except for fan setting bits. 
    // Note that ! operation is logical operation and is not bitwise, so it cannot be used here. 
    // Instead, we use ~ which does bit-wise inversion
    int invertedFAN_MASK = ~FAN_MASK;
    printf("\n%x\n", invertedFAN_MASK);
        
    //This clears the fan setting bits
    int updatedACSetting = ACSetting & invertedFAN_MASK; 
    
    //This puts fanSetting and the rest of AC setting together
    updatedACSetting = updatedACSetting | fanSetting;
    
    return (updatedACSetting);

// We wrote the above code for maximum readability. Here is the short version of the same code
    // return( ((ACSetting & ~FAN_MASK) | fanSetting);

}

// humiditySetting is a number between 0 and 2
// This functions returns the new ACSetting where all is the same except for the new hunmiditySetting
int updateHumiditySetting(int ACSetting, int humiditySetting)
{

}

// tempSetting is a number between 60 and 75
// This functions returns the new ACSetting where all is the same except for the new tempSetting
int updatetempSetting(int ACSetting, int tempSetting)
{

}

int readFanSetting()
{
    int fanSetting;
    printf("\nEnter fan setting: \n"); 
    scanf("%d\n", &fanSetting);
   
    if (fanSetting < FAN_OFF)
        fanSetting = FAN_OFF;
    
    else if (fanSetting > FAN_HGH)
        fanSetting = FAN_HGH;
    
    return(fanSetting);
}
    
int main(void)
{
    int ACSetting = 0x46;
    
    printACSetting(ACSetting);
        
    int fanSetting = readFanSetting();
    ACSetting  = updateFanSetting(ACSetting, fanSetting); 
    printACSetting(ACSetting);
    
      
    return 0;
}


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