keypad scanning programming in C

uint8_t taste = 0;

#define ta1 0b00001110   //Switch definations You can also use tamul or tadiv
#define ta2 0b00001101
#define ta3 0b00001011
#define ta4 0b00000111
#define ta5 0b00011110
#define ta6 0b00011101
#define ta7 0b00011011
#define ta8 0b00010111
#define ta9 0b00101110
#define ta10 0b00101101
#define ta11 0b00101011
#define ta12 0b00100111
#define ta13 0b00111110
#define ta14 0b00111101
#define ta15 0b00111011
#define ta16 0b00110111
//...
uint8_t readtast (void)
{
uint8_t r = 0, i = 0;
DDRB = 0b00000001;
PORTB = 0b00001110;
r = PINC & 0b00001111;
if (r<0x0F)
    {
    i=r;
    }
    
DDRB = 0b00000010;
PORTB = 0b00001101;
r = PINC & 0b00001111;
if (r<0x0F)
    {
    i=r+0x10;
    }

DDRB = 0b00000100;
PORTB = 0b00001011;
r = PINC & 0b00001111;
if (r<0x0F)
    {
    i=r + 0x20;
    }

DDRB = 0b00001000;
PORTB = 0b00000111;
r = PINC & 0b00001111;
if (r<0x0F)
    {
    i=r+0x30;
    }

if ( i == 0b00001111)
{
    i=0;
}
    
return i;            
}

void dosome (uint8_t tasi)
{
    switch (tasi)
    {
        case ta1:
        asm ("nop");
        // do something
        break;
        
        case ta2:
        asm ("nop");
        // do something other
        break;
        //...
    }
    
}
int main(void)
{
  
    DDRC = 0b00000000;
    PORTC = 0b00001111;
    DDRB = 0b00000000;
    PORTB = 0b00001111;

    //sei();
    while (1)
    {
        //asm ("nop");
        taste = readtast(); //Repeated action has to be avoid not in code yet
        dosome(taste);
        
        
        // Place your code here

    }
}