Help with code, trying to learn c language

[HappyC4mper]

There is a countBits function which i do not know how to complete.
Can someone show me with an explanation/comments

   #include <stdio.h>
    #define TEST(v,x) (countBits(v) == x) ? puts("Passed") : 
    puts("Failed")




    //Function prototype


     //unsigned char countBits(const unsigned char u);




   


    //This function passes different values to the function countBits, and 
    checks the returned value is correct


    // int main(int argc, const char * argv[]) {
     puts("Begin tests");
     TEST(0, 0);             //Minimum edge case
   
     TEST(1u, 1);            //smallest for 1 result
     TEST(1u<<1, 1);
     TEST(1u<<7, 1);         //largest for 1 result
   
     TEST(0x03, 2);          //Smallest for 2 result
     TEST(0xC0, 2);          //Largest for 2 result
   
     TEST(0xFF, 8);          //Maximum edge case
   
     return 0;
      }


    //FUNCTION UNDER TEST


    // Function countBits
    //
    // Return value: returns the number of '1's in the binary 
    representation of u
    //
    // Examples.
    // If u = 12, this is represented as binary 00001100
    // There are two '1's in this number, so the function will return 2
    //
    // If u = 13, this is represented as binary 00001101
    // There are three '1's in this number, so the function will return 3
    //
    unsigned char countBits(const unsigned char u)
    {
     unsigned char numberOfBits = 0;
     //  BEGIN  CODE HERE 




      
  
     return numberOfBits;
      }

Also, could someone show me a simple example code to demonstrate the 'switch-case' and 'if-else if else' and statements with comments/ explanation?












And this code-

 unsigned short x1;


    /*
     * The code below is supposed to request the user to input 
    a numeric value
     * If the value is not between 20 and 50, it should ask 
    again
     * If 20 <= x <= 50, then the code should proceed.
     *
     * where are the bugs?
     * only use while loop
     */
    


    do {
        puts("Enter a whole number x, such that 20 <= x <= 
    50");
        scanf("%hu", x1);
    } while ( (x1>=20) && (x1 <50) );

[GReaper]

You haven't done anything though. The code you posted and the questions you ask seem like homework, try to solve them instead of asking for freebies.

[HappyC4mper]

i've only had 2 days crash course of c so far and these are just practice questions. I just want someone to explain how I could do it. Since I'll be using what i've learnt from these practice questions to program a robot next week :/

[Salem]

Well do you know what << does?
What about other bitwise operators like & | !

What you need is a loop which rotates a 1-bit through every position so you can test your value.

Your over ambitious times are another issue...