C H.W

typedef struct { int sid; int tel; } STUDENTX; STUDENTX sx[5]; // This looks like below

sx[0] sx[1] sx[2] sx[3] sx[4]

sid sid sid sid sid

tel tel tel tel tel

sx[0].sid = 44; sx[0].sid = 12;

sx[1].sid = 14; sx[1].sid = 32;

sx[2].sid = 24; sx[2].sid = 11;

sx[3].sid = 54; sx[3].sid = 14; // after these assignments, sx[] looks like below

sx[0] sx[1] sx[2] sx[3] sx[4]

44 14 24 54 sid

12 32 11 14 tel

STUDENTX *ptr[5];

ptr[0] = &sx[0];

ptr[1] = &sx[1];

ptr[2] = &sx[2];

ptr[3] = &sx[3];

ptr[4] = &sx[4]; //after these pointer assignments, ptr[] looks like below

ptr[0] ptr[1] ptr[2] ptr[3] ptr[4]

&sx[0] &sx[1] &sx[2] &sx[3] &sx[4]

sx[0] sx[1] sx[2] sx[3] sx[4]

44 14 24 54 sid

12 32 11 14 tel

STUDENTX *t;

t = ptr[1]; // t = &sx[1]

ptr[1] = ptr[2]; // ptr[1] = &sx[2]

ptr[2] = t; // ptr[2] = &sx[1]

ptr[0] ptr[1] ptr[2] ptr[3] ptr[4]

&sx[0] &sx[2] &sx[1] &sx[3] &sx[4]

sx[0] sx[1] sx[2] sx[3] sx[4]

44 14 24 54 sid

12 32 11 14 tel

Bubble sort using the pointers.

sorted = 0; // this is to go into the while loop.

while( sorted == 0) // while not sorted, we do below

{

sorted = 1; // let's assume it is sorted

for(i=0; i<NUM-1; i++) // i gose 0 to NUM-2, and (i+1) goes 1 to NUM-1

{ STUDENTX *t; // t will contain address of data of STUDENT type

if( ptr[i]->sid > ptr[i+1]->sid ) // compare sid,

{ t = ptr[i];

ptr[i] = ptr[i+1];

ptr[i+1] = t;

sorted = 0; // ahhhh, not sorted yet

}

}

// at this point, if sorted is still 1, every pair was in order, thus sorted.

}