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A-3 Loops
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  1 int main()                               |main ()
  2 {                                        |{
  3     int sum = 0;                         |  int j;
  4     int i, j;                            |  int i;
  5                                          |  int sum;
  6                                          |  int D.1718;
  7                                          |
  8     while(sum < 100) {                   |<bb 2>:
  9         sum = sum * 2;                   |  sum = 0;
 10     }                                    |  goto <bb 4>;
 11                                          |
 12                                          |<bb 3>:
 13                                          |  sum = sum * 2;
 14                                          |
 15                                          |<bb 4>:
 16                                          |  if (sum <= 99)
 17                                          |    goto <bb 3>;
 18                                          |  else
 19                                          |    goto <bb 5>;
 20                                          |
 21     for(i=0; i<25; i++) {                |<bb 5>:
 22         for(j=0; j<50; j++) {            |  i = 0;
 23             sum = sum + i*j;             |  goto <bb 10>;
 24         }                                |
 25     }                                    |<bb 6>:
 26 }                                        |  j = 0;
 27                                          |  goto <bb 8>;
 28                                          |
 29                                          |<bb 7>:
 30                                          |  D.1718 = i * j;
 31                                          |  sum = D.1718 + sum;
 32                                          |  j = j + 1;
 33                                          |
 34                                          |<bb 8>:
 35                                          |  if (j <= 49)
 36                                          |    goto <bb 7>;
 37                                          |  else
 38                                          |    goto <bb 9>;
 39                                          |
 40                                          |<bb 9>:
 41                                          |  i = i + 1;
 42                                          |
 43                                          |<bb 10>:                                    
 44                                          |  if (i <= 24)                              
 45                                          |    goto <bb 6>;                            
 46                                          |  else                                      
 47                                          |    goto <bb 11>;                           
 48                                          |                                            
 49                                          |<bb 11>:                                    
 50                                          |  return;                                   
 51                                          |                                            
 52                                          |}                 
 
 
 
Solutions
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        1   Basic blocks 2,  3 and 4 correspond to the  while-loop. A while loop
            is  nothing but  a  set  of basic  blocks  with conditional  control
            transfer, the only  notable difference being a jump to  a block that
            has been previously executed (i.e. a backward branch).

        2   A  for-loop  is  nothing  but  a  while-loop  with  the  initializer
            separated out  into an  initial basic  block, the  body of  the loop
            subsequently, the  increment part at the  end of the loop  body, and
            the conditional jump back to the start of the loop.