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Lab 1 Solutions
6.096 Staff
1 “Hello, World” (10 points)
1.1 Hello World I (1 point)
1 # include < iostream > 2 3 using namespace std ; 4 5 int main () 6 { 7 const char * str = " Hello , World! " ; 8 cout << str << " \ n " ; 9 return 0; 10 }
1.2 Hello World II (9 points)
1. for loop: (3 points)
1 # include < iostream > 2 3 using namespace std ; 4 5 int main () 6 { 7 int N ; 8 cin >> N ; 9 for (; N - - > 0;) 10 { 11 cout << " Hello , World !\ n " ; 12 } 13 return 0; 14 }
2. while loop: (3 points)
1 # include < iostream > 2 3 using namespace std ; 4 5 int main () 6 { 7 int N ; 8 cin >> N ; 9 while (N - - > 0) 10 { 11 cout << " Hello , World !\ n " 12 } 13 return 0; 14 }
3. do...while loop: (3 points)
include < iostream >
using namespace std ;
int main () { int N ; cin >> N ; do { cout << " Hello , World !\ n " ; } while ( - - N > 0) ; return 0; }
29 maxVal = a ; 30 } 31 } 32 33 cout << " Mean : " << ( double ) acc / N << " \ n " ; 34 cout << " Max : " << maxVal << " \ n " ; 35 cout << " Min : " << minVal << " \ n " ; 36 cout << " Range : " << ( maxVal - minVal ) << " \ n " ; 37 38 return 0; 39 }
2.3 Prime Numbers (10 points)
1 # include < iostream > 2 3 using namespace std ; 4 5 int main () 6 { 7 int N ; 8 cin >> N ; 9 for ( int i = 2; N > 0; ++ i ) 10 { 11 bool isPrime = true ; 12 for ( int j = 2; j < i ; ++ j ) 13 { 14 if ( i % j == 0) 15 { 16 isPrime = false ; 17 break ; 18 } 19 } 20 if ( isPrime ) 21 { 22 --N ; 23 cout << i << " \ n " ; 24 } 25 } 26 return 0; 27 }
2.4 Multiples of numbers (10 points)
2.4.1 Ternary operator (3 points)
1 # include < iostream > 2 3 using namespace std ; 4 5 int main () 6 { 7 while (1) 8 { 9 int N ; 10 cin >> N ; 11 cout << (( N % 5 == 0 && N >= 0)? N /5 : -1) << " \ n " ; 12 } 13 return 0; 14 }
2.4.2 continue (3 points)
1 # include < iostream > 2 3 using namespace std ; 4 5 int main () 6 { 7 while (1) 8 { 9 int N ; 10 cin >> N ; 11 if ( N % 5 > 0) 12 { 13 cout << " -1\ n " ; 14 continue ; 15 } 16 cout << N /5 << " \ n " ; 17 } 18 return 0; 19 }
2.4.3 break (3 points)
3 Factorials Gone Wrong (40 points)
3.1 Writing the factorial program (5 points)
3.2 Breaking the program (5 points)
If − 1 is entered, the program will output 1, which is incorrect because the factorial function
(or Gamma function) is not defined for negative numbers.
3.3 Breaking the program II (5 points)
The number at which the program fails depends on the system architecture; 64-bit systems
often fail at 17. We accepted any answer around that value.
3.4 Rewriting Factorial (10 points)
1 # include < iostream > 2 3 using namespace std ; 4 5 long long accumulator = 1; 6 7 int main () 8 { 9 int number ; 10 cout << " Enter a number : " ; 11 cin >> number ; 12 if ( number < 0) 13 { 14 cout << " No negative numbers allowed !\ n " ; 15 return 1; 16 } 17 if ( number > 20) 18 { 19 cout << " Program will not produce correct result !\ n " ; 20 } 21 for (; number > 0; accumulator *= number - -) ; 22 cout << " The factorial of " << number << " is " << accumulator << " .\ n " ; 23 return 0; 24 }
3.5 Rewriting Factorial II (10 points)
include < iostream >
using namespace std ;
int main () { int number ; cout << " Enter a number : " ; cin >> number ; switch ( number ) { case 0: case 1: cout << " 1\ n " ; break ; case 2: cout << " 2\ n " ; break ; case 3: cout << " 6\ n " ; break ; case 4: cout << " 24\ n " ; break ; case 5: cout << " 120\ n " ; break ; case 6: cout << " 720\ n " ; break ; case 7: cout << " 5040\ n "; break ; case 8: cout << " 40320\ n " ; break ; case 9: cout << " 362880\ n " ; break ; case 10: cout << " 3628800\ n " ; break ; default :
