Control Structures 
           Sequence 
           Statements execute in sequence, one after the other, such as the following solution for a 
           quadratic equation: 
            
             double desc, x1, x2; 
             desc = b * b – 4 * a * c; 
             desc = sqrt(desc); 
             x1 = (-b - desc) / 2 * a; 
             x2 = (-b + desc) / 2 * a; 
            
           Statements may appear in a block or compound statement: 
            
             { 
               double desc, x1, x2; 
               desc = b * b – 4 * a * c; 
               desc = sqrt(desc); 
               x1 = (-b - desc) / 2 * a; 
               x2 = (-b + desc) / 2 * a; 
             } 
              
           In C all definitions must be at the beginning of a block. In C++ you may define variables at any 
           point in the code: 
            
             { 
               double desc = b * b – 4 * a * c; 
               desc = sqrt(desc); 
               double x1 = (-b - desc) / 2 * a; 
               double x2 = (-b + desc) / 2 * a; 
             } 
            
           Variables defined in a block are local to that block and override global variables and variables in 
           outer blocks with the same name. 
            
             { 
               int a = 1, b = 2; 
               cout << a << b << endl; 
              { 
                 int a = 3; 
                 cout << a << b << endl; 
              } 
               cout << a << b << endl; 
             } 
            
           The above code outputs the following: 
            
             12 
             32 
             12 
               
            Selection 
            If Statement 
            The general form of the if and if-else statements follow: 
             
               if (condition) 
                statement 
                
               if (condition) 
                statement 
               else 
                statement 
                
            A statement may be a single statement terminated by a semicolon, or a compound statement. For 
            example: 
             
               int g;       // grade, 0..100 
                
               if (g > 50) 
                 cout << "passed" << endl; 
                
               if (g > 50) 
                 cout << "passed" << endl; 
               else 
                 cout << "failed" << endl; 
                
               if (g > 50) { 
                 cout << "passed" << endl; 
                 cout << "good job" << endl; 
               } else { 
                 cout << "failed" << endl; 
                 cout << "bad job" << endl; 
               } 
             
            What does the following code output if the grade is 10? 
             
               if (g > 50) 
                 cout << "passed" << endl; 
                 cout << "good job" << endl; 
                
            What does the following code output if grade is zero? 
             
               if (grade = 0) 
                 cout << "failed" << endl; 
                Nested If 
                Recall that control structures may be nested. Lets nest an If  statement within another If 
                statement: 
                 
                   if (g > 50) 
                   if (g > 90) 
                   cout << "super" << endl; 
                   else 
                   cout << "good" << endl; 
                   else 
                   if (g > 25) 
                   cout << "fair" << endl; 
                   else 
                   cout << "poor" << endl; 
                    
                Well, that's a bit hard to read. Let's rewrite it with proper indenting: 
                 
                   if (g > 50) 
                      if (g > 90) 
                         cout << "super" << endl;    // g = 91..100 
                    else 
                         cout << "good" << endl;     // g = 51..90 
                   else 
                      if (g > 25) 
                         cout << "fair" << endl;     // g = 26..50 
                    else 
                         cout << "poor" << endl;     // g = 0..25 
                 
                What is the output for the following code if the grade is 20? 
                 
                   if (g > 50) 
                   if (g > 90) 
                   cout << "pt1"; 
                   else 
                   cout << "pt2"; 
                Ternary Conditional Operator 
                The following code evaluates i and j, placing the smallest number in min: 
                 
                   if (i < j) 
                      min = i; 
                   else 
                      min = j; 
                 
                Let's use the ternary operator to accomplish the same logic: 
                 
                   min = i < j ? i : j; 
                 
                The general form is as follows: 
                 
                   condition ? trueExpression : falseExpression 
                 
                If the condition evaluates to true (non-zero) then trueExpression is returned. Otherwise, 
                falseExpression is returned. Not meant as a substitute for If-Else, ternary operators sometimes 
                simplify logic. This is illustrated below, in a min function: 
                    
                   int min(int x, int y) {             int min(int x, int y) { 
                    int t;          return (x < y) ? x : y; 
                    if (x < y)        } 
                     t = x; 
                    else 
                     t = y; 
                    return t; 
                   } 
                Switch Statement 
                If you are repeatedly testing a variable for constant values, consider using the switch statement 
                instead of an if-else statement: 
                 
                   if (a == 1)        switch(a) { 
                    x = 5;        case 1: 
                   else if (a == 3)       x = 5; 
                    x = 10;         break; 
                   else if (a == 5)      case 3: 
                    x = 15;         x = 10; 
                   else if (a == 6)       break; 
                    x = 15;        case 5: 
                   else          case 6: 
                    x = 100;         x = 15; 
                               break; 
                              default: 
                               x = 100; 
                              } 
                 
                Control transfers directly to the appropriate case, then falls through until there is a break 
                statement. On a break, control transfers to the next sequential statement after the switch 
                statement.