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Control Flow in C++

Switch Statements

A switch statement provides a means of checking an expression against various cases. If there is a match, the code within starts to execute.

The break keyword can be used to terminate a case. If the break keyword is missing from a case, it will cause code execution to overflow to subsequent cases.

The code within the default block is executed when no other case matches.

switch (grade) {
  case 9:
    std::cout << "Freshman\n";
    break;
  case 10:
    std::cout << "Sophomore\n";
    break;
  case 11:
    std::cout << "Junior\n";
    break;
  case 12:
    std::cout << "Senior\n";
    break;
  default:
    std::cout << "Invalid\n";
    break;
}

Loops

In C++, loops repeatedly execute code as long as the provided condition is true.

There are four main types of loops in C++:

  1. while loops: repeats a block of code as long as the given boolean condition is true.
  2. do-while loops: similar to while loops, but run at least once.
  3. for loops: repeats a block of code a specific number of times.
  4. for-each loops: used to iterate through every item in an array or list-like structure.
// while loop
int count = 0;
while (count <= 10) {
  std::cout << count;
  count++;
}


// do-while loop
int price = 300;
do {
  std::cout << "Too expensive!";
} while (price > 500);


// for loop
for (int i = 0; i <= 10; i++) {
  std::cout << i;
}


// for-each loop
int fibonacci[5] = { 0, 1, 1, 2, 3 };
for (auto number:fibonacci){
  std::cout << number;
}

if Statement

An if statement is used to test an expression for truth.

  • If the condition evaluates to true, then the code within the block is executed; otherwise, it will be skipped.
if (a == 10) {
  // Code goes here
}

else Clause

An else clause can be added to an if statement.

  • If the condition evaluates to true, code in the if part is executed.
  • If the condition evaluates to false, code in the else part is executed.
if (year == 1991) {
  // This runs if it is true
}
else {
  // This runs if it is false
}

Relational Operators

Relational operators are used to compare two values and return true or false depending on the comparison:

  • == equal to

  • != not equal to

  • > greater than

  • < less than

  • >= greater than or equal to

  • <= less than or equal to

if (a > 10) {
   // ☝️ means greater than
}

else if Statement

One or more else if statements can be added in between the if and else to provide additional condition(s) to check.

if (apple > 8) {
  // Some code here
}
else if (apple > 6) {
  // Some code here
}
else {
  // Some code here
}

Conditional Statements

Conditional statements are used to control the flow of code execution by testing for a condition for truth.

  • if statements execute code only if the provided condition is true.
  • else statements execute code only if the provided condition in the if statement is false.
  • one or more else if statements can be added in between the if and else to provide additional condition(s) to check.

Some useful tricks with conditional statements:

  • It is possible to condense an if-else expression into a single statement using the following syntax:
variable = (condition) ? condition_is_true : condition_is_false;
  • Curly brackets { } may be omitted if there is only a single statement inside a conditional statement.
int temperature = 60;


if (temperature < 65) {
  std::cout << "Too cold!";
}
else if (temperature > 75) {
  std::cout << "Too hot!";
}
else	// brackets may be omitted here
  std::cout << "Just right...";

Break and Continue

In C++, the break keyword is used to exit a switch or loop.

The continue keyword is used to skip an iteration of a loop.

// Prints: 0123
for (int i = 0; i < 10; i++) {
  if (i == 4) {
    break;
  }
  std::cout << i;
}


// Prints: 012356789
for (int i = 0; i < 10; i++) {
  if (i == 4) {
    continue;
  }
  std::cout << i;
}
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