Loops and Decision Control Statements in C++
1. Loops
Loops are used to execute a block of code repeatedly until a condition is met.
1.1. for Loop
The for loop is used when the number of iterations is known beforehand.
for (int i = 0; i < 5; i++) {
cout << "Iteration: " << i << endl;
}Explanation:
- Initialization:
int i = 0 - Condition:
i < 5 - Update:
i++(increment after each iteration)
1.2. while Loop
The while loop repeats a block of code while the condition is true.
int i = 0;
while (i < 5) {
cout << "Iteration: " << i << endl;
i++;
}1.3. do-while Loop
The do-while loop guarantees at least one execution of the code block before checking the condition.
int i = 0;
do {
cout << "Iteration: " << i << endl;
i++;
} while (i < 5);2. Decision Control Statements
Decision control statements allow conditional execution of code.
2.1. if Statement
The if statement executes a block of code only if the condition is true.
int x = 10;
if (x > 5) {
cout << "x is greater than 5";
}2.2. if-else Statement
The if-else statement executes one block of code if the condition is true, and another block if it’s false.
int x = 3;
if (x > 5) {
cout << "x is greater than 5";
} else {
cout << "x is less than or equal to 5";
}2.3. switch Statement
The switch statement evaluates an expression and executes the matching case.
int day = 2;
switch (day) {
case 1: cout << "Monday"; break;
case 2: cout << "Tuesday"; break;
default: cout << "Invalid day";
}2.4. Conditional Operator (?:)
A shorthand for the if-else statement.
int x = 5;
int y = (x > 3) ? 10 : 0;Explanation: If x is greater than 3, y is assigned 10, otherwise 0.
3. Other Control Statements
3.1. break
break is used to exit a loop or switch statement.
for (int i = 0; i < 10; i++) {
if (i == 5) break;
cout << i << endl;
}3.2. continue
continue skips the current iteration and moves to the next iteration of the loop.
for (int i = 0; i < 10; i++) {
if (i == 5) continue;
cout << i << endl;
}3.3. goto
goto transfers control to a labeled statement, but it is generally discouraged due to making code harder to understand.
int x = 0;
label:
cout << "This is a goto example." << endl;
x++;
if (x < 5) goto label;Structures and Functions in C++
1. Structures
Structures in C++ are used to group different data types into a single unit.
struct Person {
string name;
int age;
};Example:
Person p1;
p1.name = "John";
p1.age = 25;1.1. Accessing Structure Members
Structure members can be accessed using the dot . operator.
cout << p1.name << endl;
cout << p1.age << endl;1.2. Structure Within a Structure
You can nest one structure inside another.
struct Address {
string city;
int zipCode;
};
struct Person {
string name;
Address addr;
};1.3. Enumerated Data Type
Enums are user-defined data types that consist of named integer constants.
enum Weekday { Monday, Tuesday, Wednesday };
Weekday today = Monday;2. Functions
Functions allow code to be reused and organized.
2.1. Simple Functions
A function is defined using the syntax:
int add(int a, int b) {
return a + b;
}Call the function using:
int result = add(3, 4);
cout << result;2.2. Passing Arguments to Functions
Arguments can be passed by value, meaning a copy is made.
void increment(int a) {
a++;
}2.3. Returning Values from Functions
Functions can return values to the calling code.
int square(int x) {
return x * x;
}2.4. Reference Arguments
Arguments can also be passed by reference using the & symbol. This allows the function to modify the actual variable.
void increment(int &a) {
a++;
}2.5. Overloaded Functions
Multiple functions with the same name can exist as long as they have different parameters.
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}3. Storage Classes
Storage classes define the lifetime and visibility of a variable.
- auto: Default storage class for local variables.
- static: Variable retains its value between function calls.
- extern: Variable defined outside of the current scope.
- register: Stores the variable in a CPU register for faster access.
Example:
void counter() {
static int count = 0;
count++;
cout << count;
}4. Scope Resolution Operator (::)
The :: operator is used to define a function outside of its class or access a global variable that is overshadowed by a local one.
class MyClass {
public:
void print();
};
void MyClass::print() {
cout << "Hello, World!";
}