# Control Flow
So far, our programs have executed line-by-line, step-by-step from top to bottom. In the real world however, we might want to
* make decisons based on a condition
* repeat certain actions
* organise logic into reusable pieces
This is where **control flow** comes in
### Conditionals
Conditionals let our program make decisions.
{% code title="main.cpp" %}
```cpp
int score = 85;
if (score == 100) {
std::cout << "Perfect" << std::endl;
} else if (score >= 90) {
std::cout << "Grade A" << std::endl;
} else if (score >= 80) {
std::cout << "Grade B" << std::endl;
} else if (score >= 70) {
std::cout << "Grade C" << std::endl;
} else {
std::cout << "Needs improvement" << std::endl;
}
```
{% endcode %}
{% hint style="info" %}
⚠️ Common Pitfall
`=` means assignment while `==` checks for equality
{% code title="" %}
```cpp
int x = 5; // assignment
x == 5; // comparison
```
{% endcode %}
{% endhint %}
### Loops
Loops lets us repeat certain blocks of code
#### while loop
A `while` loop keeps running as long as the condition is fufilled.
Code
Output
int x = 1;
while (x <= 5) {
std::cout << x << std::endl;
x++;
}
#### for loop
A `for` loop is useful when we know how many times we want to repeat something.
for (int i = 1; i <= 5; i++) {
std::cout << i << std::endl;
}
#### break / continue
`break` forces the loop to terminate prematurely.
`continue` skips the rest of the current iteration.
for (int i = 1; i <= 5; i++) {
if (i == 3) {
break;
}
std::cout << i << std::endl;
}
for (int i = 1; i <= 5; i++) {
if (i == 3) {
continue;
}
std::cout << i << std::endl;
}
### Functions
Functions let us group code into reusable blocks.
#### Basic Usage
{% code title="main.cpp" %}
```cpp
#include
void greet() {
std::cout << "Hello!" << std::endl;
}
int main() {
greet();
}
```
{% endcode %}
Here:
* `void` means the function does not return anything
* `greet` is the function name
* `greet()` *calls* the function, causing **Hello!** to be printed.
#### Function Parameters
Our current `greet` function always print the same message (which isn't very flexible). Let's augment it by adding a parameter so that our greeting message can change depending on the person.
{% code title="main.cpp" %}
```cpp
#include
void greet(std::string name) {
std::cout << "Hello, " << name << "!" << std::endl;
}
int main() {
greet("Benn");
greet("Bryan");
greet("Anton Tim");
}
```
{% endcode %}
#### Functions Return Value
A return value is the value the function sends back to the caller after it's done executing. At the call site, you can use the result however you wish.
{% code title="main.cpp" %}
```cpp
#include
int add(int x, int y) {
return x + y;
}
int main() {
int result = add(3, 4);
std::cout << result << std::endl;
}
```
{% endcode %}
### Exercise(s)
⭐ Write a function `countdown(int n)` that takes in a number `n` and prints from `n` down to 1.
{% code title="" %}
```shellscript
countdown(5)
5
4
3
2
1
```
{% endcode %}
⭐⭐ Write a program that hardcodes a secret number. It will repeatedly ask the user to guess. Depending on the user's guess, the program will feedback **Too low, Too high** or **Correct.**
{% code title="" %}
```
Guess the number: 50
Too high
Guess the number: 25
Too low
Guess the number: 30
Too low
Guess the number: 42
Correct!
```
{% endcode %}
.png?alt=media&token=b53fa0d5-34ff-4e82-94eb-825cdf918c80)
