> For the complete documentation index, see [llms.txt](https://learncpp.benntan.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://learncpp.benntan.com/cpp-fundamentals/control-flow.md).
# 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 %}
---
# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.
## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.
Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:
```
GET https://learncpp.benntan.com/cpp-fundamentals/control-flow.md?ask=&goal=
```
`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.
Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.