Decision and Repetition Loops: The Essential Guide for Beginners

Programming is, essentially, teaching the computer to make decisions and repeat actions. This is done through control structures, which are fundamental in any programming language. In this article, we will explore the main concepts of decision loops and repetition loops, with practical examples.

Decision Loops

Decision loops, also known as conditional structures, allow the program to choose different paths based on certain conditions. The main concept here is to check whether a condition is true or false.

if, else if, else

The most common conditional structure is if. It checks a condition; if true, executes a block of code. Otherwise, you can follow with else if or else to test other conditions or provide an alternative.

Example in Python:

idade = 18

if idade >= 18:
    print("Você é maior de idade.")
elif idade > 12:
    print("Você é adolescente.")
else:
    print("Você é criança.")

switch/case (or match)

In some languages, such as JavaScript or C, the switch/case allows checking multiple conditions more efficiently than multiple if/else.

Example in JavaScript:

let cor = "verde";

switch (cor) {
    case "vermelho":
        console.log("Pare!");
        break;
    case "amarelo":
        console.log("Atenção!");
        break;
    case "verde":
        console.log("Siga em frente!");
        break;
    default:
        console.log("Cor desconhecida.");
}

Ternary

In languages ​​like Python, JavaScript and Java, we can use ternary operators to make simple decisions in a single line.

Example in Python:

idade = 18
print("Maior de idade" if idade >= 18 else "Menor de idade")

Repeating Loops

Repeat loops are used to execute a block of code multiple times. The most common structures are for, while and do-while.

for

For is used when we know in advance the number of times a block of code must be repeated. It is very useful for iterating over lists, arrays and sequences.

Example in Python:

for i in range(5):
    print(f"Este é o loop número {i + 1}")

Example in JavaScript:

const frutas = ["Maçã", "Banana", "Laranja"];
for (let i = 0; i < frutas.length; i++) {
    console.log(frutas[i]);
}

while

While repeats a block of code as long as a condition is true. This type of loop is used when we don't know the exact number of repetitions in advance.

Example in Python:

contador = 0
while contador < 5:
    print(f"Contagem: {contador}")
    contador += 1

do-while

Do-while is similar to while, but it guarantees that the code within the block is executed at least once, even if the condition is false from the beginning.

Example in JavaScript:

let contador = 0;
do {
    console.log(`Contagem: ${contador}`);
    contador++;
} while (contador < 5);

Flow Control in Loops

In addition to making decisions and repeating actions, it is often necessary to control the flow within loops, for example, interrupting or skipping iterations.

break

The break keyword breaks the loop immediately, skipping any future iterations.

Example in Python:

for i in range(10):
    if i == 5:
        break
    print(i)

Output:

0
1
2
3
4

continue

The continue keyword skips to the next iteration of the loop, ignoring the rest of the code within the current iteration.

Example in Python:

for i in range(5):
    if i == 2:
        continue
    print(i)

Output:

0
1
3
4

Conclusion

Decision and repetition loops are the backbone of any program. They allow us to create dynamic flows, where behavior changes based on inputs and conditions encountered. Mastering these concepts is crucial to becoming an efficient programmer, as they appear in virtually every code you will write.

Remember to choose the appropriate structure for each situation and, with practice, you will soon be able to write clean and efficient code using these loops.

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