Example 8: Even/Odd Loop
Modulo operator and conditional processing in loops
Download file bucle🎯 Live Demo
Number Analysis (0-50)
📋 Latest Evens:
📋 Latest Odds:
Change the analysis limit!
Quick limits:
🔢 Real-Time Calculation:
📖 Code Explanation
Complete PHP Code
<?php
$numero = 50;
$suma = 0;
for ($i = 0; $i <= $numero; $i++) {
if ($i % 2 == 0) {
print($i);
} else {
$suma += $i;
}
}
print("La suma total de impares es: \$suma");
?>📝 Lines 1-2: Initial variables
$numero = 50;$suma = 0;
What does it do? Defines the analysis limit and initializes the accumulator variable.
Why is it done this way? $suma must start at 0 in order to accumulate values correctly.
💡 Concept: Accumulator variables
Variables like $suma are used to accumulate values during a loop. They must be initialized before the loop.
📝 Line 4: Loop for
for ($i = 0; $i <= $numero; $i++) {
What does it do? Creates a loop that goes through all numbers from 0 up to the limit.
Why is it done this way? for loop is perfect for traversing known numeric ranges.
💡 Concept: Inclusive range
We use <= instead of < to include the limit number in the analysis.
📝 Lines 5-9: Condition with modulo operator
if ($i % 2 == 0) { print($i);} else { $suma += $i;}
What does it do? Uses the modulo operator to determine whether a number is even or odd.
Why is it done this way? The % operator returns the remainder of a division, perfect for checking parity.
💡 Concept: Modulo operator (%)
$i % 2 returns 0 if $i is even, 1 if it's odd. It's the most efficient way to check parity.
📝 Compound assignment operator
$suma += $i;
What does it do? Equivalent to $suma = $suma + $i. Accumulates the current value into the total sum.
Why is it done this way? More compact and readable than the expanded form.
💡 Concept: Compound operators
+= adds and assigns
-= subtracts and assigns
*= multiplies and assigns
/= divides and assigns
➗ Modulo Operator in Depth
What is the modulo operator?
The % operator returns the remainder of a division between two numbers.
10 % 3
= 1
(10 ÷ 3 = 3 with remainder 1)
15 % 5
= 0
(15 ÷ 5 = 3 exact)
7 % 2
= 1
(7 ÷ 2 = 3 with remainder 1 → odd)
8 % 2
= 0
(8 ÷ 2 = 4 exact → even)
Common uses of modulo
🔍 Check parity
if ($numero % 2 == 0)
Determines whether a number is even or odd
🔄 Alternate elements
if ($i % 3 == 0)
Apply style every 3 elements
⏰ Time conversion
$minutos = $segundos % 60
Extract minutes from total seconds
🎯 Cyclic groups
$grupo = $numero % 5
Assign to groups of 5 elements
🎯 Loop Processing Patterns
Filtering and Classification
$pares = [];
$impares = [];
foreach ($numeros as $num) {
if ($num % 2 == 0) {
$pares[] = $num;
} else {
$impares[] = $num;
}
}Separate elements into different categories based on conditions.
Accumulation Conditional
$suma_condicional = 0;
for ($i = 0; $i <= 100; $i++) {
if ($i % 3 == 0) {
$suma_condicional += $i;
}
}Add up only the elements that meet a certain condition.
Counting and Statistics
$contador = 0;
foreach ($datos as $dato) {
if ($dato > $umbral) {
$contador++;
}
}Count elements that meet specific criteria.
⚡ Optimization and Best Practices
✅ Initialize variables
Always initialize accumulator variables before the loop.
✅ Correct
$suma = 0;
for(...) { $suma += ... }
❌ Incorrect
for(...) { $suma += ... }
✅ Use compound operators
Operators like += are more efficient and readable.
✅ Better
$suma += $valor;
❌ Worse
$suma = $suma + $valor;
✅ Choose the right loop
Use for for ranges, foreach for arrays.
✅ Appropriate
for ($i=0; $i<10; $i++)
❌ Inappropriate
foreach (range(0,9) as $i)
🎯 Key Concepts Learned
Modulo Operator
- Returns the remainder of a division
- Perfect for checking divisibility
- Used for parity, grouping, cycles
$a % $b= remainder of a ÷ b
Conditional Processing
- Run different actions based on conditions
- Combine loops with if-else
- Classify and filter data
- Selectively accumulate values
Accumulator Variables
- Store cumulative results
- Must be initialized before the loop
- Can be sums, counters, etc.
- Use compound operators
💪 Practical Exercise
Extend the analysis system
Practice these changes to improve your skills:
- Modify the code to also calculate the sum of even numbers
- Implement a counter for numbers divisible by 3 and 5 at the same time
- Create a system that finds prime numbers in the range
- Add separate average calculations for even and odd numbers
- Implement a function that receives the limit and returns complete statistics
Solution 1: Sum of evens
<?php
$suma_pares = 0;
$suma_impares = 0;
for ($i = 0; $i <= $limite; $i++) {
if ($i % 2 == 0) {
$suma_pares += $i;
} else {
$suma_impares += $i;
}
}
echo "Suma pares: $suma_pares, Suma impares: $suma_impares";
?>Solution 2: Divisible by 3 and 5
<?php
$divisibles = 0;
for ($i = 0; $i <= $limite; $i++) {
if ($i % 3 == 0 && $i % 5 == 0) {
$divisibles++;
}
}
echo "Números divisibles por 3 y 5: $divisibles";
?>Solution 3: Prime numbers
<?php
$primos = [];
for ($i = 2; $i <= $limite; $i++) {
$esPrimo = true;
for ($j = 2; $j < $i; $j++) {
if ($i % $j == 0) {
$esPrimo = false;
break;
}
}
if ($esPrimo) {
$primos[] = $i;
}
}
echo "Números primos: " . implode(', ', $primos);
?>Solution 4: Averages
<?php
$pares = [];
$impares = [];
for ($i = 0; $i <= $limite; $i++) {
if ($i % 2 == 0) {
$pares[] = $i;
} else {
$impares[] = $i;
}
}
$promedio_pares = count($pares) > 0 ? array_sum($pares) / count($pares) : 0;
$promedio_impares = count($impares) > 0 ? array_sum($impares) / count($impares) : 0;
echo "Promedio pares: $promedio_pares, Promedio impares: $promedio_impares";
?>Solution 5: Function for statistics
<?php
function analizarNumeros($limite) {
$estadisticas = [
'pares' => [],
'impares' => [],
'suma_pares' => 0,
'suma_impares' => 0
];
for ($i = 0; $i <= $limite; $i++) {
if ($i % 2 == 0) {
$estadisticas['pares'][] = $i;
$estadisticas['suma_pares'] += $i;
} else {
$estadisticas['impares'][] = $i;
$estadisticas['suma_impares'] += $i;
}
}
return $estadisticas;
}
$resultados = analizarNumeros(50);
print_r($resultados);
?>