JavaScriptにおけるループ

What is Looping? And why do we use it? Loops are used to execute a block of code repeatedly without writing the same code multiple times. They help reduce code repetition and make programs more efficient. example: without looping: console . log ( 1 ); console . log ( 2 ); console . log ( 3 ); console . log ( 4 ); console . log ( 5 ); with looping: for loop Syntax for ( initialization ; condition ; increment ){ // code } for ( let i = 1 ; i <= 5 ; i ++ ){ console . log ( i ); } This also gives me the same output, but the code is reduced to be smart. output is: 1 2 3 4 5 Print Numbers from 5 to 1 for ( let i = 5 ; i >= 1 ; i -- ){ console . log ( i ); } Explanation i is initialized with 5. The loop runs while i >= 1. console.log(i) prints the current value of i. i-- decreases the value by 1 after each iteration. When i becomes 0, the condition 0 >= 1 is false, so the loop stops. Output 5 4 3 2 1 Expected Output 1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz program for ( let a = 1 ; a <= 10 ; a ++ ) { if ( a % 3 == 0 ) { console . log ( " Fizz " ); } else if ( a % 5 == 0 ) { console . log ( " Buzz " ); } else { console . log ( a ); } } Explanation a is initialized with 1. The loop runs while a <= 10. If a is divisible by 3, it prints "Fizz". Else if a is divisible by 5, it prints "Buzz". Otherwise, it prints the number. After each iteration, a++ increases the value by 1. The loop stops when a becomes 11 because the condition 11 <= 10 is false. output 1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz Print Odd Numbers Using continue Expected Output 1 3 5 7 9 Program for ( let i = 1 ; i <= 10 ; i ++ ) { if ( i % 2 == 0 ) { continue ; } console . log ( i ); } Explanation i is initialized with 1. The loop runs while i <= 10. If i is an even number, continue skips the current iteration. Only odd numbers reach console.log(i). After each iteration, i++ increases the value by 1. The loop stops when i becomes 11 because the condition 11 <= 10 is false. Output 1 3 5 7 9 Expected Output 1 2 3 4 5 program for ( let i = 1 ; i <= 10 ; i ++ ) { if ( i == 6 ) { break ; } console . log ( i ); } Explanation i is initialized with 1. The loop runs while i <= 10. When i becomes 6, the break statement stops the loop immediately. Since the loop stops before console.log(i), 6 is not printed. The loop ends without checking the remaining values. Output 1 2 3 4 5 Expected Output 1 3 program for ( let i = 1 ; i <= 5 ; i ++ ) { if ( i === 2 ) { continue ; } if ( i === 4 ) { break ; } console . log ( i ); } Explanation i is initialized with 1. The loop runs while i <= 5. When i becomes 2, continue skips the current iteration, so 2 is not printed. When i becomes 4, break stops the loop immediately, so 4 and the remaining values are not printed. Only 1 and 3 are printed. Output 1 3 What is Looping? And why do we use it? Loops are used to execute a block of code repeatedly without writing the same code multiple times. They help reduce code repetition and make programs more efficient. example: without looping: console . log ( 1 ); console . log ( 2 ); console . log ( 3 ); console . log ( 4 ); console . log ( 5 ); with looping: for loop Syntax for ( initialization ; condition ; increment ){ // code } for ( let i = 1 ; i <= 5 ; i ++ ){ console . log ( i ); } This also gives me the same output, but the code is reduced to be smart. output is: 1 2 3 4 5 Print Numbers from 5 to 1 for ( let i = 5 ; i >= 1 ; i -- ){ console . log ( i ); } Explanation i is initialized with 5. The loop runs while i >= 1. console.log(i) prints the current value of i. i-- decreases the value by 1 after each iteration. When i becomes 0, the condition 0 >= 1 is false, so the loop stops. Output 5 4 3 2 1 Expected Output 1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz program for ( let a = 1 ; a <= 10 ; a ++ ) { if ( a % 3 == 0 ) { console . log ( " Fizz " ); } else if ( a % 5 == 0 ) { console . log ( " Buzz " ); } else { console . log ( a ); } } Explanation a is initialized with 1. The loop runs while a <= 10. If a is divisible by 3, it prints "Fizz". Else if a is divisible by 5, it prints "Buzz". Otherwise, it prints the number. After each iteration, a++ increases the value by 1. The loop stops when a becomes 11 because the condition 11 <= 10 is false. output 1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz Print Odd Numbers Using continue Expected Output 1 3 5 7 9 Program for ( let i = 1 ; i <= 10 ; i ++ ) { if ( i % 2 == 0 ) { continue ; } console . log ( i ); } Explanation i is initialized with 1. The loop runs while i <= 10. If i is an even number, continue skips the current iteration. Only odd numbers reach console.log(i). After each iteration, i++ increases the value by 1. The loop stops when i becomes 11 because the condition 11 <= 10 is false. Output 1 3 5 7 9 Expected Output 1 2 3 4 5 program for ( let i = 1 ; i <= 10 ; i ++ ) { if ( i == 6 ) { break ; } console . log ( i ); } Explanation i is initialized with 1. The loop runs while i <= 10. When i becomes 6, the break statement stops the loop immediately. Since the loop stops before console.log(i), 6 is not printed. The loop ends without checking the remaining values. Output 1 2 3 4 5 Expected Output 1 3 program for ( let i = 1 ; i <= 5 ; i ++ ) { if ( i === 2 ) { continue ; } if ( i === 4 ) { break ; } console . log ( i ); } Explanation i is initialized with 1. The loop runs while i <= 5. When i becomes 2, continue skips the current iteration, so 2 is not printed. When i becomes 4, break stops the loop immediately, so 4 and the remaining values are not printed. Only 1 and 3 are printed. Output 1 3