Iterative Constructs in Java (Loops) — ICSE Class 10 Computer Applications

for (int i = 1; i <= 5; i++)
{
    System.out.print(i + " ");
}
System.out.println();
System.out.println("Loop over");

Output:

1 2 3 4 5 
Loop over

Condition i <= 5 chhathi baar (i = 6) false ho jaati hai, isliye loop wahin ruk jaata hai. Body paanch baar chali.

int n = 5, f = 1;
for (int i = 1; i <= n; i++) f = f * i;
System.out.println("Factorial of " + n + " = " + f);

Output:

Factorial of 5 = 120

Yeh for ka classic case hai — kitni baar chalna hai (n baar) pehle se pata hai. Ek hi cheez ka dhyaan rakho: f ki initial value 1 honi chahiye, 0 nahi, warna sab kuch 0 ho jaayega.

int i = 1, sum = 0;
while (i <= 10)
{
    sum = sum + i;
    i++;
}
System.out.println("Sum of 1 to 10 = " + sum);
System.out.println("i after loop = " + i);

Output:

Sum of 1 to 10 = 55
i after loop = 11

Dhyaan do: i loop ke baad 11 hai, 10 nahi. Yeh exactly wahi cheez hai jo examiner “value of i after the loop” wale question mein test karta hai.

int m = 1234, rev = 0;
while (m > 0)
{
    int d = m % 10;
    rev = rev * 10 + d;
    m = m / 10;
}
System.out.println("Reverse of 1234 = " + rev);

Output:

Reverse of 1234 = 4321

Yeh while ka canonical example hai: number mein kitne digits hain, yeh pehle se pata nahi — bas “jab tak m bacha hai” chalte raho. Digit nikalne ka jodi-formula yaad kar lo: % 10 se aakhri digit milta hai, / 10 se woh hata deta hai, aur rev * 10 + d use nayi jagah jodta hai. Palindrome aur Armstrong dono programs isi par khade hain.

int i = 11;
while (i <= 10)
{
    System.out.println("while body: " + i);
    i++;
}

int j = 11;
do
{
    System.out.println("do-while body: " + j);
    j++;
}
while (j <= 10);

Output:

do-while body: 11

Yehi poora output hai. while ka body ek baar bhi nahi chala (11 <= 10 shuru se hi false tha), par do…while ka ek baar chal gaya. Yeh 2-mark ka pakka question hai — isse dohra lo.

System.out.println("--- for ---");
for (int i = 1; i <= 3; i++) System.out.print(i + " ");
System.out.println();

System.out.println("--- while ---");
int i = 1;
while (i <= 3) { System.out.print(i + " "); i++; }
System.out.println();

System.out.println("--- do while ---");
int k = 1;
do { System.out.print(k + " "); k++; } while (k <= 3);
System.out.println();

Output:

--- for ---
1 2 3 
--- while ---
1 2 3 
--- do while ---
1 2 3 

Teeno ka output bilkul same. Conversion ka rule: initialization loop se pehle, condition apni jagah, updation body ke akhir mein.

for (int i = 1; i <= 10; i++)
{
    if (i == 6) break;
    if (i % 2 == 0) continue;
    System.out.print(i + " ");
}
System.out.println();

Output:

1 3 5 

i = 2 aur 4 par continue ne print skip karwaya, par loop chalta raha. i = 6 par break ne loop hi khatam kar diya — 7, 8, 9, 10 tak baat hi nahi pahunchi.

for (int i = 5; i >= 1; i--)
{
    if (i == 3) continue;
    System.out.print(i);
}
System.out.println();

Output:

5421

Sirf 3 gayab hai. Aur dhyaan do — for loop mein continue ke baad bhi i-- chalta hai, isliye loop atakta nahi.

for (int i = 1, j = 10; i < j; i++, j--)
{
    System.out.println(i + " ... " + j);
}

Output:

1 ... 10
2 ... 9
3 ... 8
4 ... 7
5 ... 6

Ek counter upar, doosra neeche — jab woh mil jaate hain, loop ruk jaata hai. Comma se dono ko initialize aur update kiya jaata hai.

int i = 1;
for ( ; i <= 3; )
{
    System.out.print(i + " ");
    i++;
}
System.out.println("| i = " + i);

Output:

1 2 3 | i = 4

for ke teeno khaane khaali chhode ja sakte hain — semicolons phir bhi zaroori hain. Yahan i loop ke bahar declare hua, isliye loop ke baad bhi use kar sakte hain.

for (int i = 1; i <= 4; i++)
{
    for (int j = 1; j <= 5; j++)
    {
        System.out.print("* ");
    }
    System.out.println();
}

Output:

* * * * * 
* * * * * 
* * * * * 
* * * * * 

Andar wala loop har row mein 5 stars chhaapta hai; System.out.println() bahar wale loop mein hai, isliye har row ke baad line badalti hai.

for (int i = 1; i <= 5; i++)
{
    for (int j = 1; j <= i; j++)
    {
        System.out.print(j + " ");
    }
    System.out.println();
}

Output:

1 
1 2 
1 2 3 
1 2 3 4 
1 2 3 4 5 

Poora triangle ek hi cheez se banta hai: andar wale loop ki condition j <= i hai, koi fixed number nahi. Har naye row par i bada hota hai, isliye row lambi hoti jaati hai.

for (int i = 1; i <= 4; i++)
{
    for (int j = 4; j > i; j--) System.out.print(" ");
    for (int j = 1; j <= i; j++) System.out.print("*");
    System.out.println();
}

Output:

   *
  **
 ***
****

Do inner loops: pehla spaces chhaapta hai, doosra stars. Yeh pattern questions ka master template hai — “kitne spaces, kitne stars” bas yeh do sawaal poochho.