C++ Nested Loops

🔁🔁 C++ Nested Loops

Nested Loop ka matlab hota hai ek loop ke andar doosra loop.
Ye zyada tar patterns, tables, matrices, grids ke liye use hota hai.

🔹 1. Syntax

for (initialization; condition; update) {
for (initialization; condition; update) {
// inner loop code
}
}

👉 Outer loop har iteration ke liye inner loop poora chalta hai.

🔹 2. Basic Nested Loop Example

for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 3; j++) {
cout << i << j << " ";
}
}

Output:

11 12 13 21 22 23 31 32 33

🔹 3. Multiplication Table (1 to 3)

for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 10; j++) {
cout << i * j << " ";
}
cout << endl;
}

🔹 4. Pattern Printing Example

⭐ Star Pattern

for (int i = 1; i <= 4; i++) {
for (int j = 1; j <= i; j++) {
cout << "* ";
}
cout << endl;
}

Output:

*
* *
* * *
* * * *

🔹 5. Nested while Loop

int i = 1;

while (i <= 3) {
int j = 1;
while (j <= 3) {
cout << i << j << " ";
j++;
}
cout << endl;
i++;
}

🔹 6. Nested do-while Loop

int i = 1;

do {
int j = 1;
do {
cout << i << j << " ";
j++;
} while (j <= 3);
cout << endl;
i++;
} while (i <= 3);

🔹 7. Loop Iteration Count (Important)

for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 3; j++) {
// Total iterations = 3 × 3 = 9
}
}

❌ Common Mistakes

for (int i = 1; i <= 3; i++) {
for (int i = 1; i <= 3; i++) { // ❌ same variable name
cout << i;
}
}

✔ Correct:

for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 3; j++) {
cout << j;
}
}

📌 Summary

  • Nested loops = loop inside loop

  • Inner loop completes fully for each outer loop

  • Used in patterns, tables, matrices

  • Time complexity increases (O(n²))

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