C++ Nested Loops - C++ Tutorial

In C++, you can place one loop inside another. This is known as a nested loop. Nested loops are especially useful for working with multi-layered structures like tables, matrices, or multi-dimensional arrays.

How Nested Loops Work

In a nested loop setup:

The outer loop controls the overall iterations.
For each iteration of the outer loop, the inner loop runs its entire sequence.

Syntax

for (initialization; condition; update) {  
    for (initialization; condition; update) {  
        // Code to execute in inner loop  
    }  
}

C++
​x
 
for (initialization; condition; update) {      for (initialization; condition; update) {          // Code to execute in inner loop      }  }​

Example: Showing Motorcycle Brands and Models

#include <iostream>
using namespace std;

int main() {
    for (int brandIndex = 1; brandIndex <= 2; ++brandIndex) {  // Outer loop (brands)
        cout << "Brand: " << brandIndex << "\n";
        for (int modelIndex = 1; modelIndex <= 3; ++modelIndex) {  // Inner loop (models)
            cout << " Model: " << modelIndex << "\n";
        }
    }

    return 0;
}

C++
 
#include <iostream>using namespace std;​int main() {    for (int brandIndex = 1; brandIndex <= 2; ++brandIndex) {  // Outer loop (brands)        cout << "Brand: " << brandIndex << "\n";        for (int modelIndex = 1; modelIndex <= 3; ++modelIndex) {  // Inner loop (models)            cout << " Model: " << modelIndex << "\n";        }    }​    return 0;}​

Explanation

The outer loop (brandIndex) iterates twice, representing two brands.
The inner loop (modelIndex) runs three times for each brand.
Together, the nested loop produces six outputs—three models for each of two brands.

Output:

Brand: 1  
 Model: 1  
 Model: 2  
 Model: 3  
Brand: 2  
 Model: 1  
 Model: 2  
 Model: 3

C++
 
Brand: 1   Model: 1   Model: 2   Model: 3  Brand: 2   Model: 1   Model: 2   Model: 3  ​

Example: Generating a Grid of Bike IDs

Nested loops can also create patterns, grids, or formatted outputs.

#include <iostream>
using namespace std;

int main() {
    for (int row = 1; row <= 2; ++row) {  // Outer loop (rows)
        for (int column = 1; column <= 3; ++column) {  // Inner loop (columns)
            cout << "BikeID[" << row << "," << column << "] ";
        }
        cout << "\n";
    }

    return 0;
}

C++
 
#include <iostream>using namespace std;​int main() {    for (int row = 1; row <= 2; ++row) {  // Outer loop (rows)        for (int column = 1; column <= 3; ++column) {  // Inner loop (columns)            cout << "BikeID[" << row << "," << column << "] ";        }        cout << "\n";    }​    return 0;}​

How It Works

The outer loop (row) controls the rows (2 iterations).
The inner loop (column) generates the columns (3 iterations per row)

Output:

BikeID[1,1] BikeID[1,2] BikeID[1,3]  
BikeID[2,1] BikeID[2,2] BikeID[2,3]

C++
 
BikeID[1,1] BikeID[1,2] BikeID[1,3]  BikeID[2,1] BikeID[2,2] BikeID[2,3]  ​