Printing number pattern examples using For Loop in C++

A nested for loop is a loop inside another loop. The outer loop is executed first, followed by the inner loop. The inner loop is executed completely for each iteration of the outer loop. Here's the general structure of a nested for loop:

Syntax:
       for( initial ; Condition ; increment / decrement )  // Outer Loop Statements
       {
                for( initial ; Condition ; increment / decrement )  // Inner Loop Statements
                {
                       // code block to be executed
                }
       }

In this loop, the outer loop runs first and initializes a counter variable. The outer loop also has a condition that is checked before each iteration. If the condition is true, the inner loop is executed. The inner loop also has a counter variable, a condition, and an update statement. The code block inside the inner loop is executed for each iteration of the inner loop.

This program prints a pattern of numbers in a triangle shape. The input value a is the number of rows in the triangle. Here is how the program works:

  • The program starts by declaring three variables: i, j, and a.
  • The user is prompted to enter a value for a.
  • The program enters a loop that iterates i from 1 to a. This loop controls the number of rows in the triangle.
  • Inside the i loop, the program enters another loop that iterates j from 1 to i. This loop controls the number of numbers in each row of the triangle.
  • Inside the j loop, the program prints the value of i for each iteration of j. This ensures that the numbers in each row of the triangle increase by 1.
  • After the j loop finishes, the program prints a newline character to move to the next row of the triangle.
  • The program repeats steps 4-6 until the i loop finishes.
#include<iostream>
using namespace std;
int main()
{
    int i,j,a;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=1;j<=i;j++)
        {
            cout<<i;
        }
    }
    return 0;
}
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Output

Enter the value:5
1
22
333
4444
55555

Source Code Example : 2

#include<iostream>
using namespace std;
int main()
{
    int i,j,a;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=1;j<=i;j++)
        {
            cout<<j;
        }
    }
    return 0;
}
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Output

Enter the value:5
1
12
123
1234
12345

Source Code Example : 3

#include<iostream>
using namespace std;
int main()
{
    int i,j,a,b=1;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=1;j<=i;j++)
        {
            cout<<" "<<b;
            b++;
        }
    }
    return 0;
}
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Output

Enter the value:5
 1
 2 3
 4 5 6
 7 8 9 10
 11 12 13 14 15

Source Code Example : 4

#include<iostream>
using namespace std;
int main()
{
    int i,j,a;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=1;j<=i;j++)
        {
            cout<<(i-j+1);
        }
    }
    return 0;
}
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Output

Enter the value:10
Enter the value:5
1
21
321
4321
54321

Source Code Example : 5

#include<iostream>
using namespace std;
int main()
{
    int i,j,a;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=1;j<=(a-i);j++)
        {
            cout<<" ";
        }
        for(j=1;j<=i;j++)
        {
            cout<<j;
        }
    }
    return 0;
}
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Output

Enter the value:5
    1
   12
  123
 1234
12345

Source Code Example : 6

#include<iostream>
using namespace std;
int main()
{
    int i,j,a;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=a-i+1;j>0;j--)
        {
            cout<<j;
        }
    }
    return 0;
}
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Output

Enter the value:5
54321
4321
321
21
1

Source Code Example : 7

#include<iostream>
using namespace std;
int main()
{
    int i,j,a;
    cout<<"\nEnter the value:";
    cin>>a;
    for(i=1;i<=a;i++)
    {
        cout<<"\n";
        for(j=1;j<=i;j++)
        {
            cout<<" ";
        }
        for(j=1;j<=(a-i+1);j++)
        {
            cout<<j;
        }
    }
    return 0;
}
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Output

Enter the value:6
123456
  12345
   1234
    123
     12
      1

Source Code Example : 8

#include<iostream>
using namespace std;
int main()
{
    int i,j,n;
    cout<<"\nEnter the value :";
    cin>>n;
    for(i=1;i<=n;i++)
    {
        cout<<"\n";
        for(j=1;j<=(n-i);j++)
        {
            cout<<"  ";
        }
        for(j=1;j<=i;j++)
        {
            cout<<" "<<j;
        }
        for(j=1;j<i;j++)
        {
            cout<<" "<<(i-j);
        }
    }
    for(i=1;i<=n;i++)
    {
        cout<<"\n";
        for(j=1;j<=i;j++)
        {
            cout<<"  ";
        }
        for(j=1;j<(n-i);j++)
        {
            cout<<" "<<j;
        }
        for(j=(n-i);j>0;j--)
        {
            cout<<" "<<j;
        }
    }
    return 0;
}
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Output

Enter the value :5
         1
       1 2 1
     1 2 3 2 1
   1 2 3 4 3 2 1
 1 2 3 4 5 4 3 2 1
   1 2 3 4 3 2 1
     1 2 3 2 1
       1 2 1
         1

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