This is for C++: Using a nested for loop output the following pattern to the screen: A
AB
ABC
ABCD
ABCDE
ABCDEF
ABCDEFG
ABCDEFGH
ABCDEFGHI
ABCDEFGHIJ
ABCDEFGHIJK
ABCDEFGHIJKL
ABCDEFGHIJKLM
ABCDEFGHIJKLMN
ABCDEFGHIJKLMNO
ABCDEFGHIJKLMNOP
ABCDEFGHIJKLMNOPQ
ABCDEFGHIJKLMNOPQR
ABCDEFGHIJKLMNOPQRS
ABCDEFGHIJKLMNOPQRST
ABCDEFGHIJKLMNOPQRSTU
ABCDEFGHIJKLMNOPQRSTUV
ABCDEFGHIJKLMNOPQRSTUVW
ABCDEFGHIJKLMNOPQRSTUVWX

Following are the code to the given question:

#include <iostream>//header file

using namespace std;

int main()//main method

{

int r=26,x,y;//defining integer variable  

char c;//defining a character variable

for(x= 1; y<= r; x++)//using for loop for count value

{

for(y= 1; y<= x; y++)//using for loop to convert value in triangle  

{

c=(char)(y+64);//convert value into character  

cout << c;//print character value

}

cout << "\n";//use print method for line break

}

return 0;

}

Output:

Please find the attachment file.

Explanation:

In this code, three integer variable "x,y, and r", and one character variable "c" is declared, that is used in the nested for loop,  in the first for loop it counts the character value and in the next for loop, it converts the value into a triangle and uses the char variable to print its character value.