how to use nested for loop for getting following output: 5,4,3,2,1 5,4,3,2 5,4,3 5,4 5

Answer 1

At least indicate the language you refer to in "Relevant Tags" section. In C or C++ the following main function will work.

int main()
{
int size = 5;

for(int row = size; row; row--)
for(int col = 0; col < row; col++)
printf("%d%c", size - col, (col < row - 1 ? ',' : '\n'));

return 0;
}

Answer 2

in C would do this:

#include <stdio.h>

int main(){
int cont = 1;

for(int i = 0; i < 5; i++){
for(int a = 5; a >= cont; a--){
printf("%d", a);
}
printf("\n");
cont++;
}
}

Answer 3

Which language do you want it in?

In c++ I would do this:
int num = 5;
for (int i=num; i>0; i--) {
for (int j=num; j>num-i; j--) {
cout << j;
}
cout << endl;
}