如何在 C 中的嵌套 for 循环构造中处理 printf？

Question

I need to implement a function using nested for loops in C.

The function has the following declaration:

void nest_loop(int n);

and should print the following for the value n = 5

A B C D E
  A B C D
    A B C
      A B
        A

However I need to implement the function so it produces output for any unsigned int n from the following Intervall [0,9]

In the case of n = 5

From my understanding there are 5 for loops.

for_loop1 prints 5 times the char 'A'

for_loop2 prints 4 times the char 'B'

for_loop3 prints 3 times the char 'C'

for_loop4 prints 2 times the char 'D'

for_loop5 prints 1 time the char 'E'

Also from my understanding the nested loop construct should look something like this:

int n = 5;
int c = n - 1;

for(int i = c ; i < 0; i--){ // loop for 'E'
  c--;
  for(int j = c; j < 0; j--){ // loop for 'D'
    c--;
   for(int k = c; k < 0; k--){ // loop for 'C'
     c--;
    for(int l = c; l < 0; l--){ // loop for 'B'
      c--;
     for(int p = c; p < 0; p--){ // loop for 'A'
     }
    }
   }
  }
}

Is my nested for loop construct correct? If yes, then how do I now implement printf to produce the output mentioned?

Answer 1

As explained by @Jonathon Reinhart, you only need two loops in a construct similar to:

for (int i = n; i > 0; i--) {
  for (int j = 0; j <= i; j++) {
    [...]
  }
}

Answer 2

You know in book also we write left to right not top to bottom so your understanding is wrong above about your loops. Feel free to ask any clarifications thank you.

 #include<stdio.h>
    void nest_loop(int n)
    {
        int i,j;
        char k = 'A';
        for(i=n;i>0;i--)
        {
            for(j=n;j>i;j--)
            {
                printf(" ");//print required spaces.
            }
            for(j=0;j<i;j++)
            {
                printf("%c",k+j);//initial char value of k is A and will be incremented by one as looping continues.
            }
            printf("\n");
        }
    }
    int main()
    {
        int n;
        printf("Enter the row number\n");
        scanf("%d",&n);
        nest_loop(n);
        return 0;
    }

Answer 3

Here is the functional code.

#include <stdio.h>
#include <ctype.h>

void nest_loop(int n) {
    for(int i = 0; i < n; i++){
        for (int j = 0; j < i; j++)
            printf("  ");
        char init_char = 'A';
        for(int j = 0; j < n-i; j++, init_char++)
            printf("%c ", init_char);
        printf("\n");
    }
}

int main()
{
    int num;
    printf("input number: ");
    scanf("%d", &num);
    nest_loop(num);
    return 0;
}

The output is

input number: 5
A B C D E 
  A B C D 
    A B C 
      A B 
        A 

Answer 4

Here you have functional code for your purpose

#include <stdio.h>
#include <ctype.h>

int main()
{
    int num;
    scanf("%d", &num);
    char init_char = 'A';

    for(int i = 0; i < num; i++, init_char++){
        for(int j = num; j > i; j--)
            printf("%c", init_char);
        printf("\n");
    }

        return 0;
}

the answer is well explained in comments, good luck :) *I'd add that in C language you can also increment chars, read what is ASCII table and how chars are encoded as numbers