Alright, let's figure out how to print this specific 10-line triangle pattern in C—we'll break it down step by step so you understand exactly what's going on.

First, here's the pattern we're targeting:

1
12A
123BA
1234CBA
12345DCBA
123456EDCBA
1234567FEDCBA
12345678GFEDCBA
123456789HGFEDCBA
12345678910IHGFEDCBA

Pattern Breakdown #

Let's dissect each line to spot the repeating rules:

• For the n-th line (starting at 1 and going up to 10):
  1. The first part counts sequentially from 1 to n. A nice thing here is that when n hits 10, we just print the full number—no special handling needed for two-digit values.
  2. The second part is a reverse alphabet sequence, starting from the (n-1)-th uppercase letter and going back to 'A'. For example:
     • Line 2 (n=2): Only 'A' (since 2-1=1, which is the first letter in the alphabet)
     • Line 3 (n=3): 'B' followed by 'A' (3-1=2, the second letter is B)
     • Line 10 (n=10): 'I' all the way down to 'A' (10-1=9, the ninth letter is I)

Complete C Code #

#include <stdio.h>

int main() {
    const int total_lines = 10; // We're making this a constant for clarity
    
    // Loop through each line from 1 to 10
    for (int line = 1; line <= total_lines; line++) {
        // Print the increasing number sequence (1 to current line number)
        for (int num = 1; num <= line; num++) {
            printf("%d", num);
        }
        
        // Calculate the starting letter for the reverse alphabet segment
        // For line 1, this will be a character before 'A', so the loop won't run
        char start_letter = 'A' + (line - 2);
        
        // Print letters from start_letter down to 'A'
        for (char c = start_letter; c >= 'A'; c--) {
            printf("%c", c);
        }
        
        // Move to the next line after finishing the current one
        printf("\n");
    }
    
    return 0;
}

How This Code Works #

Let's walk through each part to demystify it:

1. Outer Loop: The for loop runs from 1 to 10, handling each line one by one. Using a const for total_lines makes it easy to adjust the number of lines later if you want.
2. Number Sequence: The inner loop prints numbers from 1 up to the current line number. Since we're using printf("%d"), it automatically handles single-digit (1-9) and two-digit (10) numbers without extra code—handy!
3. Reverse Alphabet Sequence:
   • For line 1: line - 2 is -1, so start_letter becomes 'A' - 1 (a character before 'A'). The loop condition c >= 'A' fails right away, so no letters are printed (perfect, since the first line only has "1").
   • For line 2: start_letter is 'A' + 0 = 'A', so we print just 'A'.
   • For line 10: start_letter is 'A' + 8 = 'I', so we loop from 'I' back to 'A' printing each character.
4. New Line: After each line's numbers and letters are printed, printf("\n") moves us to the next line to start fresh.

Quick Test #

Compile and run this code, and you'll get exactly the pattern you asked for. If you ever want more or fewer lines, just change the value of total_lines—the logic scales perfectly.

内容的提问来源于stack exchange，提问作者Aditya Pandey