Producing a pyramid of capital letters

Question

Now I'm reading C Premier Plus by Stephen Prata and there's an exercise 4 in chapter 6 which has no solution in the book, so I can't check if I did it properly. My code works like it should, but I want to know maybe there are some better or cleaner solutions.

Here's the description:

Have a program request the user to enter an uppercase letter. Use nested loops to produce a pyramid pattern like this:

    A
   ABA
  ABCBA
 ABCDCBA
ABCDEDCBA

The pattern should extend to the character entered. For example, the preceding pattern would result from an input value of E .

Hint: Use an outer loop to handle the rows. Use three inner loops in a row, one to handle the spaces, one for printing letters in ascending order, and one for printing letters in descending order.

#include <stdio.h>

int main(void) {
    char ch;
    char row;
    char spaces;
    char let;
    char back;

    printf("Please, insert an uppercase letter: ");
        scanf("%c", &ch);

    for(row = 'A'; row <= ch; row++) {
        for(spaces = ch; spaces > row; spaces--)
            printf(" ");

        for(let = 'A'; let < row; let++)
            printf("%c", let);    

        for(back = let; back >= 'A'; back--)
            printf("%c", back);
        printf("\n");
    }
    return 0;
}

Answer 1

It's been a while since I coded in C but here are couple observations.

• Input validation. You should check if the scanned character is really an upper case letter or exit with an error otherwise.
• Choice of functions. Since you're scanning and printing out a character at a time, you could have used putchar instead of printf, and getchar instead of scanf.
• Variable naming. let is not the best variable name since it is often used as a keyword in other languages. You also could have used the same variable in place of let and back.
• Code formatting. There are a lot of different opinions about how to format source code, but most agree that it is better to put parenthesis around loop and condition bodies.

Here is how I would have formatted your code.

#include <stdio.h>

int main(void) {
    char ch;
    char row;
    char spaces;
    char letter;

    printf("Please, insert an uppercase letter: ");
    scanf("%c", &ch);

    for (row = 'A'; row <= ch; row++) {
        for (spaces = ch; spaces > row; spaces--) {
            printf(" ");
        }
        for (letter = 'A'; letter < row; letter++) {
            printf("%c", letter);    
        }
        for (; letter >= 'A'; letter--) {
            printf("%c", letter);
        }
        printf("\n");
    }
    return 0;
}