求优化：n项1+11+111+...求和C代码，解决扩展性问题

Hey there! The core issue with your current code is that you’re hardcoding each digit’s weight using clunky else if branches, which locks it into only supporting up to 5 terms. Let’s rewrite this to handle any positive integer n while making the code cleaner, more efficient, and way easier to maintain.

Key Improvements We’ll Implement: #

• Dynamically generate each term in the series (no more manual digit-by-digit checks)
• Calculate the sum directly by adding each generated term (no need to break down digits)
• Match the exact output format you need: term1 + term2 + ... followed by the total sum

Optimized Code: #

// Calculate sum of series: 1 + 11 + 111 + ... + n terms
#include <stdio.h>

int main(void) {
    int n;
    long long sum = 0; // Use 64-bit integer to avoid overflow for larger n
    long long current_term = 0;

    printf("Input the number of terms : ");
    scanf("%d", &n);

    for (int i = 1; i <= n; i++) {
        current_term = current_term * 10 + 1; // Generate next term dynamically
        sum += current_term;

        // Handle output formatting to avoid leading " + "
        if (i == 1) {
            printf("%lld", current_term);
        } else {
            printf(" + %lld", current_term);
        }
    }

    printf("\nThe Sum is : %lld\n", sum);
    return 0;
}

Let’s Break Down the Changes: #

1. Dynamic Term Generation:

   • The line current_term = current_term * 10 + 1 is the game-changer. It builds each term incrementally:
     • Iteration 1: 0 * 10 + 1 = 1
     • Iteration 2: 1 * 10 + 1 = 11
     • Iteration 3: 11 * 10 + 1 = 111
     • This works for any n, no hardcoded branches required!

2. Overflow Prevention:

   • We switched to long long for sum and current_term because even for n=10, the sum hits 1234567900—way larger than the maximum value of a 32-bit integer (~2 billion). 64-bit integers let us handle much bigger n without errors.

3. Clean Output Formatting:

   • The conditional print statement ensures we don’t add an extra " + " before the first term, perfectly matching the output style you specified.

Example Output (n=5): #

1 + 11 + 111 + 1111 + 11111
The Sum is : 12345

This code is scalable, readable, and eliminates the messy conditional logic from the original version.

内容的提问来源于stack exchange，提问作者user9295826