求助：使用scanf输入整数后C程序崩溃问题

Hey there! Let's dig into why your polynomial program is crashing after inputting integers. First, let's start with the code snippet you shared, then walk through the most likely culprits for this kind of crash.

Your Shared Code Snippet #

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "Homework.h"
#include "Fraction.h"

int main() {
    //Input from user
    int degree, i;
    printf("Insert the degree of the polynomial: \n");
    scanf("%d", &degree);
    //Get t...
}

Common Causes for the Crash #

Since your code cuts off right after getting the degree, here are the most frequent issues that lead to crashes in polynomial implementations like this:

• Incorrect Dynamic Memory Allocation
  If your polynomial uses a dynamic array (e.g., Fraction* coefficients = malloc(sizeof(Fraction) * (degree + 1))) to store coefficients, there are two easy mistakes here:

  1. You forgot that a degree-n polynomial has n+1 coefficients (from the constant term up to x^n). Using just degree instead of degree+1 will leave you short on memory, causing out-of-bounds access.
  2. You didn't check if malloc failed. If memory allocation returns NULL, trying to write to that pointer will immediately crash your program. Always add a check:

     Fraction* coeffs = malloc(sizeof(Fraction) * (degree + 1));
     if (coeffs == NULL) {
         fprintf(stderr, "Failed to allocate memory!\n");
         return 1;
     }
     

• Unvalidated Input
  If the user enters something that's not an integer (like a string or decimal), scanf will fail to update degree, leaving it with a garbage value. Using this garbage value to allocate memory or run loops will lead to unpredictable behavior (and crashes). Add input validation:

  if (scanf("%d", &degree) != 1 || degree < 0) {
      fprintf(stderr, "Please enter a non-negative integer for the degree!\n");
      return 1;
  }
  

• Issues with the Fraction Type
  If your Fraction struct has uninitialized members, or if you're performing operations (like assignment, copying, or destruction) that have memory bugs (e.g., double-freeing pointers inside Fraction), this could cause crashes when you start creating or assigning coefficients for your polynomial.

• Loop Boundary Errors
  When you loop to input coefficients, make sure your loop runs exactly degree + 1 times. A loop like for (i = 0; i < degree; i++) will miss the constant term, while an overextended loop will go out of bounds and crash the program.

Next Steps #

To pinpoint the exact issue, could you share:

• The rest of the main function (especially where you input coefficients and interact with the polynomial)
• The definition of your polynomial struct from Homework.h
• Any functions related to creating, initializing, or destroying polynomials

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