给定一个整数数组，求其元素之和

Question

Given an array of integers, find the sum of its elements. my problem is that; in c language you have only fixed size array; my code does not print the sum of random size array which the question demands;[1,2,3,4,5,-------n elements] it prints for only for ex 6 or defnite size aray; using a loop;

#include <stdio.h>
int main() {
    int i;
    scanf("%d\n",&i);
    int a[6];
    int sum=0;
    for(i=0;i<=5;i++)
        scanf("%d\n",&a[i]);
    for(i=0;i<=5;i++)
        sum=sum+a[i];
    printf("%d\n",sum);
    return 0;
}

Answer 1

It seems you want to let you user input the number of elements in the array. Your code scan that information into variable i . Therefore you can't use variable i as counter in the for loops. You need two different variables. One variable to hold the the number of integers to include in the sum and another variable for the loops.

Further to get a variable sized array, you need to use the users input when you define the array. This is called VLA (Variable Length Array).

Something like:

#include <stdio.h>
int main() {
    int i;
    int N = 0;         // New variable holding the number of integers in the sum
    scanf("%d\n",&N);  // scan into N
    int a[N];          // Use N for the VLA
    int sum=0;
    for(i=0;i<N;i++)   // Use N as limit
        scanf("%d\n",&a[i]);
    for(i=0;i<N;i++)   // Use N as limit
        sum=sum+a[i];
    printf("%d\n",sum);
    return 0;
}

That said - be careful about VLAs. If the user inputs a high number for N a stack overflow may occur. If you want to use VLAs your code should enforce a maximum limit for the users input.

It's typically better to use dynamic allocation instead of VLA. Like:

#include <stdio.h>
#include <stdlib.h>
int main() {
    int i;
    int N = 0;
    scanf("%d\n",&N);
    int *a = malloc(N * sizeof *a);  // Dynamic allocation
    if (a == NULL) exit(1);          // Check for allocation failure
    int sum=0;
    for(i=0;i<N;i++)
        scanf("%d\n",&a[i]);
    for(i=0;i<N;i++)
        sum=sum+a[i];
    printf("%d\n",sum);
    free(a);                         // Free allocated memory
    return 0;
}

Some extra comments:

1) To calculate the sum you actually don't need an array. Just scan into some int and add it to sum . No need for storing it in an array first.

2) Always check the return value of scanf . Example: if (scanf("%d\\n",&N) != 1) exit(1);