~ no response on stdout ~ in C [closed]

Answer 1

Your problem is in this line:

int a,query,in,n,b[n],sum[a];

What is the meaning of b[n]? And of sum[a]? Assuming that you would like to have a language with magically growing arrays, C is a bad choice.

In C language arrays are a structure with size known at compile time. Anyway, let's assume that your compiler supports the horrible hack of variable-length arrays. You can do this:

#include 
#include 
#include 

int main(void) {
    int a, query, in , n;
    scanf("%d", &query);
    int sum[query+1];

    for (a = 1; a <= query; a++) {
        sum[a] = 0;
        scanf("%d", &in);
        int b[in+1];
        for (n = 1; n <= in ; n++) {
            b[n] = 1 + 7 * (n - 1) + 6 * (n - 1) * (n - 2) + (n - 1) * (n - 2) * (n - 3);
            sum[a] = sum[a] + b[n];
        }
    }

    for (a = 1; a <= query; a++) {
        printf("%d\n", sum[a]);
    }

    return 0;
}

Note the changes: first you need to know the size of the array, then you can allocate it. Moreover, I increased the size of the array in order to support your choice of starting from 1. Lastly I also zeroed the initial value for sum array.