创建文件用c语言编写

已解答并且已结题，辛苦两位的帮助，作为大一新生刚刚接触c语言不懂如何编写程序，尤其是这个指针环节很难

#include <stdio.h>
#include<string.h>
int main()
{
    int i,j=0,k=0,l=0,a1[30]={25,44,1,-27,-119,31,-13,0,23,17,101,-2,324,-7,-39};
    int a2[30],a3[30],a4[30];
    for(i=0;i<15;i++){
        if(a1[i]>20 || -1*a1[i]>20 ){
            a2[j++]=a1[i];
        }
    }
     for(i=0;i<15;i++){
        if(a1[i]<0 && -a1[i]%2==1 ){
            a3[k++]=a1[i];
        }
    }
    for(i=0;i<15;i++){
        if(a1[i]%4==0 ){
            a4[l++]=a1[i];
        }
    }
    FILE *fp;
    fp = fopen("123456.txt","w+");
    for(i=0;i<15;i++){
        fprintf(fp,"%d ",a1[i]);
    }
    fprintf(fp,"\n");
    for(i=0;i<j;i++){
        fprintf(fp,"%d ",a2[i]);
    }
    fprintf(fp,"\n");
    for(i=0;i<k;i++){
        fprintf(fp,"%d ",a3[i]);
    }
    fprintf(fp,"\n");
    for(i=0;i<l;i++){
        fprintf(fp,"%d ",a4[i]);
    }
    fprintf(fp,"\n");
    fclose(fp);

}

#include<stdio.h>
int main()
{
    int a[]={25,44,1,-27,-119,31,-13,0,23,17,101,-2,324,-7,-39};
    int b[15],c[15],d[15];
    int bc=0,cc=0,dc=0,i;
    FILE *f;
    for(i=0;i<15;i++)
    {
        if(abs(a[i])>20)
            b[bc++]=a[i];
        if(a[i]<0 && a[i]%2)
            c[cc++]=a[i];
        if(a[i]%4==0)
            d[dc++]=a[i];
    }
    f=fopen("123456.txt","w+");
    for(i=0;i<15;i++)
        fprintf(f,"%d ",a[i]);
    fprintf(f,"\n");
    for(i=0;i<bc;i++)
        fprintf(f,"%d ",b[i]);
    fprintf(f,"\n");
    for(i=0;i<cc;i++)
        fprintf(f,"%d ",c[i]);
    fprintf(f,"\n");
    for(i=0;i<dc;i++)
        fprintf(f,"%d ",d[i]);
    fprintf(f,"\n");
    fclose(a);
}

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