>>69
#include <stdio.h>

int main()
{
    FILE *fp;
    int a;
    int line = 21; // 行数
    char ch[10];
    if(NULL == (fp = fopen("test.txt", "rb"))) return 0;

    while(fgets(ch,3,fp)){
        sscanf(ch,"%d",&a);
        printf("%d\n",a);
        fseek(fp, line, SEEK_CUR);
    }

    return 0;
}
とりあえず動く