Learning c

Now learning c, I wrote three programs today. Any program is easy for me because it is for beginner. I am learning to refers "初心者のためのポイント学習Ｃ言語", my target is to understand about c and I wanna be engineer looks like graduate of computer science. In the future,I will learning as much as possible

#include <stdio.h>

int main(void){

  int i;
  int j;

  for(i = 0;i<10;i++){
    for(j = 0;j<=i;j++){
      printf("%d",j);
    }
    printf("\n");
  }
return 0;
}

#include <stdio.h>

int main(void){

  int data1 = 1000;
  int data2;
  do{
    printf("整数値を入力");
    scanf("%d",&data2);
    data1 = data1 - data2;
    printf("data1=%d\n",data1);

  }while(data1>0);

  return 0;
}

#include <stdio.h>

int main(void){

  char str1[80];
  char str2[80];
  printf("文字列入力");
  scanf("%s",str1);
  int i = 0;
  do{
    str2[i] = str1[i];

  }while(str1[i++]!='\0');
  printf("str2 = %s\n",str2);

  return 0;
}