数据结构学习（一）字符串截取的C语言实现

#include <stdio.h>

int main(){
    int i, j, length;
    char a[] ="hello world";  
    int from, num;

    scanf("%d",&from); //截取开始的字符下标
    scanf("%d",&num); //共截取的字符数
    char b[num];
 
    for (length = 0; a[length]!= '\0'; length++){}
      if (from>=0)
    	if (from+num <= length ){
           i = from; j=0;
           while ( j<num){
           	       b[j] = a[i]; 
           	       printf("%c",b[j]);  
           	       j++; i++;}
    	}return 0;
}