排序，檔案輸入輸出

編寫兩個檔案合併程式，將兩個檔案中的數字重新排序，兩個檔案裡的數字是有序的，輸出到第三個檔案中。

#include<stdio.h>  
const int N = 1e5+5;
int a[N],b[N],res[N*2]; 
int main(){ 
    freopen("ina.txt", "r", stdin);  
    int lena = 0;
	while(scanf("%d",&a[lena])!=EOF) 
		lena++;
		
	freopen("inb.txt", "r", stdin); 
	int lenb = 0;
	while(scanf("%d",&b[lenb])!=EOF) 
		lenb++;
		
	int  posres = 0 ,posa = 0, posb = 0;
	freopen("out.txt","w",stdout);
	while( posa<lena && posb<lenb ){
		if(a[posa]<b[posb]){
			printf("%d ",a[posa]);
			posa++;
		}
		else{
			printf("%d ",b[posb]);
			posb++;
		}
	}
	while( posa<lena ) printf("%d ",a[posa++]);
	while( posb<lenb ) printf("%d ",b[posb++]);
	
    fclose(stdin); 
    fclose(stdout); 
    return 0;
}

檔案的輸入輸出可以看這個
https://blog.csdn.net/weixin_43202635/article/details/97923608
和
https://baike.baidu.com/item/freopen/10942366?fr=aladdin