求n个数中r个数的全部组合问题

#include "stdio.h" #define inFileName "input.txt" #define outFileName "output.txt" int M,N; FILE *fp; int p,q,r; int PaiXu(int M,int N){ while(M>=N){ for() fprintf(fp,"%d ",M); fprintf(fp,"%d ") } PaiXu(M,N); return 0; } void main(){ if((fp=fopen(inFileName,"r"))==NULL){ printf("input.txt not exits!"); } fscanf(fp,"%d\n%d\n",&M,&N); fclose(fp); PaiXu(M,N); fp=fopen(outFileName,"w"); }