/* File name 4-4.c */ #include <stdio.h> #define BUFFSIZE 1024 unsigned long sum(long n); main() { int n; char nyuryoku[BUFFSIZE]; printf("Input a positive integer.>> "); fgets(nyuryoku, BUFFSIZE, stdin); sscanf(nyuryoku, "%d", &n); printf("The sum of 1 to %d is %d .\n", n, sum(n)); } unsigned long sum(long n) { if ( n==1 ) return 1; else return sum(n-1)+n; }