#include <stdio.h> static int a = 10; static int b = 20; int add(int a,int b) { int c; scanf("%d", &c); if (a + b == c) return 1; return 0; } void output(int k) { if (k) printf("Right!\n"); else { printf("Not correct! Try again!\n"); output(add(a, b)); } } main() { printf("%d+%d=", a, b); output(add(a, b)); }