大佬求带，为什么程序显示无法从b中读取数据

#include<cstdio>
using namespace std;
int main() {
	long long a[25][25];
	long long b[25][25];
	int c, d, e, f;
	scanf("%d %d %d %d", &e, &f, &c, &d);
	a[c][d] = 1;
	if (c > 1 && d != 0) a[c - 2][d - 1] = 1;
	if (c > 1 && d != 20) a[c - 2][d + 1] = 1;
	if (c < 19 && d != 0) a[c + 2][d - 1] = 1;
	if (c <19 && d != 20) a[c + 2][d + 1] = 1;
	if (c != 0 && d > 1) a[c - 1][d - 2] = 1;
	if (c != 0 && d != 20) a[c - 1][d + 2] = 1;
	if (c != 20 && d > 1) a[c + 1][d - 2] = 1;
	if (c != 20 && d < 19) a[c + 1][d + 2] = 1;
	for (int i = 0; i < e; i++) {
		for (int k = 0; k < f; k++) {
			if (a[i][k] != 1) {
				if (i == 0 && k == 0) 
					b[0][0] = 1;
				else if (i == 0 && k != 0) 
					b[0][k] = b[0][k-1]; 
				else if (i != 0 && k == 0) 
					b[i][0] = b[i - 1][0];
				else  
					b[i][k] = b[i - 1][k]+b[i][k-1];
			}
		}
	}
	printf("%lld\n", b[e][f]);
	return 0;
}