能正确输入，但没有输出是为什么？

int main()

{

char location[100][100];

int x, y, n, m, i, j,sum= -1;

scanf("%d %d", &n, &m);

scanf("%d %d", &x, &y);

for (i=1; i <= n; i++)

{

for (j=1; j <= m; j++)

{

scanf("%s", &location[i][j]);

}

}

while (x <= n && x > 0 && y <= m && y > 0) {

switch (location[x][y]) {

case 'U':

location[x][y] = 'W';

y--;

sum += 1;

break;

case 'D':

location[x][y] = 'W';

y++;

sum += 1;

break;

case 'L':

location[x][y] = 'W';

x--;

sum += 1;

break;

case 'R':

location[x][y] = 'W';

x++;

sum += 1;

break;

default:

break;

}

}

printf("%d", sum);

return 0;

}