下面程序是判断字符串sub是否是字符串st的子串。若是则打印sub在st中首次出现的下标否则打印-1。改正下面程序的错误#include stdioh#include stdlibh main char st50sub30; int ijkkey; printfEnter a string; getsst;

改正后程序如下：

#include <stdio.h> #include <stdlib.h>

int main() { char st[50], sub[30]; int i, j, k, key; printf("Enter a string:"); gets(st); printf("\nEnter a sub string: "); gets(sub); key = 0; for (i = 0; st[i] != '\0'; i++) { for (j = i, k = 0; sub[k] != '\0' && sub[k] == st[j]; j++, k++); if (sub[k] == '\0') { printf("%d", i); key = 1; break; } } if (!key) { printf("-1\n"); } system("pause"); return 0; }