好兄弟，这玩意怎么证明的知道吗？我菜狗只能用递归

it means your code is wrong:

• it has undefined behavior if either full_text or search_text are empty
• it is incorrect in other cases, e.g. it returns 0 for "baa", "aa", false
• (it is extremely inefficient to call strlen() in a loop)

This usually means your code performs division by 0, but its difficult to tell without seeing your code.

Is these something wrong?, C language, No 'm' or 'M' in the test string.

There is an 'M' in the string.

That generally means you tried accessing something out of bounds.