running the command in c
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char * strncat (char * dest, const char * src, size_t n) append (string), pointed to by src, at the end of the string pointed to by dest, with a length of up to n characters.
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strncpy char * (char * dest, const char * src, size_t n) copies up to n copies to n characters from the string pointed to by src to dest. in case the length of the src is smaller than n, the remainder or the remainder of dest will be filled with null values.
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the function size_t strcspn (const char * str1, const char * str2) calculates the length of the character segment of string str1 without containing the characters in str2.