c - Recursive call that confuses me -

i have following function

int vowels(char *str) {     int count = 0;     if (! str[0])         return count;     if (strchr("aeiouaeiou", str[0]))         count ++;     return count + vowels(&str[1]); } 

that performs counting vowels appear in string, confuses me recursive call vowels(&str[1]) not understand why on every call goes next character, without doing str++. can me understand this? please.

within each function call declared like

int vowels(char *str); 

though declare like

size_t vowels( const char *str ); 

expression

&str[1] 

is equivalent to

str + 1 

or

++str 

however may not use

str++ 

because value of expression address stored in str before increment.

as me define function following way

size_t vowels( const char *s ) {     return *s ? ( strchr( "aeiouaeiou", *s ) != null ) + vowels( s + 1 ) : 0; }