下面程序的功能是在一个字符数组中查找一个指定的字符,若数组中含有该字符则输出该字符在数组中第一次出现的位置(下标值),否则输出-1。# include ____①____void main ( ){char ch = 'a' , str [50] ;int num , i , flag = 1 ;gets ( str ) ;num = ____②____;for ( i = 0 ; i < num ; i ++)if ( ____③____){flag = 0 ;break ;}if ( flag ==1 )printf ( "%d" , -1 ) ;else____④____;}