编译错误“ s未声明”，但这是`scanf`的结果

Question

this is my code it is for calculating resistors in series or parallel the error is on line 12

if ( sp == s )

full code in case of earlier mistake

#include <stdio.h>

int main ( void ) {
    char sp ;
    float a, b, resistancep, resistances ;
    printf ("Enter s for resistor in series or p for parallel\n") ;
    scanf ( " %c", &sp ) ;
    printf ("Enter two resistors calculate\n" ) ;
    scanf ("%f%f", &a, &b ) ;
    resistancep = a * b / ( a + b ) ;
    resistances = a + b ;
    if ( sp == s ) {
            printf ( "The total resistance is%f\n", resistances ) ;
    }
else {
            printf ( "The total resistance is%f\n", resistancep ) ;
    }

I have also tried

if ( sp == "s" )

and

if ( sp, s )

Answer 1

You probably want

if ( sp == 's' )

Just s is looking for a variable named s, which you haven't declared.

"s" usually refers to a string , which is an array of characters. You are reading a single character off of input, and "s" != 's' . Remember, and array (almost) never equals an element of the array.