在C中，为什么程序没有重新协调第二个if语句或大写char变量？

Question

Write a program that asks the user for an angle (in degrees). Then, ask the user to type a letter. If the user types a lower case letter, display the sine of the angle to four decimal places. If the user types an upper case letter, display the cosine of the angle to four decimal places.

So this is what i have so far, why will the program not recognize the upper case and print the cosine?

#include<stdio.h>
#include<math.h>

#define PI 3.14159265

main()
{
    int a;
    double x,y;
    char b;

    printf("What is the angle in degrees?\n");
    scanf("%i",&a);
    printf("Type a letter!\n");
    scanf("%i",&b);
    x=sin(a*PI/180);
    y=cos(a*PI/180);

    if (b>=97 | b<=122)
    {
        printf("The sine of %i is %.4f.\n",a,x);
    }
    if (b>=65 && b<=90) 
    {
        printf("The cosine of %i is %.4f.\n",a,y);
    }

    return 0;
}

Answer 1

Because if(b>= 97 | b <= 122) will always be true.

It should be if(b>=97 && b<=122) instead, which limits b in the range of lowercase.

Personally I prefer to write as if (97 <= b && b <= 122) which makes it easy to see its range.

Answer 2

Do you think this would be easier if you use the library <ctype.h> ?

#include <stdio.h>
#include <ctype.h>
#include <math.h>

#define PI 3.14159265

int main()

{
    int a;
    double x,y;
    char b;

    printf("What is the angle in degrees?\n");
    scanf("%d", &a);
    printf("Type a letter!\n");
    scanf(" %c", &b);

    x=sin(a*PI/180);
    y=cos(a*PI/180);

    if (isupper(b))
    {
        printf("The sine of %d is %.4f.\n",a,x);
    }
    else
    {
        printf("The cosine of %d is %.4f.\n",a,y);
    }

    return 0;
}