Chapter 22.1, 2.2, 2.3 Answers

Answers to the odd-numbered questions are in the back of the text book.

2.1-2 The standard identifiers have particular meanings in C programs. Redefining standard identifiers for use as variables may mean that C can’t use them for their original purpose. Your program may not work as intended. The C compiler will not let you use reserved words as identifiers; that’s why the words are called “reserved”.

2.1-4 Using the word “PI” is clearer and less subject to typing error than using the string of digits. Defining it once, you can change the definition in that one place to add or remove precision and the change will be used everywhere that “PI” appears; you don’t have to make the change in more than one place. This makes your program easier to modify and maintain. PI is a constant that doesn’t change during the execution of the program, so it doesn’t need to be a variable.

2.2-2 int: 15, -999; double: 25.123, 15.0, 32e-4, .123; char: ‘x’, ‘*’The others are not valid C language int, double, or char constants.

2.2-P1 #define PI 3.14159

int num_circ;

double radius, area, circumf;

char circ_name;

2.3-2 Before: undefined. After execution: m=10, n=21.

2.3-4 Change the \n at the end of the sentence to be \n\n.

2.3-P1 printf(“Enter three integers: “);

scanf(“%d%d%d”, &first, &second, &third);

2.3-P2-a printf(“The value of x is %f\n”, x);

2.3-P2-b printf(“The area of a circle with radius %f is %f.\n”, radius, area);

2.3-P3 #include <.h>

#define PI 3.14159 /* sufficient accuracy for float math */

int main(void)

{

float radius; /* 6-7 decimal digits; 10E-38 to 10E38 */

printf(“Enter the radius of the circle: “);

scanf(“%f”, &radius);

printf(“The area of the circle with radius %f is %f.\n”,

radius, PI * radius * radius );

return(0); /* the operating system return code */

}