#include <errno.h> 
#include <math.h> 
#include <stdio.h> 
 
main() 
{ 
   double input, square_root; 
 
   printf("Enter a number: "); 
   scanf("%le", &input); 
   errno = 0; 
   square_root = sqrt(input); 
 
   if (errno == EDOM) 
      perror("Input was negative"); 
   else 
      printf("Square root of %e = %e\n", 
              input, square_root); 
} 

$ CREATE IEEE_INFINITY.C 
#include <fp.h> 
 
double my_huge_val = HUGE_VAL 
^Z 
$ CC /FLOAT=IEEE/IEEE=DENORM IEEE_INFINITY 
 
double my_huge_val = HUGE_VAL; 
.....................^ 
%CC-E-NEEDCONSTEXPR, In the initializer for my_huge_val, "decc$gt_dbl_infinity" 
is not constant, but occurs in a context that requires a constant expression. 
at line number 3 in file WORK1$:[RTL]IEEE_INFINITY.C;1 
$ 

/*        CHAP_7_MATH_EXAMPLE.C                                 */ 
 
/* This example uses two functions --- mytan and main ---       */ 
/* to calculate the tangent value of a number, and to check     */ 
/* the calculation using the sin and cos functions.             */ 
 
#include <math.h> 
#include <stdio.h> 
 
/* This function calculates the tangent using the sin and       */ 
/* cos functions.                                               */ 
 
double mytan(x) 
    double x; 
{ 
    double y, 
           y1, 
           y2; 
 
    y1 = sin(x); 
    y2 = cos(x); 
 
    if (y2 == 0) 
        y = 0; 
    else 
        y = y1 / y2; 
 
    return y; 
} 
main() 
{ 
    double x; 
 
    /*  Print values: compare   */ 
    for (x = 0.0; x < 1.5; x += 0.1) 
        printf("tan of %4.1f = %6.2f\t%6.2f\n", x, mytan(x), tan(x)); 
} 

$ RUN  EXAMPLE
tan of  0.0 =   0.00      0.00
tan of  0.1 =   0.10      0.10
tan of  0.2 =   0.20      0.20
tan of  0.3 =   0.31      0.31
tan of  0.4 =   0.42      0.42
tan of  0.5 =   0.55      0.55
tan of  0.6 =   0.68      0.68
tan of  0.7 =   0.84      0.84
tan of  0.8 =   1.03      1.03
tan of  0.9 =   1.26      1.26
tan of  1.0 =   1.56      1.56
tan of  1.1 =   1.96      1.96
tan of  1.2 =   2.57      2.57
tan of  1.3 =   3.60      3.60
tan of  1.4 =   5.80      5.80
$ 

/*        CHAP_8_MEM_MANAGEMENT.C                               */ 
 
/* This example takes lines of input from the terminal until    */ 
/* it encounters a Ctrl/Z, places the strings into an           */ 
/* allocated buffer, copies the strings to memory allocated for */ 
/* structures, prints the lines back to the screen, and then    */ 
/* deallocates all the memory used for the structures.          */ 
 
#include  <stdlib.h> 
#include  <stdio.h> 
#define   MAX_LINE_LENGTH  80 
 
struct line_rec {               /*  Declare the structure.   */ 
    struct line_rec *next;      /*  Pointer to next line.    */ 
    char *data;                 /*  A line from terminal.    */ 
}; 
 
int main(void) 
{ 
    char *buffer; 
 
    /* Define pointers to        */ 
    /*  structure (input lines). */ 
 
    struct line_rec *first_line = NULL, 
            *next_line, 
            *last_line = NULL; 
 
    /* Buffer points to memory.  */ 
    buffer = malloc(MAX_LINE_LENGTH); 
 
    if (buffer == NULL) {       /* If error ...  */ 
        perror("malloc"); 
        exit(EXIT_FAILURE); 
    } 
 
    while (gets(buffer) != NULL) {      /* While not Ctrl/Z ...  */ 
        /* Allocate for input line.  */ 
        next_line = calloc(1, sizeof (struct line_rec)); 
 
        if (next_line == NULL) { 
            perror("calloc"); 
            exit(EXIT_FAILURE); 
        } 
 
        /* Put line in data area.    */ 
        next_line->data = buffer; 
 
        if (last_line == NULL)  /* Reset pointers.   */ 
            first_line = next_line; 
        else 
            last_line->next = next_line; 
 
        last_line = next_line; 
        /* Allocate space for the     */ 
        /*  next input line.          */ 
        buffer = malloc(MAX_LINE_LENGTH); 
 
        if (buffer == NULL) { 
            perror("malloc"); 
            exit(EXIT_FAILURE); 
        } 
    } 
    free(buffer);       /* Last buffer always unused. */ 
    next_line = first_line;     /* Pointer to beginning.  */ 
 
    while (next_line != NULL) { 
        puts(next_line->data);  /* Write line to screen.  */ 
        free(next_line->data);  /* Deallocate a line.     */ 
        last_line = next_line; 
        next_line = next_line->next; 
        free(last_line); 
    } 
 
    exit(EXIT_SUCCESS); 
} 

$ RUN  EXAMPLE
line one
line two
[Ctrl/Z]
EXIT
line one
line two
$ 

/*        CHAP_9_GET_USER.C                                   */ 
 
/* Using cuserid, this program returns the user name.         */ 
 
#include <stdio.h> 
 
main() 
{ 
    static char string[L_cuserid]; 
 
    cuserid(string); 
    printf("Initiating user: %s\n", string); 
} 

$ RUN  EXAMPLE1
Initiating user: TOLLIVER

/*        CHAP_9_GETTERM.C                              */ 
 
/* Using getenv, this program returns the terminal.     */ 
 
#include <stdio.h> 
#include <stdlib.h> 
 
main() 
{ 
    printf("Terminal type: %s\n", getenv("TERM")); 
} 

$ RUN  EXAMPLE3
Terminal type: vt100-132

/*       CHAP_9_CHANGE_DIR.C                                    */ 
    
/* This program performs the equivalent of the DCL command      */ 
/* SET DEFAULT SYS$LOGIN. However, once the program exits, the  */ 
/* directory is reset to the directory from which the program   */ 
/* was run.                                                     */ 
 
#include <stdio.h> 
#include <unistd.h> 
#include <stdlib.h> 
 
main() 
{ 
    char *dir; 
    int i; 
 
    dir = getenv("HOME"); 
    if ((i = chdir(dir)) != 0) { 
        perror("Cannot set directory"); 
        exit(0); 
    } 
 
    printf("Current directory: %s\n", dir); 
} 

$ RUN EXAMPLE4
Current directory: dba0:[tolliver]
$ 

/*        CHAP_9_DATE_TIME.C                                    */ 
 
/* The time function returns the time in seconds; the localtime */ 
/* function converts the time to hours, minutes, and so on;     */ 
/* the strftime function uses these values to obtain a string   */ 
/* in the desired format.                                       */ 
 
#include <time.h> 
#include <stdio.h> 
 
#define MAX_STRING 80 
 
main() 
{ 
    struct tm *time_structure; 
    time_t time_val; 
    char output_str[MAX_STRING]; 
 
    time(&time_val); 
    time_structure = localtime(&time_val); 
 
    /* Print the date  */ 
 
    strftime(output_str, MAX_STRING, 
             "Today is %A, %B %d, %Y", time_structure); 
 
    printf("%s\n", output_str); 
 
    /* Print the time using a 12-hour clock format. */ 
 
    strftime(output_str, MAX_STRING, 
             "The time is %I:%M %p", time_structure); 
 
    printf("%s\n", output_str); 
}    

$ RUN  EXAMPLE5
Today is Thursday, May 20, 1993
The time is 10:18 AM
$