C: Some examples
By Abhishek
Some C code that I wrote when I was learning C
Example 1:
/* vis: make funny characters visible */
#include <stdio.h>
#include <ctype.h>
main(argc, argv)
int argc;
char *argv[]; /* argv[0] is the command name itself so the
first argument is argv[1] */
{
int c;
int strip = 0;
if (argc > 1 && strcmp(argv[1],"-s") == 0 )
strip = 1;
while ((c = getchar()) != EOF)
if (isascii(c) && (isprint(c) || c=='\n' || c=='\t' || c==' '))
putchar(c);
else if (strip == 0)
printf("\\%03o", c);
putchar('\n');
exit(0);
}
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Example 2:
/*
visf: make funny characyers visible
Use -s to strip of printing characters
The input must be a file(s)
*/
#include <stdio.h>
#include <ctype.h>
int strip = 0; /* discard special characters when = 1 */
main(argc, argv)
int argc;
char *argv[];
{
int i;
FILE *fp; /* Declare a pointer to a file */
while (argc > 1 && argv[1][0] == '-')
{
switch (argv[1][1])
{
case 's':
strip = 1;
break;
default:
fprintf(stderr, "%s: unknown arg %s\n",
argv[0], argv[1]);
exit(1);
}
argc--;
argv++;
}
if (argc == 1)
vis(stdin);
else
for (i = 1; i < argc; i++)
if ((fp=fopen(argv[i], "r")) == NULL)
{
fprintf(stderr, "%s: cannot open %s\n",
argv[0], argv[i]);
exit(1);
}
else
{
vis(fp);
fclose(fp);
}
exit(0);
}
vis(fp)
FILE *fp;
{
int c;
while (( c = getc(fp)) != EOF)
if (isascii(c) && (isprint(c) || c=='\n' || c=='\t' ||
c==' '))
putchar(c);
else if (!strip)
printf("\\%03o", c);
putchar('\n');
}
DEMO 2:
$ a.out -x
a.out: unknown arg -x
$ a.out -s planet
-s: cannot open planet
$ cat planet.dat
Earth@øið@# A‰7KÇsaturnvenus@333333@$
$ a.out -s planet.dat
Earth@i@#A7Ksaturnvenus@333333@
$ a.out planet.dat
Earth\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\00
0@\370i\360\000\000\000\000@#\240A\2117K\307saturn\000\000\000\000\000\000\000\0
00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
00\000\000\000\000\000\000venus\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000@\013333333@\024\000\000\000\000\000\000
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Example 3:
/* p: print input in chunks */
#include <stdio.h>
#define PAGESIZE 22
char *progname; /* program name for error message */
main(argc, argv)
int argc;
char *argv[]; /* argv[0] is the command name itself so the
first argument is argv[1] */
{
int i;
FILE *fp, *efopen();
progname = argv[0];
if (argc == 1)
print(stdin, PAGESIZE);
else
for (i = 1; i < argc; i++)
{
fp = efopen(argv[i], "r");
print(fp, PAGESIZE);
fclose(fp);
}
exit(0);
}
/* function to open the file */
FILE *efopen(file, mode)
char *file, *mode;
{
FILE *fp, *fopen();
extern char *progname;
if ((fp = fopen(file, mode)) != NULL)
return fp;
fprintf(stderr, "%s: cannot open file %s mode %s \n",
progname, file, mode);
exit(1);
}
/* function to print fp in pagesize chuncks */
print(fp, pagesize)
FILE *fp;
int pagesize;
{
static int lines = 0; /* number of lines so far */
char buf[BUFSIZ];
while (fgets(buf, sizeof buf, fp) != NULL)
if ( ++lines < pagesize)
fputs(buf, stdout);
else
{
buf[strlen(buf) - 1] = '\0';
fputs(buf, stdout);
fflush(stdout);
ttyin();
lines = 0;
}
}
/* function to process response from terminal */
ttyin()
{
char buf[BUFSIZ];
FILE *efopen();
static FILE *tty = NULL; /* static to retain value */
if (tty == NULL) /* Open in first call only */
tty = efopen("/dev/tty", "r");
if (fgets(buf, BUFSIZ, tty) == NULL || buf[0] == 'q')
exit(0);
else
return buf[0]; /* ordinary line */
}
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Example 4:
#include <stdio.h>
main()
{
char name[26];
puts("What is your name: "); /* write string to stdout */
gets(name); /* Get string from stdin */
puts("Hello. How are you ?? ");
puts(name);
}
Demo 4:
$ a.out
What is your name:
Abhishek
Hello. How are you ??
Abhishek
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Example 5:
#include <stdio.h>
main()
{
char grade;
printf("Please enter the grade: ");
grade=getchar();
fflush(stdin);
switch (grade)
{
case 'A':
printf("The HRA percentage for grade %c is 45\n", grade);
break;
case 'B':
printf("The HRA percentage for grade %c is 40\n", grade);
break;
case 'C':
printf("The HRA percentage for grade %c is 30\n", grade);
break;
case 'D':
printf("The HRA percentage for grade %c is 25\n", grade);
break;
default:
printf("Invalid grade %c. try again.\n", grade);
exit(10);
}
}
Demo 5:
$ a.out
Please enter the grade: S
Invalid grade S. try again.
$ a.out
Please enter the grade: A
The HRA percentage for grade A is 45
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Example 6:
/* This program accepts characters from keyboard until character '!' is
input and compares the number of vowels and consonants entered */
#include <stdio.h>
main()
{
char input;
int num_vowel = 0;
int num_consonant = 0;
printf("Please insert characters. (Enter ! to quit)\n");
input = getchar();
while (input != '!')
{
switch (input)
{
case 'a':
case 'e':
case 'i':
case 'o':
case 'u':
num_vowel++;
break;
default:
num_consonant++;
break;
}
input = getchar();
}
printf("Number of vowels: %d\n", num_vowel);
printf("Number of consonants: %d\n", num_consonant);
}
Demo 6:
$ a.out
Please insert characters. (Enter ! to quit)
dsfgsdbafdfsion!
Number of vowels: 3
Number of consonants: 12
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Example 7:
/* Some examples of pointers */
#include "stdio.h";
main()
{
char *name = "abhishek"; /* Declare a pointer to a char */
char *address[3]; /* Declare an array of pointer to char */
printf("Value of *name: %c\n", *name);
printf("Value of name: %i\n", name);
printf("String pointed by name: %s\n", name);
printf("The third character in name: %c\n", *(name + 2));
printf("The third character in name: %c\n", name[2]);
address[0] = "Bhopal";
address[1] = "KC";
address[2] = "SLC";
printf("Value of address: %i\n", address);
printf("Value of address[0]: %i\n", address[0]);
printf("Contents of *address: %s\n", *address);
printf("Contents of *(address + 1): %s\n", *(address + 1));
printf("Contents of *(address + 1): %s\n", *(address + 1));
printf("Contents of *(address + 2): %s\n", *(address + 2));
printf("Contents of (*(address + 1) + 1): %s\n", (*(address + 1) + 1));
}
Demo 7:
$ a.out
Value of *name: a
Value of name: 1073746112
String pointed by name: abhishek
The third character in name: h
The third character in name: h
Value of address: 2063837192
Value of address[0]: 1073746288
Contents of *address: Bhopal
Contents of *(address + 1): KC
Contents of *(address + 2): SLC
Contents of (*(address + 1) + 1): C
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