C Lecture 1

hello.c

#include <stdio.h>

int
main()
{
        /* A very simple program... */
        printf("Hello, world\n");
        return 0;
}

count.c


#include <stdio.h>
#include <string.h>

int
main()
{
    char buf[1024];
    int char_count = 0;
    int line_count;

    line_count = 0;
    while (fgets(buf, sizeof(buf), stdin)) {
        char_count += strlen(buf);
        line_count++;
    }
    printf(
     "File has %d characters in %d lines\n",
        char_count, line_count);
    return 0;
}

Data types

Integer data types:

	char c;
	int i, j;
	short int s;
	long int l;

Real numbers:

	double d;
	float f;

Pointers:

	int *p;

Arrays:

	char buf[1024];
	int nums[10];

Structures (records):

	struct tm {
	    int tm_sec;
	    int tm_min;
	    int tm_hour;
	    ...
	};

Unions (`variant' records):

	union name {
	    int i;
	    char str[12];
	};

Enumerations (groups of integer constants):

	enum Suits {
	    SPADE, HEART, CLUB, DIAMOND
	};

Strings in C

strings are characters stored sequentially in memory
the end is marked by a 0 (null) byte
arrays of characters often used to `create' memory for strings
only starting location is passed around
(e.g., to functions)

printf()

int printf(char *fmt, ...);

first argument is the format string
... means any number & type of other arguments
returns number of characters output
(EOF (-1) on error)
% in format string (fmt) introduces formatted argument:
- %d: replaced with integer argument
- %c: replaced with character argument
- %s: replaced with string argument
- %f: replaced with floating point argument
- %%: print a %.

Examples:

    int i = 10;
    double pi = 3.1415926535897932385;
    char letter = 'A';
    char *mesg = "hi";
    char buf[10] = "there";

    printf("i is %d, pi is %f\n",
	    i, pi);
    printf("more exact pi: %.20f\n", pi);
    printf("letter=%c mesg: %s, buf: %s\n",
	    letter, mesg, buf);

While statement

while (expr)
    statement

Examples:

    while (fgets(buf, sizeof(buf), stdin))
        lines++;



    int i;

    i = 0;
    while (i < 10) {
	printf("%d\n", i);
	i++;
    }

Do statement

do
    statement
while (expr);

Example:

    do {
        printf("Feed me: ");
        fflush(stdout);
    } while (fgets(buf, sizeof(buf),
                   stdin));

If statement

if (expr)
    statement
else
    statement

Example:

    if (grade < 0 || grade > 100) {
        printf(
      "Error: grade not in range 0..100\n"
         );
        return -1;
    }

    passed = 1;
    if (grade >= 80)
        letter = 'A';
    else if (grade >= 65)
        letter = 'B';
    else if (grade >= 55)
        letter = 'C';
    else if (grade >= 50)
        letter = 'D';
    else {
        letter = 'F';
        passed = 0;
    }

For statement

for (expr; expr; expr)
    statement

Examples:

    for (i = 0; i < 10; i++)
            printf("%d\n", i);

    factorial = 1;
    for (i = 0; i < 10; i++) {
	if (i)
	    factorial *= i;
        printf("factorial of %d is %d\n",
            i, factorial);
    }

Switch statement

switch (expr) {
  case const-expr:
    statements
  case const-expr:
    statements
    ...
  default:
    statements
}

Example:

    int optc;
    int verbose = 0;
    .
    .
    switch (optc) {
    case 'v':
        verbose = 1;
        break;
    case 'h':
    case 'H':
        print_help();
        exit(0);
    default:
        printf("Unknown option `%c'\n",
                optc);
        exit(1);
    }

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