/* File: hello_world.c                                      
 *                                                             
 * A simple program that prints "Hello World".                
 * main() is declared with no arguments, but no type checking  
*/

#include <stdio.h>

int main()
{
    printf("Hello World\n");
    return 0;
}

-----------------------------------------------------------------------------


/* File: hello_world2.c                            
 *                                                 
 * A simple program that prints "Hello World".     
 * main() is declared with its full arguments      
 */

#include <stdio.h>

int main(int argc, char *argv[])
{
    printf("Hello World\n");
    return 0;
}

-----------------------------------------------------------------------------


/* File: hello_world3.c                                        
 *                                                             
 * A simple program that prints "Hello World".                 
 * main() is declared with no arguments, allowing type checking 
 */

#include <stdio.h>

int main(void)
{
    printf("Hello World\n");
    return 0;
}

-----------------------------------------------------------------------------


/* File: sums.c
 *
 * A simple program that prints the sum of each number
 * from 0 to MAX_VALUE.
 */

#include <stdio.h>

#define MAX_VALUE       10                      /* The max sum to compute */

int main(void)
{
    int i;                                      /* generic loop variable  */
    int sum = 0;                                /* the sum accumulator    */

    for (i = 0; i <= MAX_VALUE; i++)
    {
        sum += i;                               /* short for sum = sum + i */
        printf("sigma %d = %d\n", i, sum);
    }

    return 0;
}

-----------------------------------------------------------------------------

/* File: capitalize.c
 *
 * Prints out a string in which all letters are capitalized
 */

#include <stdio.h>

#define STRING_LENGTH      80                      /* max length of string */

int main(void)
{
    char text[STRING_LENGTH] = "hello there";      /* the string */
    int i;                                         /* a loop counter */

    i = 0;
    while (text[i] != '\0')                        /* traverse the string */
    {
        if ((text[i] >= 'a') && (text[i] <= 'z'))  /* if a lowercase letter */
            text[i] = text[i] - 'a' + 'A';         /* then capitalize it    */
        i++;
    }

    printf("%s\n", text);

    return 0;
}


-----------------------------------------------------------------------------


/* File: concat.c
 *
 * Reads in strings and concats them into one long string.
 * Terminates and prints result when user enters "end".
 */
#include <stdio.h>                        /* Standard I/O library */
#include <string.h>                       /* The strings library  */

#define true                    1         /* define true and false */
#define false                   0
#define MAX_STRING              80        /* the max string length */
#define NO_MORE_INPUT           "end"     /* the terminating string */

int main(void)
{
    char instring[MAX_STRING];            /* the input string */
    char text[MAX_STRING];                /* the concatenated string */
    char done = false;                    /* flag when finished */

    text[0] = '\0';                       /* initialize the result string */

    while (!done)
    {
        if (scanf("%s", instring) != 1)   /*  read in string */
        {                                 /*  ... if there is an error ... */
            printf("Error reading input\n");
            done = true;
        }
        else if (!strcmp(instring, NO_MORE_INPUT))
        {                                 /* user types "end" */
            printf("%s\n", text);         /* print the final string */
            done = true;                  /* and exit */
        }
        else if (strlen(instring) + strlen(text) < MAX_STRING)
            strcat(text, instring);       /* still room, so concatenate */
        else                              /* otherwise we are out of space */
        {
            printf("Error: out of space\n");
            done = true;
        }
    }

    return 0;
}

-----------------------------------------------------------------------------

/* File: xchoosey.c
 *
 * An inefficient calculation of "x choose y"
 */

#include <stdio.h>

int factorial(int x);                   /* prototype for factorial function */

int main(void)
{
    int x = 10;
    int y = 3;
    int z;

    z = factorial(x) / (factorial(y) * factorial(x-y));
    printf("%d choose %d = %d\n", x, y, z);
    return 0;
}

/*
 * factorial() - takes an integer x and returns x!
 */
int factorial(int x)
{
    int accumulator = 1;

    while (x > 0)
    {
        accumulator = accumulator * x;
        x--;
    }

    return (accumulator);
}