Principles of Computer Programming
From David Vernon's Wiki
Here are some code segments for the examples in the course on principles of computer programming.
/* Example 1 */
/* This is a C program to ask you to type a letter */
/* and then to tell you what you typed */
#include <stdio.h>
void main() {
char letter;
printf("Please type a letter & then press Return >>");
scanf("%c",&letter);
printf("You typed the letter %c", letter);
}
If you compile and run this on Microsoft Visual C++, you won't see anything because the window in which the program executes disappears as soon as the program exits. One solution is wait until the user to press a key to exit. You can use the following code to do this.
#include <conio.h>
...
printf("\nPress any key to continue\n");
_getch();
Here are the rest of the examples.
/* Example 2 */
/* This is a C program to ask you to enter two */
/* numbers; it then compares them and prints a */
/* message to say whether they are equal or not */
#include <stdio.h>
void main() {
int first_number, second_number;
printf("Type a number and then press Enter >>");
scanf("%d",&first_number);
printf("Type another number and then press Enter >>");
scanf("%d",&second_number);
if (first_number == second_number)
printf("The two numbers %d are identical", first_number);
else
printf("The two numbers %d and %d are different", first_number, second_number);
}
/* Example 2b */
/* This is a C program to ask you to enter three */
/* numbers; it then compares them and prints a */
/* message to say whether they are equal or not */
#include <stdio.h>
void main() {
int first_number, second_number, third_number;
printf("Please type three numbers .... \n");
printf("Enter the first number >>");
scanf("%d",&first_number);
printf("Enter the second number >>");
scanf("%d",&second_number);
printf("Enter the third number >>");
scanf("%d",&third_number);
if (first_number == second_number)
if (second_number == third_number)
printf("The three numbers %d are identical",
first_number);
if (first_number != second_number)
if (second_number != third_number)
if (first_number != third_number)
printf("The three numbers %d %d %d are all different",
first_number, second_number, third_number);
}
/* Example 3a */
/* Compute the total value of 7 Scrabble letters */
/* Input: the user is prompted to enter each letter */
/* in turn */
/* Output: the program prints the sum of the seven */
/* individual letter values */
#include <stdio.h>
#include <ctype.h>
#define TRUE 1
#define FALSE 0
void main() {
char letter, enter;
int scrabble_value,
total_scrabble_value,
i; /* not the same as 'i' */
int debug;
/* debug is a flag. If it is TRUE we will execute some printf */
/* statements to help see what the program is doing. */
/* if it is FALSE, we won't! */
debug = TRUE;
/* initialize variables */
total_scrabble_value = 0;
scrabble_value = 0;
/* use a for loop to read seven values*/
for (i=0; i < 7; i++)
{
printf("Please type a letter and then press Return >>");
scanf("%c",&letter);
scanf("%c",&enter); /* skip enter character */
letter = toupper(letter); /* convert the letter to uppercase */
/* note this works even if the letter */
/* is already in upper case */
if ((letter == 'A') ||
(letter == 'E') ||
(letter == 'I') ||
(letter == 'L') ||
(letter == 'N') ||
(letter == 'O') ||
(letter == 'R') ||
(letter == 'S') ||
(letter == 'T') ||
(letter == 'U'))
{
scrabble_value = 1;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
else
if ((letter == 'D') ||
(letter == 'G'))
{
scrabble_value = 2;
if (debug == TRUE) {
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
}
else
if ((letter == 'B') ||
(letter == 'C') ||
(letter == 'M') ||
(letter == 'P'))
{
scrabble_value = 3;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
else
if ((letter == 'F') ||
(letter == 'H') ||
(letter == 'V') ||
(letter == 'W') ||
(letter == 'Y'))
{
scrabble_value = 4;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
else
if ((letter == 'K'))
{
scrabble_value = 5;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
else
if ((letter == 'J') ||
(letter == 'X') )
{
scrabble_value = 8;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
else
if ((letter == 'Z') ||
(letter == 'Q') )
{
scrabble_value = 10;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
else
printf("You typed the character %c ... that's not allowed\n", letter);
/* now add the value to the total */
total_scrabble_value = total_scrabble_value + scrabble_value;
}
printf("The Scrabble value of the seven letters is %d",
total_scrabble_value);
}
/* Example 3b */
/* Compute the total value of 7 Scrabble letters */
/* Input: the user is prompted to enter each letter */
/* in turn */
/* Output: the program prints the sum of the seven */
/* individual letter values */
#include <stdio.h>
#include <ctype.h>
#define TRUE 1
#define FALSE 0
void main() {
char letter, enter;
int scrabble_value,
total_scrabble_value,
i; /* not the same as 'i' */
int debug;
/* debug is a flag. If it is TRUE we will execute some printf */
/* statements to help see what the program is doing. */
/* if it is FALSE, we won't! */
debug = TRUE;
/* initialize variables */
total_scrabble_value = 0;
scrabble_value = 0;
/* use a for loop to read seven values*/
for (i=0; i < 7; i++)
{
printf("Please type a letter and then press Return >>");
scanf("%c",&letter);
scanf("%c",&enter); /* skip enter character */
letter = toupper(letter); /* convert the letter to uppercase */
/* note this works even if the letter */
/* is already in upper case */
switch (letter) {
case 'A':
case 'E':
case 'I':
case 'L':
case 'N':
case 'O':
case 'R':
case 'S':
case 'T':
case 'U': scrabble_value = 1;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
break;
case 'D':
case 'G': scrabble_value = 2;
if (debug == TRUE) {
printf("the letter %c has the value %d\n", letter, scrabble_value);
}
break;
case 'B':
case 'C':
case 'M':
case 'P': scrabble_value = 3;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
break;
case 'F':
case 'H':
case 'V':
case 'W':
case 'Y': scrabble_value = 4;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
break;
case 'K': scrabble_value = 5;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
break;
case 'J':
case 'X': scrabble_value = 8;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
break;
case 'Z':
case 'Q': scrabble_value = 10;
if (debug == TRUE)
printf("the letter %c has the value %d\n", letter, scrabble_value);
break;
default: printf("You typed the character %c ... that's not allowed\n", letter);
break;
} /* end of the switch statement */
/* now add the value to the total */
total_scrabble_value = total_scrabble_value + scrabble_value;
}
printf("The Scrabble value of the seven letters is %d",
total_scrabble_value);
}
/* A program to prompt the user three times and reads three numbers. */
/* It compare these three numbers and tell the user whether */
/* */
/* - all three numbers are the same */
/* - all three numbers are different */
/* - just two numbers are the same */
/* in this case, it also tells the user which two numbers they are */
/* */
/* The program continues to ask the user for input until he enters */
/* three zeros. */
#include <stdio.h>
#define TRUE 1
#define FALSE 0
void main() {
int n1, n2, n3;
/* give the numbers initial values */
n1 = 1;
n2 = 1;
n3 = 1;
/* while the three numbers are not all zero */
while ((n1 != 0) && (n2 != 0) && (n3 != 0)) {
printf("Please enter the first number >>");
scanf("%d",&n1);
printf("Please enter the second number >>");
scanf("%d",&n2);
printf("Please enter the third number >>");
scanf("%d",&n3);
/* check to see if they are all the same */
if ((n1 == n2) && (n2 == n3) && (n1 == n3)) {
printf(" The three numbers are all the same. \n");
}
else {
if ((n1 != n2) && (n2 != n3) && (n1 != n3)) {
printf("The three numbers are all the different.\n");
}
else {
/* two are the same - which are they? */
if (n1 == n2) {
printf("The first and second numbers are the same: %d\n”,
n1, n2);
}
else {
if (n2 == n3) {
printf("The second and third numbers are the same: %d\n",
n2, n3);
}
else { /* no need to check if the first and third */
/* are the same ... it's the only possibility */
printf("The first and third numbers are the same:%d\n",
n1, n2);
}
}
}
}
}
}
/* a program to call a function called max */
/* max returns the maximum of two floating point numbers */
#include <stdio.h>
float max(float a, float b)
{
float c; /* local variable */
if (a > b) {
c = a;
}
else {
c = b;
}
return(c);
}
void main()
{
FILE *fp_in, *fp_out;
float x, y, z;
int end_of_file;
/* open the files */
/* no checking for the moment */
fp_in = fopen("input.txt", "r");
fp_out = fopen("max.txt", "w");
end_of_file = fscanf(fp_in, "%f %f", &x, &y);
while (end_of_file != EOF)
{
z = max(x, y);
fprintf(fp_out, "%5.2f\n ", z);
end_of_file = fscanf(fp_in, "%f %f", &x, &y);
};
fclose(fp_in);
fclose(fp_out);
}
/* Program to read pairs of numbers from the input file */
/* and calls a function max which returns the maximum of */
/* of two floating point numbers. */
/* This maximum is then written to an output file */
/* the input file is read until we reach the end of file */
#include <stdio.h>
float max(float a, float b)
{
float c; /* local variable */
if (a > b) {
c = a;
}
else {
c = b;
}
return(c);
}
void main()
{
FILE *fp_in, *fp_out;
float x, y, z;
int end_of_file;
/* open the files */
/* no checking for the moment */
fp_in = fopen("input.txt", "r");
fp_out = fopen("max.txt", "w");
/* read until we reach the end of file ... version A */
end_of_file = fscanf(fp_in, "%f %f", &x, &y);
while (end_of_file != EOF)
{
z = max(x, y);
fprintf(fp_out, "%5.2f\n ", z);
end_of_file = fscanf(fp_in, "%f %f", &x, &y);
};
/* read until we reach the end of file ... version B */
/* note: this version is equivalent to version A */
/* but it puts the fscanf in the while condition */
/* while (fscanf(fp_in, "%f %f", &x, &y) != EOF) */
/* { */
/* z = max(x, y); */
/* fprintf(fp_out, "%5.2f\n ", z); */
/* }; */
fclose(fp_in);
fclose(fp_out);
}
/* Program to read a sequence of numbers from the input file, */
/* compute the average of the numbers (ignoring zeros) */
/* replace all occurrences of zero with the average */
/* and write the numbers to an output file */
/* Note: we use four loops ... we could use fewer but it */
/* means doing more than one thing in each loop ... */
/* we will do this next day. */
#include <stdio.h>
#define MAX 100
void main()
{
FILE *fp_in, *fp_out;
float numbers[MAX];
float average, sum=0;
int n, count, i, non_zeros;
int end_of_file;
/* open the files */
/* no checking for the moment */
fp_in = fopen("input.txt", "r");
fp_out = fopen("output.txt", "w");
/* read until we reach the end of file ... version A */
/* store all the numbers in an array */
count= 0;
end_of_file = fscanf(fp_in, "%d", &n);
while (end_of_file != EOF)
{
numbers[count] = n;
count = count + 1;
end_of_file = fscanf(fp_in, "%d", &n);
}
/* the integers are in the array numbers and the variable count */
/* hold the number we read */
/* find the average but ignore the zeros */
sum = 0;
non_zeros = 0;
for (i=0; i<count; i++)
{
if (numbers[i] != 0) {
sum = sum + numbers[i];
non_zeros = non_zeros + 1;
}
}
average = sum / non_zeros;
/* replace the zero with the average */
for (i=0; i<count; i++)
{
if (numbers[i] == 0) {
numbers[i]= average;
}
}
/* write out all the numbers to the output file */
for (i=0; i<count; i++)
{
fprintf(fp_out, "%f ", numbers[i]);
}
fclose(fp_in);
fclose(fp_out);
}
/* Program to read a file of integer numbers, 5 per line */
/* the 5 numbers represent the x, y, r, g, b values of a point */
/* Each point is stored in an array */
/* Write out the r, g, b values of each point to an output file */
/* */
/* Input file: points.txt */
/* Output file: colours.txt */
/* */
/* NOTE: this program is intended to illustrate the use of */
/* structures in C */
#include <stdio.h>
main() {
/*** define structure types ***/
struct colour {
int red;
int green;
int blue;
};
struct point {
int x;
int y;
struct colour clr;
};
FILE *fin, *fout;
struct point ps[100]; /* assume a maximum of 100 points in the input file */
int temp_r, temp_g, temp_b, temp_x, temp_y, i, count;
fin = fopen("points.txt", "r");
if (fin == 0) {
printf("Error ... can't open file points.txt\n");
exit(0);
}
fout = fopen("colours.txt", "w");
if (fout == 0) {
printf("Error ... can't open file colours.txt\n");
exit(0);
}
/* files are open so now we read in the point information */
i = 0;
while (fscanf(fin, "%d %d %d %d %d", &temp_x, &temp_y,
&temp_r, &temp_g, &temp_b) != EOF) {
/* store the values read in my array of points */
ps[i].x = temp_x;
ps[i].y = temp_y;
ps[i].clr.red = temp_r;
ps[i].clr.green = temp_g;
ps[i].clr.blue = temp_b;
i++;
}
/* remember how many points we read */
count = i;
/* now write out just the rgb values to the output file */
for (i=0; i<count; i++) {
fprintf(fout, "%d %d %d \n", ps[i].clr.red, ps[i].clr.green, ps[i].clr.blue);
}
fclose(fin);
fclose(fout);
}
/* Program to read a file of integer numbers, 5 per line */
/* the 5 numbers represent the x, y, r, g, b values of a point */
/* Each point is stored in an array */
/* Remove all duplicate points (i.e. points with the same x y */
/* value. */
/* Write out the x, y, r, g, b values of each point to an */
/* file */
/* */
/* Input file: points.txt */
/* Output file: new_points.txt */
/* */
/* NOTE: this program is intended to illustrate the use of */
/* structures in C */
#include <stdio.h>
main() {
/*** define structure types ***/
struct colour {
int red;
int green;
int blue;
};
struct point {
int x;
int y;
struct colour clr;
};
FILE *fin, *fout;
struct point ps[100]; /* assume a maximum of 100 points in the input file */
int temp_r, temp_g, temp_b, temp_x, temp_y, i, j, k, count;
fin = fopen("points.txt", "r");
if (fin == 0) {
printf("Error ... can't open file points.txt\n");
exit(0);
}
fout = fopen("new_points.txt", "w");
if (fout == 0) {
printf("Error ... can't open file colours.txt\n");
exit(0);
}
/* files are open so now we read in the point information */
i = 0;
while (fscanf(fin, "%d %d %d %d %d", &temp_x, &temp_y,
&temp_r, &temp_g, &temp_b) != EOF) {
/* store the values read in my array of points */
ps[i].x = temp_x;
ps[i].y = temp_y;
ps[i].clr.red = temp_r;
ps[i].clr.green = temp_g;
ps[i].clr.blue = temp_b;
i++;
}
/* remember how many points we read */
count = i;
/*** this section eliminates the duplicate values ***/
/* look at each element in turn */
for (i=0; i<count; i++) {
/* check for duplicates in all the remaining elements */
for (j=i+1; j<count; j++) {
if ((ps[j].x == ps[i].x) && (ps[j].y == ps[i].y)) {
/* we have found duplicate so shift all the rest */
for (k=j; k<count-1; k++) {
ps[k] = ps[k+1];
}
count = count - 1;
j--; /* decrement j so that when it is incremented in the */
/* for loop it will still index the same element, */
/* i.e. the element that was shifted into the j position */
}
}
}
/* now write out the x, y, r, g, b values to the output file */
for (i=0; i<count; i++) {
fprintf(fout, "%5d %5d %5d %5d %5d \n",
ps[i].x, ps[i].y, ps[i].clr.red, ps[i].clr.green, ps[i].clr.blue);
}
fclose(fin);
fclose(fout);
}
