Difference between revisions of "Principles of Computer Programming"
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− | 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 | + | 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 to wait until the user presses a key to exit. You can use the following code to do this. |
#include <conio.h> | #include <conio.h> |
Revision as of 12:20, 14 January 2020
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 to wait until the user presses 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); }