But instead the code you will review written by a previous COMP1511 student.
Discuss the weakness of the style in the code below and how it might be improved:
// Test if a point is inside a triangle.
// Julian Saknussemm
//
// Given Three points of a triangle, and another arbitrary point this program determines if that point lies inside
// the triangle.
//
// This is determined by satisfying the following rule:
// A point P(x,y) is inside triangle A(x0,y0), B(x1,y1), C(x2,y2)
// iff
// P is on the same side of the line AB as C
// P is on the same side of the line BC as A
// and
// P is on the same side of the line AC as B
//
// A special case exits for a vertical line (inf gradient) when testing the side of the line
#include <stdio.h>
int test2( double px, double py, double m, double b )
{ if( py < m * px + b ) {
return -1; // point is under line
}else if ( py == m * px + b ){
return 0;
} else {
return 1; // over
}
}
int // two points lie on the same side of a line
test1( double px, double py, double m,double b, double lx,double ly) {
return (test2( px,py, m,b )==test2(lx,ly,m,b));
}
int tritest(double x0,double y0,double x1,double y1,double x2,double y2,double px, double py){
int line1, line2, line3;
// line eqns
double m01 = (y1-y0)/(x1-x0);
// b: y - y1 = m( x - x1 ), x = 0
double b01 = m01 * -x1 + y1;
double m02, m12, b02, b12;
m02 = (y2-y0)/(x2-x0);
m12 = (y2-y1)/(x2-x1);
b02 = m02 * -x2 + y2;
b12 = m12 * -x2 + y2;
// vertical line checks
if( x1 == x0 ) {
line1 = ( (px <= x0) == (x2 <= x0) );
} else {
line1 = test1( px, py, m01, b01,x2,y2);
}
if( x1 == x2 ) {
line2 = ( (px <= x2) == (x0 <= x2) );
} else {
line2 = test1(px,py, m12, b12,x0,y0);
}
if( x2 == x0 ) {
line3 = ( (px <= x0 ) == (x1 <= x0) );} else {
line3 = test1(px, py, m02,b02,x1,y1);
}
return line1 && line2 && line3;
}
int main(int argc, char* argv[]) {
double x0,y0,x1,y1,x2,y2,px;
double py;
int scanfsReturnValueAggregatedOverAllScanfs = 0;
// get input
printf("Triangle Vertex A (x,y): "); scanfsReturnValueAggregatedOverAllScanfs += scanf("%lf,%lf", &x0,&y0);
printf("Triangle Vertex B (x,y): "); scanfsReturnValueAggregatedOverAllScanfs += scanf("%lf,%lf", &x1,&y1);
printf("Triangle Vertex C (x,y): "); scanfsReturnValueAggregatedOverAllScanfs += scanf("%lf,%lf", &x2,&y2);
printf("Test Point (x,y): "); scanfsReturnValueAggregatedOverAllScanfs += scanf("%lf,%lf", &px,&py);
// print error
if( scanfsReturnValueAggregatedOverAllScanfs != 8 ) {
printf("You're stupid and didn't put in the right inputs!\n");
return 1;
}
// print answer
printf("Point (%.2lf,%.2lf) is ", px,py);
if(tritest(x0,y0,x1,y1,x2,y2,px,py)) printf("inside");
else printf("outside");
printf(" the Triangel\n");
// return 0
return 0;
}
sum_digits.c which reads characters from its input
and counts digits.
When the end of input is reached it should print a count of how many digits occurred in its input and their sum.
The only functions you can use are getchar and printf.
For example:
./sum_digits 1 2 3 o'clock 4 o'clock rock Input contained 4 digits which summed to 10 ./sum_digits 12 twelve 24 twenty four thirty six 36 Input contained 6 digits which summed to 18
Your tutor may still choose to cover some of the questions time permitting.
letter_triangle.c
that read an positive integer n and outputs a triangle of letters
of height n as below.
For example:
./letter_triangle
Enter height: 3
A
BCB
DEFED
./letter_triangle
Enter height: 7
A
BCB
DEFED
GHIJIHG
KLMNONMLK
PQRSTUTSRQP
VWXYZABAZYXWV
./letter_triangle
Enter height: 10
A
BCB
DEFED
GHIJIHG
KLMNONMLK
PQRSTUTSRQP
VWXYZABAZYXWV
CDEFGHIJIHGFEDC
KLMNOPQRSRQPONMLK
TUVWXYZABCBAZYXWVUT
input_statistics.c that for the characters provided on standard input:
For example:
./input_statistics
"Beauty is truth, truth beauty," -- that is all
Ye know on earth, and all ye need to know.
Input contains 27 blanks, tabs and new lines
Number of words: 19
Length of shortest word: 2
Length of longest word: 8
./input_statistics
And here is another example with only one line of input!!!!!!!!!
Input contains 11 blanks, tabs and new lines
Number of words: 11
Length of shortest word: 2
Length of longest word: 14
matrix below hold?
#include <stdio.h>
#define N_ROWS 12
#define N_COLUMNS 15
int main(void) {
int matrix[N_ROWS][N_COLUMNS];
Write nested loops that set every element of matrix.
Each element should be set to the product of its two indices.
Write nested loops that print the elements of matrix plus sums of each
row and sums of each column.
The output of your code should look like this:
a.out
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 | 0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 | 105
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 | 210
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 | 315
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 | 420
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 | 525
0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 | 630
0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 | 735
0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 | 840
0 9 18 27 36 45 54 63 72 81 90 99 108 117 126 | 945
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 | 1050
0 11 22 33 44 55 66 77 88 99 110 121 132 143 154 | 1155
---------------------------------------------------------------------------
0 66 132 198 264 330 396 462 528 594 660 726 792 858 924
#include <stdio.h>
#define N 10
int main(void) {
int digit_count[N];
int x, last_digit;
while (scanf("%d", &x) == 1) {
last_digit = x % N;
digit_count[last_digit] = digit_count[last_digit] + 1;
}
last_digit = 0;
while (last_digit < N) {
printf("%d numbers with last digit %d read\n", digit_count[last_digit], last_digit);
last_digit = last_digit + 1;
}
return 0;
}
It works on the students laptop:
gcc -Wall -O last_digit.c a.out 42 121 100 11 <cntrl-d> 1 numbers with last digit 0 read 2 numbers with last digit 1 read 1 numbers with last digit 2 read 0 numbers with last digit 3 read 0 numbers with last digit 4 read 0 numbers with last digit 5 read 0 numbers with last digit 6 read 0 numbers with last digit 7 read 0 numbers with last digit 8 read 1 numbers with last digit 9 read
But when run at uni, it fails:
dcc last_digit.c a.out 42 121 100 11 <cntrl-d> 778121076 numbers with last digit 0 read 7632239 numbers with last digit 1 read -2032569224 numbers with last digit 2 read 32727 numbers with last digit 3 read 0 numbers with last digit 4 read 0 numbers with last digit 5 read -2032409578 numbers with last digit 6 read 32727 numbers with last digit 7 read -21600000 numbers with last digit 8 read 32767 numbers with last digit 9 read
Why doesn't the code work at uni?
Why doesn't dcc detect an error?
Fix the code (make sure you understand how it works - it's a common and useful programming pattern).
int nums1[10];
int nums2[] = {0,1,2,3,4,5,6,7,8,9};
int nums3[10] = {0,2,4,6,8,-2};
int nums4[10] = {0};
int nums5[2][10] = {{0,1,2,3,4,5,6,7,8,9},
{10,20,30,40,50,60,70,80,90,100}};
printf("%d\n",nums2[3]);
printf("%d\n",nums3[5]);
printf("%d\n",nums5[0][1]);
printf("%d\n",nums5[1][0]);
nums1[0] = nums2[1] + 10 ;
printf("%d\n",nums1[0]);
int i = 0;
printf("%d\n",nums1[i]);
printf("%d\n",nums2[10]);
printf("%d\n",nums5[2][0]);
printf("%d\n",nums5[1][10]);