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(a) Create
appropriate declarations for each of the following variables: |
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Definitions
of various C types: |
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(i) digits, an array of 10 integers. |
[1] |
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int digits[10]; |
[1] |
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(ii) rates, an array of 6 floats. |
[1] |
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float rates[6]; |
[1] |
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(iii) apc, an array of 20 pointers to
characters. |
[1] |
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char *apc[20]; or char
*(apc[20]); Note: the [ ] have higher precedence that *, so in the absence of parentheses,
the array descriptor is applied first then the pointer descriptor. |
[1] |
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(iv) pacc, a pointer to an array of 20
characters |
[2] |
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char (*pacc)[20]; or
char pacc[ ] [20]; |
[2] |
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(b) What is printed
when the following program is executed? |
[4] |
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The
following will be printed: |
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p1 is 2 |
[1] |
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p2 is 30 |
[1] |
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p3 is 30 |
[1] |
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p4 is 3 |
[1] |
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If the
students omit the p1 is . . ., but give the correct numerical values of p1, etc., then
award the marks as above. |
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(c) The following
function is supposed to find the average mark from an array of n marks in the range 0 to
100. Find, and correct the seven errors in its definition: |
[7] |
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Errors in the
definition of averageMark: |
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real is not a
valid type in C. It should be float or double. |
[1] |
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sum is not
initialised to zero. |
[1] |
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Commas in the
for statement instead of semi-colons. |
[1] |
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The
auto-increment should be written as += and not =+ |
[1] |
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The starting
index for the for-loop should be 0, |
[1] |
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and the
termination condition for the for-loop should be i<n. |
[1] |
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Alternatively,
give 2 marks if the student changes the use of the index to marks [i - 1]. |
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The coercion
double should be in brackets. |
[1] |
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Therefore a
program such as the above below should be awarded seven marks: |
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(d) Write a function
istriangle that takes three integers as its arguments, each representing the length of one
of the sides of a triangle. The function should return 1 if the numbers form a valid
triangle and 0 otherwise. Hint: the sum of any two sides must be
greater than the third side. |
[4] |
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The students
may have produced any of the following answers for the definition of istriangle. Give full
marks (4 marks) if they use either the first or second definitions shown below. A maximum
of three marks can only obtained if their answers are similar to the third and fourth
function below. |
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(i)
Possible answer one: |
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[4
marks] |
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(ii)
Possible answer two: |
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[4
marks] |
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(iii)
Possible answer three: |
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[3
marks] |
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(iv)
Possible answer four: |
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[3
marks] |
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