1. Tutorial 8 Pointers and Strings
NUS School of Computing
CS1010E Programming Methodology
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2. CS1010E Tutorial Slides Prepared by Wu Chao
Quick Summary
<string.h> library:
strlen(const char* str): returns the number of characters before ‘\0’
strcmp(const char* str1, const char* str2): string comparison returns a positive number if str1 proceeds str2 and vice versa
strcat(char* str1, const char* str2): append str2 to the back of str1
Pointers and Array duality
Arr[1]  *(Arr + 1)
&Arr[1]  Arr + 1
CS1010E Tutorial Slides Prepared by Wu Chao

3. CS1010E Tutorial Slides Prepared by Wu Chao
Q1: Pointers Tracing
CS1010E Tutorial Slides Prepared by Wu Chao

4. CS1010E Tutorial Slides Prepared by Wu Chao
Q1: Pointers Tracing
int i1, i2;
int *p1, *p2;
i1 = 5;
p1 = &i1;
i2 = (*p1)/2 + 10;
p2 = p1; i1 5 i2 12 p1 p2
001
001 12
CS1010E Tutorial Slides Prepared by Wu Chao

5. CS1010E Tutorial Slides Prepared by Wu Chao
Q1: Pointers Tracing
How to print out the values for tracing in our main()?
(void *): typecast in order to prevent warning as we are printing out the address values of the memory location.
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6. Q2: Binary Search with Pointers
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7. Q2: Binary Search with Pointers3 5 7 8 9 12 15 19 21 30
Left
Mid
Right
Left
Found!
Search for: 19
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8. Q2: Binary Search with Pointers
Can we use:
mid = (right + left)/2;
Address arithmetic only allows for calculation of differences of address values
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9. Q2: Binary Search with Pointers (Optional)
Use of recursion in Binary Search
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Q3: Word Palindrome
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Q3: Word Palindrome
isPalindrome1(…)
If condition is always fulfilled till right pointer bypassed left, then it is true
If jump out of loop too early, then it is false
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12. CS1010E Tutorial Slides Prepared by Wu Chao
Q3: Word Palindrome
isPalindrome2(…)
To reverse the string, we copy from the back to the front. Initialize right to the end of the str.
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13. Q4: Get Drunk (array index simulation)
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14. Q4: Get Drunk (array index simulation)
Missing “&”: we need to pass in the address for scanf function to work, since both “numTrials” and “numSteps” are int pointers, they store the address of the variable to be scanned.
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15. Q4: Get Drunk (array index simulation)

16. Q4: Get Drunk (array index simulation)
Additional helper function:
Equal probability for the person to walk one step forward as for the person to walk one step backward.
How to perform drunken walk?
Alternatively:

17. Q4: Get Drunk (array index simulation)

18. Q4: Get Drunk (array index simulation)
Main Function:
Pass in the address of the middle element of the array declared.