1. CS1010 Discussion Group 11
Week 4 – Overview of C programming

2. Slides are at http://www.comp.nus.edu.sg/~yanhwa/
HELLO!
Slides are at

3. Have you submitted your Lab #1?Do
Follow Instructions
Give meaningful names for variables
Appropriate commenting
Must do
Double/triple check your indentation (gg=G in vim will auto-indent your program nicely!)
Add header comment, check skeleton code given.
Do not
Forget to initialise variables whenever necessary
Output format does not conform to requirement
Follow lab guidelines

4. What are “preprocessor directives”?
Lecture Summary
What are “preprocessor directives”?
What is stdio.h?
Why is it useful to use a macro expansion?
#define, #include
scanf, printf
"%7d%s %c%lf"
What is an escape sequence?
The above format string scans the first seven characters as a decimal integer, then reads the remaining as a string until a space, new line or tab is found, then scans the first non-whitespace character following and a double-precision floating-point number afterwards.
The C preprocessor modifies a source file before handing it over to the compiler
The `#include' directive works by directing the C preprocessor to scan the specified file as input before continuing with the rest of the current file.

5. Typecasting (implicit vs explicit)
Lecture Summary
Typecasting (implicit vs explicit)
float a = 10 / 3
float a = (float) (10/3)
float a = (float) 10 / 3
float a = 10.0 / 3
The above format string scans the first seven characters as a decimal integer, then reads the remaining as a string until a space, new line or tab is found, then scans the first non-whitespace character following and a double-precision floating-point number afterwards.

6. How to use maths functions?
Lecture Summary
How to use maths functions?
Include <math.h> AND
Compile your program with –lm option (i.e. gcc –lm …)
The above format string scans the first seven characters as a decimal integer, then reads the remaining as a string until a space, new line or tab is found, then scans the first non-whitespace character following and a double-precision floating-point number afterwards.

7. Lab
CodeCrunch Lab #1
Have you submitted?

8. Tutorial 2 Q2b
Superfluous and incorrect comments
Inconsistent spacing and indentation
Redundant statement (where?)

9. Tutorial 2 Q3b
The value of num1 will be displayed as instead of
Not all numerical values can be represented accurately in a computer, due to the finite number of bits used to represent a value.
IEEE 754 Floating-Point Representation (not in CS1010, see CS2100)
Double can only try to improve accuracy

10. Tutorial 2 Q4
Did you run the program?
Inf (Infinity)
NaN (Not a Number)
Why do you get a “core dump”?

11. Tutorial 2 Q5
Explain a++ vs ++a.
a++ or a-- is postfix operation - the value of a will get changed after the evaluation of expression.
++a or --a is prefix operation - the value of a will get changed before the evaluation of expression
Redundancy again

12. countNeg  0 Tutorial 1 Q4a Why must we initialise in this case?
for k from 1 to N
if (a[k] < 0)
countNeg  countNeg + 1;
print countNeg
Why must we initialise in this case?

13. Restricted to only numerical values
Tutorial 2 Q6
num1 = num1 – num2;
num2 = num1 + num2;
num1 = num2 – num1;
Restricted to only numerical values
Risks overflow (what is overflow?) Max integer is 2^31 -1
Not general
Extra time: explain overflow in

14. Functions
printf and scanf are standard library functions
the main() function will return 0 to the unix environment, indicating success
Functions have input (arguments) and output (return value)
f(x) = x^2 in maths also has an input and output
How do we define our own function?

15. Functions /* function prototype */
int max(int num1, int num2); // good practice to include names of parameters
int main (void) {
/* local variable definition */
int a = 100;
int b = 200;
int ret;
/* calling a function to get max value */
ret = max(a, b);
printf( "Max value is : %d\n", ret );
return 0; }

16. Functions /* function returning the max between two numbers */
int max(int num1, int num2) {
/* local variable declaration */
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result; }

17. Functions and call stack https://www.youtube.com/watch?v=jRcll9qY6b 0
Functions call stack
Functions and call stack 0

18. FreezerV2

19. Freezer v2 //Freezer temperature after t time #include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(void){
float temp, t = 0;
float hours = 0, mins = 0;
printf("Enter hours and minutes since power failure: ");
scanf("%f %f", &hours, &mins);
t = hours + mins/60;
temp = (4 * pow(t, 10))/(pow(t, 9) + 2) - 20;
printf("Temperature in freezer = %.2f\n", temp);
return 0; }
Freezer v2