C Flashcards

Question

What makes a good variable name?

Answer 1

Must start with _ or character. | Can have uppercase lowercase or numbers

Answer 2

for a double using %.2e would give it to 2 decimal places

Answer 3

Changing their data type. If you wanted to perform floating point division with integers float answer answer=(float)value1/(float)value2;

Answer 4

A program within a compiler that pauses a program and analyses what's going on.

Answer 5

Increment. Add 1 to the value. Whether it is in front of a variable or after it matters.

Answer 6

answer=20%3; | Would return a value of 2 as it gives the remainder when 20 is divided by 3.

Answer 7

time=time*hours

Answer 8

#include header

Answer 9

sqrt(x) | math header needed

Answer 10

pow(x,3) gives x*x*x | don't use ^

Answer 11

%lf or %le for doubles %f for float %d for integer

Answer 12

``` Used to make small functions or values #define square(x) x*x #define absolute_zero -273 ```

Answer 13

Not equal to

Answer 14

one can happen, or the other but not both

Answer 15

Use [ ] | int x, values[]={10,20,30,40,50,60,70,80};

Answer 16

int multi[3][5]; | This gives 3 columns and 5 rows.

Answer 17

Measure the length of a string

Answer 18

puts the contents of string 2 into string 1

Answer 19

Purpose: Detects whether two strings are the same. Returns: (s==0) if the two strings are identical, (s<0) if str1 is alphabetically lower than str2 (s>0) if str1 is alphabetically greater than str2.

Answer 20

Purpose: Detects whether str2 occurs within str1 (e.g. house and us). Returns: (t==0) if str2 does not occur within str1, (t!=0) if str2 does occur within str1. Remember to declare t as: int *t;

Answer 21

char string [20]; scanf("%s",string); Notice that a & is not needed.

Answer 22

No value is returned to the program. | Other wise the data type that is being returned would be put there.

Answer 23

Because the array used in the main program and the function is the same and not just a copy.

Answer 24

Exist only inside the function that created them

Answer 25

Created once and can be accessed by any function comprising the program. They aren't in any main program, there aren't present in {} Difficult to debug and to use when many programmers are working on the same program

Answer 26

Write the function definition before the main program and then repeat it and the actual function at the end of the main program, so the main program knows that it exists. The wording of the function can be in a different file even.

Answer 27

Any sequence of instructions to produce any results or to perform any operations.

Answer 28

To declare a pointer with name in_file | FILE* in_file;

Answer 29

``` in_file = fopen("my_file.dat", "r"); in_file is the pointer name fopen is the function my_file.dat is the file r is what you want to do with the file ```

Answer 30

“r” – Opens an existing text file for reading starting at the beginning of the file. “w” – If the file does not exist, it creates a new text file for writing, - it deletes the current file if it already exists. “a” – Create a new text file for writing, or write at the end of an existing one. A “b” may also be used in combination with these access modes (eg. “rb”, “wb”, “ab”) which indicates that a binary file is to be opened.

Answer 31

Needs to be closed to put the changes you made onto the disk. fclose(in_file); closes the file with the pointer in_file

Answer 32

``` Use the function getc. This gives 1 character. To get more use a loop. int ch; FILE *in_file; . . ch=getc(in_file); ```

Answer 33

``` int ch; while ((ch = getc(in_file)) != EOF) { ...... } When it gets to the end of the file getc will return EOF to show the end ```

Answer 34

``` int ch; FILE *out_file; . . putc(ch,out_file); Here putc has put a single character into out_file ```

Answer 35

The function fgets() reads a string of characters from a file into a character array until a newline character is read, an end of file is reached, or until n characters have been read.

Answer 36

``` char buffer [100]; int n; FILE* in_file . . fgets(buffer,n,in_file); for long line n is the size of the blocks it reads it in ```

Answer 37

Work in the same way as printf and scanf but they input and output with files. Work with text not binary

Answer 38

do { } while (.....);

Answer 39

4, 4 and 5. | It will always round down.

Answer 40

Copies b to a, then adds one to b

Answer 41

Prototypes

Answer 42

When you want to do the work of many if...else clauses.

Answer 43

``` scanf("%d",&menu); switch (menu) { case 1: result=number1+number2; break; case 2: result=number1-number2; break; case 3: result=number1*number2; break; default: printf("Invalid operator \n”); result = 0; break; } Only integers and characters can be used for cases. The default clause is optional ```

Answer 44

Only char and int. | Same for !=

Answer 45

32 bit so 4 bytes, meaning 4 address are needed.

Answer 46

32 bits, range of ±10^+38 | Typically 3 d.p

Answer 47

64 bits, range of ±10^+308 | Typically 9 d.p

Answer 48

They might have very small differences e.g. be 8.0000000001 or 7.9999999999. Thus do if (fabs(a-b) < DIFF) /* If a and b are equal */ In the above program, two floating point values are regarded as equal if their difference is less than 10^-8

Answer 49

32 bit integer with a range of 0-2^32 (unsigned long int) or ±2^31 (signed long int)

Answer 50

16 bit integer (same pattern as long int)

Answer 51

The char datatype is used to represent characters, but we can also use it to store any 8-bit value:

Answer 52

``` & and | or ^ excusive or ~ Inverts all the bits < will shift bits to the left or right depending on the number and direction ```

Answer 53

``` All the bits in p are OR-ed with all the bits in q, result stored in r Invert all the bits in p and store the result in s Take all the bits in p and shift them by two bits to the left ```

Answer 54

3 and 2 | int will always round down.

Answer 55

The order in which statements are executed in C

Answer 56

Selection chooses which set of program lines to execute depending on the result of some conditional statement. This enables programs to make decisions about program flow. If and switch are examples

Answer 57

Iteration repeatedly executes a number of C program lines until some condition is met – these are referred to as “loops”.

Answer 58

. Checking or enforcing that values are entered by the user are in a certain range

Answer 59

reading and writing blocks of binary data | to a binary file

Answer 60

In a library

Answer 61

buffer – the array to be used to read the binary data into sizeof(int) - sizeof is a special operator which works out the memory used by each data type. We will look at this further in Lecture 9. n – the number of data items to read in in_file – the file pointer of the file to be read from

Answer 62

int nread, buffer[100]; FILE *out_file; . . fwrite(buffer, sizeof(int), n, out_file); In this example, a block of n integers stored in the array buffer[] is written to the file. The function returns the number of data items written to the file that will be n if the write is successfully performed.

Answer 63

if ((input_file = fopen(filename,"r"))==NULL) | printf("file open failed ");

Answer 64

Unlike the other file reading functions, fgets returns NULL when the end of the file is reached. Other file read functions usually return EOF upon end-of-file.

Answer 65

characters from the file pointed by fp are being put in buffer in a group of length=MAX_LENGTH

Answer 66

fputs takes a string array and outputs it to a file.

Answer 67

the string out_string and the integer i are read out from the file output_file

Answer 68

fscanf() returns either the number of separate items read during (in this case there will be 2 items corresponding to the string and the integer) or an end of file value (EOF).

Answer 69

Check that the file opened by seeing if fopen(...)==0

Answer 70

Splitting up a program into a collection of functions each of which performs a separate part of the total task

Answer 71

Happens to array arguments, where it is the same in the function and main program

Answer 72

``` the no. of columns but not the no. of rows. int add2darray(int array[][5], int nrows) ```