Exercise: Variables in C – Introduction to C Programming for Embedded Devices

The real thing (0.5p)¶

Describe how C variable int32_t luku = -345; would be stored in to an 8-bit memory.

Use the following format in your answer, and use as many memory locations as needed. Addresses start from zero and both address (4 bits) and value (8 bits) are given as binary numbers.

memory_address:value

You must write one line for each memory address.

Example. Variable uint8_t example = 9; would be stored in this memory followingly:

0000:00001001

You have only 5 attempts to answer correctly this question.

Choosing Memory-Efficient Variable Types (0.75)¶

In C, the amount of memory occupied by some variable types depends on the compiler and target architecture.

Consider the following program:

#include <stdio.h>

int main(void) {
    printf("Size of char: %zu bytes\n", sizeof(char));
    printf("Size of signed char: %zu bytes\n", sizeof(signed char));
    printf("Size of unsigned char: %zu bytes\n", sizeof(unsigned char));
    printf("Size of short int: %zu bytes\n", sizeof(short int));
    printf("Size of unsigned short int: %zu bytes\n", sizeof(unsigned short int));
    printf("Size of int: %zu bytes\n", sizeof(int));
    printf("Size of unsigned int: %zu bytes\n", sizeof(unsigned int));
    printf("Size of signed long int: %zu bytes\n", sizeof(signed long int));
    printf("Size of unsigned long int: %zu bytes\n", sizeof(unsigned long int));
    printf("Size of float: %zu bytes\n", sizeof(float));

    return 0;
}

When compiled and executed on the computer used for this exercise, the program produces:

Size of char: 1 bytes
Size of signed char: 1 bytes
Size of unsigned char: 1 bytes
Size of short int: 2 bytes
Size of unsigned short int: 2 bytes
Size of int: 4 bytes
Size of unsigned int: 4 bytes
Size of signed long int: 8 bytes
Size of unsigned long int: 8 bytes
Size of float: 4 bytes

Each variable below may contain any value between the given minimum and maximum.

Declare each variable using the variable type that occupies the least possible amount of memory while still being able to represent the complete range of values.

Variable	Minimum value	Maximum value
a	'A'	'Z'
b	0	255
c	-129	127
e	-32769	32767
f	-2147483649	2147483647
g	-3.14	3.14

For this exercise:

Do not use types from <stdint.h>, such as int8_t, uint8_t, int16_t, or uint16_t.
Remember to use adequate keywords when needed: short, long, signed...
Write only the variable declarations. Do not initialize the variables.
Write one declaration per line. Do not leave blank lines or whitespaces

For example:

int a;
long int b;

Mysteries of C variables (0.25p)¶

Which of the following statements are true? You have only 5 attempts to answer, so please, think carefully your answers.

extern int x; is a declaration of x, but it does not define the variable or allocate storage for it.

int x = 5; is simultaneously a declaration, a definition, and an initialization of x.

If x has already been defined, the statement x = 10; initializes x again.

In int values[] = {1, 2, 3}; the compiler can determine the size of the array from the initializer.

char message[] = "Hello";creates an array with five elements because the string contains five visible characters.

When a value does not fit in the destination integer type, the compiler always stops compilation with an error.

Casting is an explicit conversion written by the programmer, for example (double)x. Promotion is an automatic conversion performed by C when evaluating an expression, for example when a smaller integer type is promoted before an arithmetic operation.

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Lovelace

Variables in C¶

The real thing (0.5p)¶

Choosing Memory-Efficient Variable Types (0.75)¶

Mysteries of C variables (0.25p)¶

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