Let\u2019s look at this code. First we see the array \u201cprimes\u201d. It is a list of integers (type int). This array is already initialized with values.<\/p>\n
int primes[] = {2,3,5,7,11,13,17,19,23,29};<\/pre>\nThese integer values will be stored adjacent to each other in memory. If the size of an int is 4 bytes (on a 32bit microcontroller), the the array will occupy a block of 40 bytes.<\/p>\n
Next, we iterate through and read the values in the array using a for-loop:<\/p>\n
for (unsigned int n=0; n<10; n++) {\r\n printf(\"%dth Prime is %d\\n\", n, primes[n]);\r\n}<\/pre>\nFor each value of n, we read the ![\"n^{th}\"](\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/ql-cache\/quicklatex.com-2abf0b71b2242df3a72e948f3e5c9ea0_l3.png\" "\\"Rendered")
value primes[n].<\/p>\n
Consider a more complex example now:<\/p>\n
#include <stdio.h>\r\n#include <math.h>\r\n\r\n#define N 1000\r\n\r\ndouble x1[N];\r\ndouble x2[N];\r\ndouble delta[N];\r\n\r\n\/\/Initial values - make these very similar\r\ndouble initialValue1 = 0.3;\r\ndouble initialValue2 = 0.299999999;\r\n\r\n\/\/The parameter r, set to generate a chaotic sequence\r\ndouble r= 4.0;\r\n\r\nint main() {\r\n \r\n \r\n \/\/******************************************\r\n \/\/Let's generate a chaotic sequence of data!\r\n \/\/******************************************\r\n \/\/ https:\/\/en.wikipedia.org\/wiki\/Logistic_map\r\n \r\n \/\/Start with very similar initial conditions\r\n x1[0] = initialValue1;\r\n x2[0] = initialValue2;\r\n delta[0] = 0.0;\r\n \r\n \/\/Calculate values for n=1..99 and any differences \r\n\t\/\/using the same \"logisic map\" function\r\n for (unsigned int n=0; n<(N-1); n++) {\r\n x1[n+1] = r*x1[n]*(1.0-x1[n]);\r\n x2[n+1] = r*x2[n]*(1.0-x2[n]);\r\n delta[n+1] = x1[n+1] - x2[n+1];\r\n }\r\n \r\n \/\/Write results\r\n for (unsigned int n=0; n<N; n++) {\r\n printf(\"n=%d\\t%8.6f\\t%8.6f\\tDIFFERENCE=%8.6f\\n\", n, x1[n], x2[n], delta[n]);\r\n }\r\n \r\n return 0;\r\n}<\/pre>\nFirst of all, we define N as an alias for 1000<\/p>\n
#define N 1000<\/pre>\nNow we create three arrays of type double<\/span>\u00a0.<\/p>\ndouble x1[N];\r\ndouble x2[N];\r\ndouble delta[N];<\/pre>\nEach of these is a distinct block of memory, size N*sizeof(double)<\/span>\u00a0. The first values each array is then initialised:<\/p>\nx1[0] = initialValue1;\r\nx2[0] = initialValue2;\r\ndelta[0] = 0.0;<\/pre>\nNote that the index (value in square brackets) starts at zero for C and C++ arrays.<\/p><\/blockquote>\n
For the curious, we see initialValue1<\/span>\u00a0 and initialValue2<\/span>\u00a0 have very similar values as this is a demonstration of \u201cchaotic behavior\u201d).<\/p>\nNext we once again use a for-loop to iterate, calculate some values and store results in the arrays:<\/p>\n
for (unsigned int n=0; n<(N-1); n++) {\r\n x1[n+1] = r*x1[n]*(1.0-x1[n]);\r\n x2[n+1] = r*x2[n]*(1.0-x2[n]);\r\n delta[n+1] = x1[n+1] - x2[n+1];\r\n }<\/pre>\nThe value of n ranges from 0 to 98. Once the arrays are full, we write the values to the terminal:<\/p>\n
for (unsigned int n=0; n<N; n++) {\r\n printf(\"n=%d\\t%8.6f\\t%8.6f\\tDIFFERENCE=%8.6f\\n\", n, x1[n], x2[n], delta[n]);\r\n}<\/pre>\nNote the data types:<\/p>\n
![\"\"](\"http:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/uploads\/sites\/94\/2018\/10\/arraysDataType.png\")
<\/p>\n
When we use square brackets to access the value in an array, such as x[n]<\/span>\u00a0, we say we are dereferencing<\/em> the array.<\/p>\nWhen we write the array name without any square braces, we get the memory address of the first element in the array. This is also known as a reference<\/em> to the first element of the array. Therefore we call x1<\/span>\u00a0 a reference type.<\/p><\/blockquote>\n <\/p>\n","protected":false},"excerpt":{"rendered":"
In C and C++, and array is a block of memory reserved to hold an ordered list of data of the same type. This could be a list of type int, float, double etc.. It can also be a list of other arrays, or more complex types such as structures and unions. For example: #include… Continue reading Array – (Glossary Entry)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":153,"menu_order":62,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-538","page","type-page","status-publish","hentry","entry"],"_links":{"self":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/538","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/comments?post=538"}],"version-history":[{"count":1,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/538\/revisions"}],"predecessor-version":[{"id":540,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/538\/revisions\/540"}],"up":[{"embeddable":true,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/153"}],"wp:attachment":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/media?parent=538"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}