First and foremost, I will manifest one of the prerequisites of Strings and pointers, Arrays, but before I commence to spiel the technical details, I want to point out the purposive of them. One: they are useful for lists of information, such as telephone numbers, grade lists etc.. Two: You need arrays in C in order to use strings, because C has no built-in string data type. Now that you have been briefed, we shall move on.
Arrays are a list of variables of the equivalent data type that are seperated by what you call "array elements". To declare an array, use the form of
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type var_name[size];Code: Select all
int arrayi[20]; e.g.
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int array1[20], array2[20];
array1 = array2; /* THIS IS WRONG */If you desire to copy one array to the other, it's essential that you copy it element by element. To copy element by element, you could dissipate your time and do
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array1[0] = array2[0];
array1[1] = array2[1];
array1[2] = array2[2];
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int i;
for(i = 0; i < 20; i++) array1[i] = array2[i];This is all that is imperative to know about arrays in regards to strings.
Strings
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First I want to properly delineate a string. A string in C is a null-terminated character array. Null being equivalent to 0. So when declaring a string array it is necessary that you assign it to be one byte larger than the string.
Due to a string being a null-terminated character array, you declare it like so
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char var_name[size];The method we will use to read in strings is the gets() function which is in the "stdio.h" header file. When you read in a string using the gets() function, you simply supply the name of the character array, without the index.
e.g.
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char string[80];
gets(string);Code: Select all
printf(string);Code: Select all
printf("%s\n", string);strlen() - returns the length, in characters, of a string. strlen() does not count the null terminator.
syntax strlen(string);
strcpy() - copies contents into variable.
syntax strcpy(to, from);
strcat() - adds contents of one string to another.
syntax strcat(to, from);
strcmp() - compares to strings.
syntax strcmp(string1, string2);
strcmp() returns 0 if the strings are the same. It returns less than 0 if string1 is less than string2. It returns greater than 0 is string1 is greater than string2.
One string is not greater than the other because it has more characters, strcmp() compares strings lexicographically, which means in dictionary order. Therefore, a string is less than another when it would appear before the other in a dictionary, and greater than when it appears after the other. The comparison is also case sensitive, lowercase being greater than uppercase.
These string-related functions are found in the "string.h" header file.
Pointers
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Ahh, C's most important, but also most troublesome feature. Pointers. A pointer is a variable that holds the memory address of another object.
e.g. If a variable called point1, contains the memory address of a variable named point2. It is said that point1 points to point2.
To declare a pointer, use the form of
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type *var_namee.g.
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int *pointC contains two special pointer operators, * and &. The & operator returns the address of the variable it precedes. The * operator returns the value stored at the address that it precedes.
Well I was expecting to write more about pointers, but I am too ridiculously lazy. Maybe I will create another tutorial that goes more in depth. Please excuse errors, this was a 20 minute tutorial :p
