Learn C Programming Lesson 7 String

Learn C Programming Lesson 7 - Strings

A string is an array of characters. Strings must have a 0 or null character after the last character to show where the string ends. The null character is not included in the string.

There are 2 ways of using strings. The first is with a character array and the second is with a string pointer.

A character array is declared in the same way as a normal array.

char ca[10];

You must set the value of each individual element of the array to the character you want and you must make the last character a 0. Remember to use %s when printing the string.

char ca[10];
ca[0] = 'H';
ca[1] = 'e';
ca[2] = 'l';
ca[3] = 'l';
ca[4] = 'o';
ca[5] = 0;
printf("%s",ca);

String pointers are declared as a pointer to a char.

char *sp;

When you assign a value to the string pointer it will automatically put the 0 in for you unlike character arrays.

char *sp;
sp = "Hello";
printf("%s",sp);

You can read a string into only a character array using scanf and not a string pointer. If you want to read into a string pointer then you must make it point to a character array.

char ca[10],*sp;
scanf("%s",ca);
sp = ca;
scanf("%s",sp);

String Handling Functions:
The strings.h header file has some useful functions for working with strings. Here are some of the functions you will use most often:

strcpy(destination,source)
You can't just use string1 = string2 in C. You have to use the strcpy function to copy one string to another. strcpy copies the source string to the destination string.

s1 = "abc";
s2 = "xyz";
strcpy(s1,s2); // s1 = "xyz"

strcat(destination,source)
Joins the destination and source strings and puts the joined string into the destination string.

s1 = "abc";
s2 = "xyz";
strcat(s1,s2); // s1 = "abcxyz"

strcmp(first,second)
Compares the first and second strings. If the first string is greater than the second one then a number higher than 0 is returned. If the first string is less than the second then a number lower than 0 is returned. If the strings are equal then 0 is returned.

    s1 = "abc";
    s2 = "abc";
    i = strcmp(s1,s2); // i = 0

strlen(string)
Returns the amount of characters in a string.

s = "abcde";
i = strlen(s); // i = 5

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