Character strings in c

1. Character strings in c

2. 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.

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

4. 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);

5. char month1[ ]={‘j’,’a’,’n’,’u’,’a’,’r’,’y’}; /*String.c string variable*/ #include < stdio.h > main() { char month[15]; printf (“Enter the string”); fgets (month,8,stdin); printf (“The string entered is %s”, month); } Initializing Strings

6. 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);

7. 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);

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

9. 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"

10. 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"

11. 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

12. strlen(string)Returns the amount of characters in a string. s = "abcde";i = strlen(s); // i = 5

13. #include < stdio.h > #include < string.h > void main() { char s1[20],s2[20],s3[20]; int x,l1,l2,l3; printf(“Enter the strings”); scanf(“%s%s”,s1,s2); x=strcmp(s1,s2); if(x!=0) {printf(“\nStrings are not equal\n”); strcat(s1,s2); } else printf(“\nStrings are equal”); strcpy(s3,s1); l1=strlen(s1); l2=strlen(s2); l3=strlen(s3); printf(“\ns1=%s\t length=%d characters\n”,s1,l1); printf(“\ns2=%s\t length=%d characters\n”,s2,l2); printf(“\ns3=%s\t length=%d characters\n”,s3,l3); } /* Example program to use string functions*/

14. Converting strings to numbers • char *str1=“123.79”; • char *str2 = “3”; • float x; • int y; x = atof(str1); y = atoi(str2); Additional String functions

15. ctype.h has character handling functions • since a string is a character array, can convert to uppercase as follows: char name1[]=“Scooby”; int x; for (x=0; x <=strlen(name1); x++) name1[x] = toupper(name1[x]); uppercase

16. ctype.h has character handling functions • since a string is a character array, can convert to lowercase as follows: char name1[]=“Scooby”; int x; for (x=0; x <=strlen(name1); x++) name1[x] = tolower(name1[x]); lowercase

17. 1) Write a program that performs the following: • uses character arrays to read a user’s name from standard input (stdin) • tells the user how many characters are in their name • displays the user’s name in uppercase • displays the user’s name in lowercase • changes the user’s name to append “man” on the end – e.g. Jack becomes Jackman – and prints it out 2) Look up the strstr() function (page 196) and write a program that uses it to search for the last occurrence of a substring in a string. Print out the number of occurrences of the substring in the string. String programming assignments