1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger
Fall 2018
Lecture 24
Character arrays and strings (continued)

2. ECE Application Programming: Lecture 24
Lecture outline
Announcements/reminders
Program 5 due 11/7
Exam 2 in class Monday, 11/5
Will be allowed one 8.5” x 11” note sheet
Will cover lectures (except lecture 16)
Lec. 25: Exam 2 Preview (Fri. 11/2)
Today’s lecture
Review: String basics
String functions
7/3/2019
ECE Application Programming: Lecture 24

3. ECE Application Programming: Exam 2 Preview
Review: strings
Represented as character arrays
Can be initialized using string constants
char hello[] = “Hello”;
Can access individual elements
hello[3] = ‘l’;
Can print directly or with formatting
Print directly: printf(hello);
Print w/formatting using %s: printf(“%s\n”, hello);
Reading strings: scanf(“%s”, str);
Reads all characters up to (but not including) first space, tab, or newline
Must leave enough room for terminating ‘\0’
7/3/2019
ECE Application Programming: Exam 2 Preview

4. ECE Application Programming: Lecture 24
String functions
Things we’d like to do with strings:
Set one equal to another
Compare two strings
Find # characters in string
String may not fill array (“buffer”) allocated for it
“Add” two strings together
“abc” + “def” = “abcdef”
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ECE Application Programming: Lecture 24

5. String functions (cont.)
In <string.h> library:
Copying strings:
char *strcpy(char *dest,
const char *source);
char *strncpy(char *dest,
const char *source,
size_t num);
Return dest
Does not append ‘\0’ unless length of source < num
Comparing strings:
int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t num);
Character-by-character comparison of character values
Returns 0 if s1 == s2, >0 if s1 > s2, <0 if s1 < s2
7/3/2019
ECE Application Programming: Lecture 24

6. String functions (cont.)
Find # of characters in a string
size_t strlen(const char *s1);
Returns # characters before ‘\0’
Not necessarily size of array
“Add” strings together—string concatenation
char *strcat(char *dest,
const char *source);
char *strncat(char *dest,
const char *source,
size_t num);
Returns dest
7/3/2019
ECE Application Programming: Lecture 24

7. ECE Application Programming: Lecture 24
Example: Strings
What does the following program print?
int main() {
char s1[15];
int n1;
char s2[10] = “.216”;
int n;
strncpy(s1, “16”, 15);
n1 = strlen(s1);
printf(“s1 = %s\n”, s1);
printf(“Length of s1 = %d\n\n”, n1);
printf(“%c\n\n”, s1[1]);
strncat(s1,s2,10); n1 = strlen(s1); printf(“s1 = %s\n”, s1); printf(“Length of s1 = %d\n\n”, n1); // Assume user inputs: ABC ABD printf(“Enter two strings:”); scanf(“%s%s”, s1, s2); n = strncmp(s1, s2, 15); if (n > 0) printf(“%s > %s\n”, s1, s2); else if (n < 0) printf(“%s < %s\n”, s1, s2); else printf(“%s == %s\n”, s1, s2); return 0; }
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ECE Application Programming: Lecture 24

8. ECE Application Programming: Lecture 24
Example solution
s1 = 16 Initial value of s1 Length of s1 = 2 6 s1[1] s1 = s1 after strncat() Length of s1 = 6 Enter two strings: ABC ABD ABC < ABD Result of strncmp()
7/3/2019
ECE Application Programming: Lecture 24

9. ECE Application Programming: Lecture 24
Final notes
Next time
Exam 2 Preview
Reminders:
Program 5 due 11/7
Exam 2 in class Monday, 11/5
Will be allowed one 8.5” x 11” note sheet
Will cover lectures (except lecture 16)
Lec. 25: Exam 2 Preview (Fri. 11/2)
7/3/2019
ECE Application Programming: Lecture 24