1. Lecture 11: Strings
B Burlingame
11 April 2018

2. Announcements Midterm due Read chapter 9 Homework #7 due next week
Sign up for review sessions over the next week
Read chapter 9
Homework #7 due next week

3. Plan for today Review strings
Demonstrate an approach to solving Happy Numbers

4. Recall: What is an Array?
So far we've dealt with scalar variables
contain just one value
Arrays are collections of data of the same type that occupy contiguous memory locations
Individual values in the collection are called elements of the array
Need to declare before use:
#include <stdio.h>
int main() {
int i=0;
double test[4] = {0};
test[0]=95.5;
test[1]=74.0;
test[2]=88.5;
test[3]=91.0;
for(i=0; i<4; i++)
printf("test[%d]=%lf",i,test[i]);
0x%p\n",&test[i]); }
return 0;
Run array_practice2.c in ChIDE.
Format (1D array)
type array_name [num_elements];
Ex. Array of 4 doubles named, 'test'

5. Strings
Strings are encoded arrays of characters designed to hold language
Recall that all characters are encoded as numeric values
Most modern systems use a variant of ASCII or Unicode
We’ll assume ASCII

6. Strings
By convention, strings in C are a null terminated array of characters
There is no intrinsic string datatype
Null equals character value 0
i.e. char z = 0; z has a null character
written \0
Declaration: char string[] = “Hello world”;
Stored: Hello World\0 (ie 12 characters)
All string handling expects this

7. Working with strings Much like working with pointers and arrays
Many helper routines in string.h
strcmp – tests strings for equivalence
strcat – concatenates two strings
strstr – locates a string within a string
Etc.
char string[] = “Hello World”;
for( int i = 0; string[i] != 0 ; ++i ) {
if( string[i] >= ‘A’ && string[i] <= ‘Z’ )
string[i] = string[i] + (97 – 65); }

8. Comparing strings #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void) {
char name[100] = "Falken"; // String literal initialization
char input_name[100] = ""; // Empty string initialization
char buff[100] = { 0 }; // All null initialization
fgets(buff, sizeof(input_name), stdin);
sscanf(buff, "%s", input_name); // Note the lack of &
if (strcmp(input_name, name) == 0) // strcmp is in string.h, unusually
{ // strcmp returns <0, 0, or >0.
// 0 means "no difference"
printf("Hello Professor %s\n", input_name); }
else
printf("Hello %s, would you like to play a game?\n", input_name);
return(EXIT_SUCCESS);

9. References
Darnell, P. A. & Margolis, P. E. (1996) C, a software engineering approach, 3rd ed., Springer, New York, p. 327.
Visited 23OCT2010.