CISC 130: Today’s Class

1. CISC 130: Today’s Class • Recap • Files, writing files • 1D Array Recap • 2D Arrays • Assignment 11 • Searching for a string R. Smith - University of St Thomas - Minnesota

2. Recap • Drawing in 2 dimensions • Vertical Histogram • Working with Files R. Smith - University of St Thomas - Minnesota

3. Recap: Working with files • Instead of getchar(), putchar(), printf() • Use getc(), putc(), fprintf() • “FILE” type variable with weird syntax • Function fopen() opens a file • First argument: string with file name • Second argument: “r” for read, “w” for write • Result: “FILE pointer” if success, else “NULL” literal value • Function fclose(fp) called when done R. Smith - University of St Thomas - Minnesota

4. Example: Writing a File FILE *fp; // file pointer char lin[LEN]; // line buffer inti; // loop index printf("file name: "); getline(lin, LEN); fp = fopen(lin, "w"); for (i = 0; i < 10; i++) fprintf(fp, "Line %d\n", i); fclose(fp); R. Smith - University of St Thomas - Minnesota

5. Writing a File • Using putc(c, fp) to write characters • First argument: char; second argument: file pointer • Asking for a file name • It goes to the same folder unless you type in a different folder • You should check for • Bad file name – what happens? • Handling the error condition • File name loop • Write a do or while loop to repeat till the fopen() works • Retrofitting an Existing Program • Convert ‘histogram’ to print to a file • Or, convert your paystub printer to go to a file R. Smith - University of St Thomas - Minnesota

6. Checklist for Side Effects • Does it do input (from keyboard, for example)? • Does it do output (to display, for example)? • Does it modify its arguments (arrays)? • Any YES to the above => side effects • OK to “look” at arrays, but not to change them • Changing an array argument = Side Effect R. Smith - University of St Thomas - Minnesota

7. Recap on 1D Array functions • There’s the ‘maximum’ length and ‘real’ length • Maximum length = the most elements it can possibly hold • Real length = actual number of elements in the array • When we DECLARE the function • The array argument: • We specify the array Type and Size: intnums[NSIZE] • We may have a separate argument for the ‘real’ length • When we USE the function • The array argument: • We specify JUST THE ARRAY NAME, no size or index • If we have a separate ‘length’ argument, it’s given as an integer R. Smith - University of St Thomas - Minnesota

8. Using Arrays • For 1D arrays, there are TWO Cases: • Case #1: doing something to an ELEMENT • We have a single item in the array we need to work on • We include its INDEX (in brackets: num[i]) to pick it out • Case #2: working on the Whole Array • Always done by a Function • We pass the Array Name Only to the function • Just for old times’ sake, write a ‘sum’ function R. Smith - University of St Thomas - Minnesota

9. Two dimensional arrays • Declare with two indices • First one selects the row • Second index selects the column • Square brackets around each index: a[1][2] • For a list of strings • First index picks a string • Second index is a character in that string R. Smith - University of St Thomas - Minnesota

10. 2D Arrays and Functions • Function doesn’t need size of first index • Function does need size of other indices • Must appear in argument declaration • Write a sample program that fills in a string array R. Smith - University of St Thomas - Minnesota

11. Assignment 11 • Number lookup program • Functions • Read a file of name/number pairs into arrays • Extract strings from strings • Search the array for a name typed in • Read a line of text from a file • Compare the “prefix” of a string • Main loop R. Smith - University of St Thomas - Minnesota

12. Suggested Strategy • Phase 1 • Write a function to read strings into an array • A sentinel loop, looks for ‘null’ line • Write a function to print strings from an array • Can take • Call them from main • Phase 2 • Write a ‘split’ function to split lines • Rewrite the ‘read’ function to call the ‘split’ function • Phase 3 • Have it read the data from a file R. Smith - University of St Thomas - Minnesota

13. Let’s work on Phase 1 • What variables? • What functions? R. Smith - University of St Thomas - Minnesota

14. Standard string.h functions • strcmp() – described yesterday • Input: 2 strings • Output: neg, zero, pos = difference between mismatch • strspn() – skips over a set of chars • Input1: string to check • Input2: string of chars to skip over • Output: offset to first char that’s not in Input2 • strncpy() – copies a string to a destination • Input1: destination • Input2: source • Input3: size of destination • strlen() – length of a string R. Smith - University of St Thomas - Minnesota

15. Writing the extract() function • We need 2 array indices • We need a variable for the ‘split’ index • First, find the split point • Next, copy the number and mark the end • Finally, copy the name using the 2 indices R. Smith - University of St Thomas - Minnesota

16. How the assignment works • Call a function to read the number/name strings into 2 separate arrays • One keeps the name strings • One keeps the number strings • Name[i] is the person whose number is in number[i] • Do a loop till a blank line is entered • Read a line from input • Look it up in the ‘names’ array; retrieve the index • If it’s a valid index, print out the name and number • Start with typed-in numbers/names • Create a file of numbers/names for next step R. Smith - University of St Thomas - Minnesota

17. The extract() function void extract (char str[], char name[], char number[]) { inti, j; // indices to copy name int split; // split point between name and number split = strspn(str, "01234567890- "); strncpy(number, str, SIZE); number[split] = '\0'; j = 0; i = split; while (str[i] != '\0') { name[j] = str[i]; j = j + 1; i = i + 1; } name[j] = '\0'; } R. Smith - University of St Thomas - Minnesota

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