1CSSE 332Structures, Command Line Arguments, File Reading, and Functions2 Multi-dimensional arraysint points[3][4];points [1][3] = 12; /* NOT points[3,4] */printf(“%d”, points[1][3]);Multi-dimensional Arrays3Example 6:#include <stdio.h>struct birthday{int month;int day;int year;}; //Note the semi-colonint main() {struct birthday mybday; /* - „new‟ not needed ! *//* otherwise, it‟s just like Java ! */mybday.day=1; mybday.month=1; mybday.year=1977;printf(“I was born on %d/%d/%d\n”, mybday.day,mybday.month, mybday.year);}Structures Approximation of Java’s classes with only data encapsulation (no methods)4More on Structuresstruct person{char name[41];int age;float height;struct { /* embedded structure */int month;int day;int year;} birth;};struct person me;me.birth.year=1977;………/* array of info about everyone in class */struct person class[60]; class[0].name=“Frank”; class[0].birth.year=1971;……5typedef typedef struct person myPerson– Defines a new type name myPerson as a synonym for type struct personint main(){myPerson me;me.age = 6;…}6User-defined header files Structures and other data structures may be defined in a header file, for better organization of the code. These are user-defined header files e.g. person.h To include it:#include “person.h’’ at the start of the program file.7Command line arguments Accept input from the command line main(int argc, char* argv[])– argc – argument count– argv[] – value of each argument8Example 7#include <stdio.h>int main(int argc, char *argv[]){int count = 0;if(argc < 2){printf("Must enter at least one argument\n");printf("Example: ./a.out this is program 7\n");exit(1);}printf(" The number of arguments is %d\n", argc);printf("And they are :\n");while(count < argc){printf("argv[%d]: %s\n",count,argv[count] );count++;}printf("\n");return 0;}9File handling Open a file using “fopen” Returns a FILE pointer which is used to access the file. Modes:– Read(r) – Opens file for reading. Returns error (NULL) if file does not exist. – Write(w) – create a new file for writing (overwrite old one). File pointer at the beginning of file.– Append(a) – create a new file if file does not exist. Preserve the contents if file does exist and pointer at the end of the file. fprintf, fscanf, fclose10Example 8#include <stdio.h>int main(int argc, char *argv[]){/* Declare a file pointer */FILE *inFile=NULL; /* open file for writing*/inFile = fopen(“test.txt”, “w”);/* need to do explicit ERROR CHECKING */if(inFile == NULL){exit(1);}/* write some data into the file */fprintf(inFile, “Hello there\n”);/* don‟t forget to release file pointer */fclose(inFile); return 0;}11Reading till end of file int feof(FILE *) – The function is defined in stdio.h– Returns a non-zero value (TRUE) if end of file has been reached, and zero otherwise. Sample code:fscanf(inFile, "%d", &int1); // Try to read from fileprintf("%d \n", int1); //Do something with the datawhile (feof(inFile) == 0 ){ //If there is data, enter loopfscanf(inFile, "%d", &int1); //Try reading again printf("%d \n", int1); //Do something with the data} //go back to while to test if end of file has been reached12Functions - why and how ? If a problem is large Modularization –easier to: • code• debug Code reuse Passing arguments to functions– By value Returning values from functions– By value13Functions – basic exampleExample 9#include <stdio.h>/* function prototype at start of file */int sum(int a, int b); int main(int argc, char *argv[]){int total = sum(4,5); /* call to the function */printf(“The sum of 4 and 5 is %d\n”, total);}/* Arguments for the function are passed by value*/int sum(int a, int b){return (a+b); /* return by value */}14Memory layout and addresses5 10 12.5 9. 8 r sint x = 5, y = 10;float f = 12.5, g = 9.8;char c = „r‟, d = „s‟;4300 4304 4308 4312 4316 4317x y f g c dHomework 4 Continue working on lab
View Full Document
Unlocking...