C Programming in Linux Jacob Chan

C/C++ and Java  Portable  Code written in one system and works in another  But in C, there are some libraries that need to be run on a certain environment  Pthred not in Windows  Similarity in programming syntax  Looping, conditionals, switches, functions, arrays, declarations/assignments (different in C, but almost similar in C++)

Differences Between C/C++ and Java  C is faster  JVM has a write-once, read anywhere code (this adds overhead)  Games are usually written in C/C++  Java is easier to learn  C/C++ is hard to grasp because of POINTERS!  Java uses pointers, but they are blackboxed  Every object in Java is a pointer  Alternative to Java: C#

Differences Between C/C++ and Java  C/C++ is more prone to runtime errors  Declaring new variables in C/C++ usually has garbage values  In Java, they are automatically set them to 0, null, or default value  POINTERS  Segmentation faults  Memory allocation is sometimes manually set by programmer  a[10] with 5 elements will return garbage values for the next 5  Memory errors will print out a segmentation fault error  Effect: CRASH!!

Differences Between C/C++ and Java  Object-oriented-ness of Java  Java is object-oriented, so everything is stored in an object  C is more on procedural  There are no classes in C, but there are structs  C++ is a mix of both object-oriented and procedural programming  What you can do in C, you can also do in C++ (in most cases)

Differences Between C/C++ and Java  Why is Java taught first here?  Debate over Java vs C/C++ (Java won)  C/C++ needs to be taught still because it is better in some cases than Java  Implementation wise, packages in java are more functional than libraries in C/C++  C/C++ needs external libraries (OpenGL, OpenCV)  Java is “younger” and more standardized than C/C++  Packages

First C Program (Since we will use this in class) #include int main(void) { printf("Hello, world!\n"); return 0; } // Save this program as hello.c

First C Program (Since we will use this in class)  Then, compile the program with: gcc –o hello hello.cpp  And run it as:./hello  The./ is required in Linux  In Windows, it’s okay to ignore this already

Exercise  Try printing out command line arguments int main(int argc, char* argv[]) { int I; for(i = 0; i < argc; i++) { printf("arg %s\n",argv[i]); } return 0; // non-zero means an error }

Exercise  Try adding this line after printf: printf("%c\n", argv[i][0]); printf("%s\n", argv[i]+1);  What happens?

More on POINTERS  Any variable type can be a pointer type  Java declares everything as a pointer int a; int *b; //int pointer b = &a; // & (used for accessing memory address of variable) a = 5; printf(“%d\n”,*a); //what happens?

Functions  Same as creating methods in Java, but needs to have been declared first before being used void fxn(){ printf(“I am at fxn\n”); } Int main(){ fxn(); return 0; }

Functions  C/C++ has this feature called prototyping (allows functions to be declared before being used) void fxn(); int main() { fxn(); return 0; } void fxn() { printf(“I am fxn\n”); }

Functions: Exercise  What is the difference between these two swap methods? void swap(int a, int b){ int temp; temp = a; a = b; b = temp; } void swap (int *a, int *b) { int temp; temp = *a; *a = *b; *b = temp; }

Inputting in Console printf () – to print out in console scanf () – to input in console int main(){ char aChar; printf("\nEnter a character:"); scanf("%c", &aChar); printf(“Character is %c”, aChar); }

Array assignment with malloc() and free()  Normal array assignment int i[20]; //create an array of int with 20 elements  Heap array assignment int a[] = malloc(sizeof(int) * 20); //create a heap  Difference: dynamic vs static memory (because or realloc() )  Deallocate memory (needed after memory is used. Otherwise, there will be a MEMORY LEAK) free(a);

LAB 2: Sorting algorithm  Write a program sort.c which sorts a list of names  I should be able to run this command:./sort  The first line consists of the number of elements in the list  Then the program should be able to print out the sorted list  The entire thing should be able to sort the names by first name. (to make things simpler) Example input: 4 Jack Frost Jake Long Jane Doe Johnny Appleseed  Make sure that each line should be read as well

LAB 2: Sorting algorithm  Sample first lines: int N; //number of elements in list char *name[]; //string = char * in C char ipline[128]; //read each line scanf("%d\n", &N); name = (char **)malloc(sizeof(char *) * N); for(j = 0; j < N; ++j) { gets(ipline); name[j] = (char *) malloc(strlen(ipline)+1); strcpy(name[j], ipline); } //sort //printout sorted array //free

LAB 2: Sorting algorithm  Of course, I will have to check if you have a CERTIFICATE OF AUTHORSHIP (failure to do so will null and void your lab)  File name: CS162B_Lab2_ _ _.tar  Submit on the link provided for your section. Failure to do so will incur a -10  Deadline: 11:55pm

Next Meeting  More on C  Reading files  Using file pointers  Other features of C

THE END “Faith is taking the first step even if you do not see the whole staircase”