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Tom Kelliher, CS 320

Jan. 26, 2011

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Assignment

Read 1.1-4.

Outline

1. Syllabus.

2. Terminal I/O in C.

3. Accessing command-line arguments.

Coming Up

Structures, pointers, and memory allocation in C

Syllabus

Terminal I/O in C

1. printf

   #include <stdio.h>
   
   int main()
   {
      /* Variable declarations must occur at the _start_ of a block. */
      int sum = 12;
      double min = 0.1, max = 5.5;
      char name[] = "Tom Kelliher";
   
      printf("I am a constant string.\n");
   
      printf("The sum is: %d\n", sum);
   
      printf("Min is: %g.  Max is: %g.\n", min, max);
   
      printf("Your name is %s.\n", name);
   
      return 0;
   }
   

   Refer to printf(3C) on phoenix. (man -s 3C printf)

2. scanf

   #include <stdio.h>
   
   int main()
   {
      int i, age;
      double weight;
      char name[80];
   
      printf("Enter your age: ");
      scanf("%d", &age);
      printf("You entered %d.\n", age);
   
      printf("Enter sample weight: ");
      scanf("%lg", &weight);
      printf("You entered %g.\n", weight);
   
      printf("Enter your name: ");
      scanf("%s", name);
      printf("Your name is %s.\n", name);
   
      /* Eliminate whitespace following previous name. */
      while (getc(stdin) != '\n')
         ;
   
      printf("Enter your name: ");
      fgets(name, 80, stdin);
   
      /* Eliminate the newline following name */
      i = 0;
      while (name[i] != '\n')
         i++;
   
      name[i] = '\0';
   
      printf("Your name is %s.\n", name);
   
      return 0;
   }
   

   Refer to scanf(3C).

Command-Line Arguments

1. Command-line arguments in Unix:

   foo arg1 arg2 arg3
   

2. Command-line arguments in Eclipse:

3. Command-line arguments in Eclipse: Open the Run Dialog for your build command, select the Arguments tab, and enter the arguments. Each argument should be separated by a space.

4. Example:

   #include <stdio.h>
   #include <stdlib.h>
   
   int main(int argc, char *argv[])
   {
      int sum, current, i;
   
      if (argc <= 1)
      {
         printf("No arguments!\n");
         return 1;
      }
   
      sum = 0;
      for (i = 1; i < argc; i++)
      {
         current = atoi(argv[i]);
         sum += current;
         printf("Arg %d: %d\n",  i, current);
      }
   
      printf("\nThe sum is %d.\n", sum);
   
      return 0;
   }
   

5. Another example, showing highly desirable output buffering disabling:

   #include <stdio.h>
   
   int main(int argc, char *argv[])
   {
     int i;
     
     setvbuf(stdout, (char *)NULL, _IONBF, 0);
     setvbuf(stderr, (char *)NULL, _IONBF, 0);
     
     printf(``Command: %s\n'', argv[0]);
     
     for (i = 1; i < argc; i++)
     printf(``Arg: %s\n'', argv[i]);
     
     return 0;
   }
   

Practice

1. Creating a console program in Eclipse:
   1. Open the File, New, C Project.

   2. Give the project a name and ensure that MinGW GCC is used for the toolchain.

      Project type should be Executable.

2. Creating new source files: File, New.

3. Usually, you want to create a source file, so choose Source file. When you name the file, it should have an extension of .c.

   Sometimes, you want a header file. At those times, choose Header File. The filename should have an extension of .h.

4. To run your program, open the Run As drop-down, select Open Run Dialog, then create a new C/C++ Local Application.

5. Practice program: Write a C program which accepts exactly three integer command-line arguments and prints the largest of them.

6. Another practice program using malloc(): Write a C program which takes a single integer as a command-line argument, creates an int array with that many elements, reads that many inputs from stdin, and the outputs the inputs in reverse order.

Tom Kelliher