1.1 The Basics of C Environment

 
 
 

1.2 Program Output

 
 

#include <stdio.h>  int main(void)  {     printf("from sea to shining C\n");     return 0;  }

 

#include <stdio.h>  int main(void)  {     printf("from sea to ");     printf("shining C");     printf("\n");     return 0;  }

 

#include <stdio.h>  int main(void)  {     printf("from sea\n");     printf("to shining\nC\n");     return 0;  }

 

#include <stdio.h>  int main(void)  {     printf("\n\n\n\n\n");     printf("                    ************************\n");     printf("                    *      from sea                        *\n");     printf("                    *      to shining C                   *\n");     printf("                    ************************\n");     printf("\n\n\n\n\n");     return 0;  }

 

1.3 Variables, Expressions, Assignment

 

/* The distance of a marathon in kilometers. */  #include <stdio.h>  int main(void)  {     int miles, yards;     float kilometers;     miles = 26;     yards = 385;     kilometers = 1.609 * (miles + yards / 1760.0);     printf("\nA marathon is %f kilometers.\n\n", kilometers);     return 0;  }

 

1.4 The Use of #define and #include

 

#define  LIMIT  100  #define  PI  3.14159  #defince   C  299792.458   /*speed of light in km/sec  */  printf("PI = %f\n", PI);

 

#include  "my_file.h"  #include <stdio.h>

 

In file pacific_sea.h:  #include <stdio.h>  #define  AREA            2337  #define  SQ_MILES_PER_SQ_KILOMETER  0.386102158  #define  SQ_FEET_PER_SQ_MILE                 (5280*5280)  #define  SQ_INCHES_PER_SQ_FOOT            144  #define  ACRES_PER_SQ_MILE                     640

 

In file pacific_sea.c:  /*Measuring the Pacific Sea*/  #include "pacific_sea.h"  int main(void)  {   const int pacif_sea = AREA;   /* in sq kilometers */   double  acres, sq_miles, sq_feet, sq_inches;   printf("\nThe Pacific Sea covers an area");   printf(" of %d square kilometers.\n", pacific_sea);   sq_miles=SQ_MILES_PER_SQ_KILOMETER*pacific_sea;   sq_feet=SQ_FEET_PER_SQ_MILES*sq_miles;   sq_inches=SQ_INCHES_PER_SQ_FOOT*sq_feet;   acres=ACRES_PER_SQ_MILE*sq_miles;   printf("In other units of measure this is:\n\n");   printf("%22.7e acres\n", acres);   printf("%22.7e square miles\n", sq_miles);   printf("%22.7e square feet\n", sq_feet);   printf("%22.7e square inches\n\n", sq_inches);   return 0;  }

 

1.5 The Use of printf() and scanf()

 

printf("abc");  printf("%s", "abc");  printf("%c%c%c", 'a', 'b', 'c');

 

printf()  ==>  %c            as a character  %d            as a decimal integer  %e            as a floating point number in scientific notation  %f            as a floating point number  %g            in the e-format or f-format, whichever is shorter  %s            as a string

 

printf("%c%3c%5c\n",  'A', 'B', 'C');

 

scanf("%d", &x);    ==>   address

 

scanf()     ===>  %c            to a character  %d            to a decimal integer  %f             to a floating point number (float)  %lf            to a floating point number (double)  %LF          to a floating point number (long double)  %s             to a string

 

#include <stdio.h>  int main(void)  {   char c1, c2, c3;   int i;   float x;   double y;   printf("\n%s\n%s",        "Input three characters,"        "an int, a float, and a double: ");   scanf("%c%c%c%d%f%lf", &c1, &c2, &c3, &i, &x, &y);   printf("\nHere is the data that you typed in:\n");   printf("%3c%3c%3c%5d%17e%17e\n", c1, c2, c3,i,x,y);   return 0;  }

 

1.6 Flow of Control

 

if (expr)                     statement

 

a = 1;  if (b == 3)        a = 5;  printf("%d", a);

 

Compund statement:  if (a == 3) {     b = 5;     c = 7;  }

 

if (expr)                   statement1             else                   statement2

 

if (cnt == 0) {     a = 2;     b = 3;     c = 5;  }  else {     a = -1;     b = -2;     c = -3;  }  printf("%d", a+b+c);

 
while

#include <stdio.h>  int main(void)  {    int  i = 1, sum = 0;    while (i <= 5) {       sum += i;       ++i;    }    printf("sum = %d\n", sum);    return 0;  }

 

for (expr1; expr2; expr3)                    statement;  is equivalent to:           expr1;           while (expr2) {                   statement;                   expr3;           }

 

for (i = 1; i <= 5;  ++i)        sum += i;

 

/* Compute the minimum, maximum, sum, and average */ #include <stdio.h> #include <stdlib.h> int main(void) {  int  i;  double x, min, max, sum, avg;  if(scanf("%lf", &x)!=1) {     printf("No data found - bye!\n");     exit(1);  }  min = max = sum = avg = x;  printf("%5s%9s%9s%9s%12s%12s\n%5s%9s%9s%9s%12s%12s\n\n",      "Count", "Item", "Min", "Max", "Sum", "Average",      "-----", "-----", "---", "---", "---", "-------");  printf("%5d%9.1f%9.1f%9.1f%12.3f%12.3f\n",      1, x, min, max, sum, avg);  for(i =2; scanf("%lf", &x) == 1; ++i) {     if( x < min)        min = x;     else if (x > max)        max = x;     sum += x;     avg = sum / i;     printf("%5d%9.1f%9.1f%9.1f%12.3f%12.3f\n",        i, x, min, max, sum, avg);  }  return 0; }

 

1.7 Functions

 

function declaration: double pow(double x, double y); function prototype: double pow(double, double);

 

#include < stdio.h> float maximum(float x, float y); float minimum(float x, float y); void prn_info(void); int main(void) {  int i, n;  float max, min, x;  prn_info();  printf("Input n: ");  scanf("%d", &n);  printf("\nInput %d real numbers: ",n);  scanf("%f", &x);  max = min = x;  for(i =2; i<=n; ++i) {     scanf("%f", &x);     max = maximum(max, x);     min = minimum(min, x);  }  printf("\n%s%11.3f\n%s%11.3f\n\n",     "Maximum value:", max,     "Minimum value:", min);  return 0; } float maximum(float x, float y) {  if (x > y)     return x;  else     return y; } float minimum(float x, float y) {  if(x < y)     return x;  else     return y; } void prn_info(void) {  printf("\n%s\n%s\n\n",    "This program reads an integer value for n, and then",    "processes n real numbers to find max and min values."); }

 

CALL BY VALUE   #include < stdio.h>    void try_to_change_it(int); int main(void) {  int a = 1;  printf("%d\n", a);   /* 1 is printed*/  try_to_change_it(a);  printf("%d\n", a);   /* 1 is printed again! */  return 0; } void try_to_change_it(int a) {     a = 777; }

 

1.8 Arrays, Strings, and Pointers

 

Arrays: int a[3];

 

#include <stdio.h> #define CLASS_SIZE 5 int main(void) {  int i, j, score[CLASS_SIZE], sum = 0, tmp;  printf("Input %d scores: ", CLASS_SIZE);  for(i = 0; i < CLASS_SIZE; ++i) {     scanf("%d", &score[i]);     sum += score[i];  }  for(i = 0; i < CLASS_SIZE - 1; ++i)  /*bubble sort*/     for(j = CLASS_SIZE - 1; j > i; --j)        if (socre[j-1] < score[j]) {  /*check the order*/           tmp = score[j-1];           score[j-1] = score[j];           score[j] = tmp;        }  printf("\nOrdered scores:\n\n");  for(i = 0; i < CLASS_SIZE; ++i)     printf("   score[%d]=%5d\n", i, score[i]);  printf("\n%18d%s\n%18.1f%s\n\n",     sum, " is the sum of all the scores",     (double)sum/CLASS_SIZE, " is the class average");  return 0; }

 

STRINGS: /*Have a nice day! */ #include <ctype.h> #include <stdio.h> #define MAXSTRING  100 int main(void) {  char c, name[MAXSTRING];  int i, sum = 0;  printf("\nHi! What is your name? ");  for(i=0; (c=getchar()) != '\n'; ++i) {     name[i] = c;     if(isalpha(c))        sum += c;  }  name[i] = '\0';  printf("\n%s%s%s\n%s",     "Nice to meet you ", name, ".",     "Your name spelled backwards is ");  for(--i; i >=0; --i)     putchar(name[i]);  printf("\n%s%d%s\n\n%s\n",     "and the letters in your name sum to ", sum, ".",     "Have a nice day!");  return 0; }

 

POINTERS: #include <stdio.h> #include <string.h> #define MAXSTRING   100 int main(void) {  char  c = 'a', *p, s[MAXSTRING];  p = &c;  printf("%c%c%c ", *p, *p +1, *p +2);  strcpy(s, "ABC");  printf("%s %c%c%s\n", s, *s + 6, *s +7, s+1);  strcpy(s, "she sells sea shells by the seashore");  p = s+14;  for( ; *p != '\0'; ++p) {     if (*p == 'e')        *p = 'E';     if (*p == ' ')        *p = '\n';  }  printf("%s\n", s);  return 0; }

 

1.9 Files

 

#include <stdio.h> int main(void) {   int c;   FILE  *ifp;   ifp = fopen("my_file", "r");

 

Three modes for a file "r"    for read "w"   for write "a"   for append

 

#include <stdio.h> int main(int argc, char *argv[]) {    .....

 

/*Count uppercase letters in a file. */ #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) {  int c, i, letter[26];  FILE  *ifp, *ofp;  if(argc != 3) {     printf("\n%s%s%s\n\n%s\n%s\n\n",        "Usage:  ", argv[0], "  infile  outfile",        "The uppercase letters in infile will be counted.",        "The results will be written in outfile.");     exit(1);  }  ifp = fopen(argv[1], "r");  ofp = fopen(argv[2], "w");  for(i = 0; i < 26; ++i)  /*initialize array to zero*/     letter[i] = 0;  while ((c = getc(ifp)) != EOF)     if(c>='A' && c<= 'Z')  /*find uppercase letters*/        ++letter[c-'A'];  for(i = 0; i < 26; ++i) {   /*print results*/     if (i %6 == 0)        putc('\n', ofp);     fprintf(ofp, "%c:%5d    ", 'A'+i, letter[i]);  }  putc('\n', ofp);  return ;0; }

 

1.10 Operating System Considerations

 

steps to be followed in writing and running a C program: 1. vi pgm.c 2. cc pgm.c 3. a.out

 

Interrupting a program: ctrl-c

 

Redirection of the input and the output: ls ls > tmp a.out a.out < infile a.out > outfile a.out < infile > outfile