C programming Language – Code snippets

C Programming Language, 2nd Edition

Compiling and running the sample codes using gcc :

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gcc sample.c -o sample
./sample

Chapter 1 – Introductory tutorial : Input/output, characters, strings

0. Hello World!

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#include<stdio.h>
 
int main()
 
{
 
  printf("Hello World\n");
  return 0;
}

1. Word counter

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/* word counter */
#include<stdio.h>
 
#define  IN 1  //inside a word
#define  OUT   0  //outside a word
 
int main()
 
{
  int c,nl,nw,nc,state;
  state=OUT;
  nl=nw=nc=0;
 
  while((c=getchar())!=EOF)
   {
      ++nc;
      if(c=='\n') ++nl;
      if (c==' ' || c == '\n' || c=='\t') state=OUT;
      else if (state==OUT)
         {
           state=IN;
           ++nw;
          }
        }
      printf("lines=%d words=%d characters=%d\n",nl,nw,nc);
 return 0;
}

2. Convert Fahrenheit to Celsius

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#include<stdio.h>
 
#define  LOWER 0
#define  UPPER 300
#define  STEP  20
 
int main()
 
  {
     int fahr;
     for (fahr = LOWER; fahr <= UPPER; fahr=fahr + STEP)
         printf("%3d %6.1f\n", fahr, (5.0/9.0)*(fahr-32));
     return 0;
 }

3. Count characters

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/* character counter */
#include<stdio.h>
 
int main()
 
{
   short int nc;
   for(nc=0; getchar()!=EOF ; ++nc);
   printf("%d\n",nc);
   return 0;
}

4. Count characters by type – digits, white spaces etc.

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/* count digits, white space, others */
#include<stdio.h>
 
int main()
 {
   int c,i,nwhite,nother;
   int ndigit[10];
 
   nwhite=nother=0;
   for(i=0; i < 10; ++i)  ndigit[i]=0;
 
   while((c=getchar())!=EOF)
     if(c>='0' && c<='9') ++ndigit[c-'0'];
     else if (c==' ' || c=='\n' || c=='\t') ++nwhite;
     else  ++nother;
 
   printf("digits=");
   for(i=0;i<10;++i) printf(" %d",ndigit[i]);
   printf(",white space=%d, other=%d\n",nwhite,nother);
 
return 0;
}

5. Copy input to output terminal

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/* copy input to output 1 */
#include<stdio.h>
 
int main()
 
{
   int c;
   c = getchar();
   while ( c!=EOF)
     {
       putchar(c);
       c = getchar();
     }
 return 0;
}

6. Copy input to output terminal (shorter version)

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/* copy input to output */
#include<stdio.h>
 
int main()
{
   int c;
   while((c=getchar())!=EOF)
     putchar(c);
   return 0;
}

7. Print longest line

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#include<stdio.h>
 
#define  MAXLINE  1000  /* maximum input line length */
 
int getline(char line[], int maxline);
void copy(char to[], char from[]);
 
/* print the longest input line */
 
int main()
 
{
  int len;  /* current line length */
  int max;  /* maximum length seen so far */
  char line[MAXLINE];   /* current input line */
  char longest[MAXLINE];   /*longest line saved here */
 
  max=0;
  while((len=getline(line,MAXLINE))>0)
    if(len>max)
       { max=len;
         copy(longest,line);
       }
 if(max>0)  /*there was a line*/
  printf("Longest Line from input is:\n%s\n",longest);
  printf("Line length is: %d characters\n",max);
 
return 0;
}
 
 
/*getline: read a line into s, return length */
 
int getline(char s[], int lim)
{
  int c,i;
  for(i=0; i<lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
   s[i]=c;
 if(c=='\n') {
  s[i]=c;
  ++i;
  }
 s[i]='\0';
 return i;
}
 
/*copy: copy 'from' into 'to'; assume 'to' is big enough */
 
void copy(char to[], char from[])
{
  int i;
  i=0;
  while((to[i]=from[i]) != '\0')
    ++i;
}

8. Print longest line – improved

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#include<stdio.h>
 
#define  MAXLINE  1000  /* maximum input line length */
 
int max;
char line[MAXLINE];
char longest[MAXLINE];
 
int getline(char line[], int maxline);
void copy(char to[], char from[]);
 
/* print the longest input line */
 
int main()
 
{
  int len;  /* current line length */
  extern int max; /* maximum length seen so far */
  extern char longest[MAXLINE];  /*longest line saved here */
 
  max=0;
  while((len=getline(line,MAXLINE))>0)
    if(len>max)
       { max=len;
         copy(longest,line);
       }
 if(max>0)  /*there was a line*/
  printf("Longest Line from input is:\n%s\n",longest);
  printf("Line length is: %d characters\n",max);
 
return 0;
}
 
 
/*getline: read a line into s, return length */
 
int getline(char s[], int lim)
{
  int c,i;
  extern char line[];
  for(i=0; i<lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
   s[i]=c;
 if(c=='\n') {
  s[i]=c;
  ++i;
  }
 s[i]='\0';
 return i;
}
 
/*copy: copy 'from' into 'to'; assume 'to' is big enough */
 
void copy(char to[], char from[])
{
  int i;
  extern char line[], longest[];
  i=0;
  while((to[i]=from[i]) != '\0')
    ++i;
}

9. Power function

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#include<stdio.h>
 
int power(int m, int n);
 
/* test power function */
 
int main()
 
{
  int i;
  for(i=0; i<10; ++i)
   printf("%d %d %d\n",i,power(2,i),power(-3,i));
 return 0;
}
 
int power(int base, int n)
 {
   int i,p=1;
   for(i=1;i<=n;++i)
     p*=base;
   return p;
 }

10. Reverse string

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#include<stdio.h>
 
#define  MAXLINE  1000
 
int size=0;
void reverse(char line[], int lim);
int main()
 
{ extern int size;
  char line[MAXLINE];
  reverse(line,MAXLINE);
  while(size) putchar(line[--size]);
  printf("\n");
  return 0;
}
 
void reverse(char line[], int lim)
 
{
 extern int size;
 int c;
 while((c=getchar())!=EOF ) line[size++]=c;
 line[size]='\0';
 
}

11. Get digits only

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#include<stdio.h>
 
int atoi(char s[]);
 
int main()
 
{
  char str[]="12a4c5 ";
  int i=0,n=0;
 
 while(str[i]!='\0')
   {
      if(str[i]>='0' && str[i]<='9') { n=10*n+(str[i]-'0'); i++; }
      else
       { i++; continue; }
   }
 printf("number=%d\n",n);
 return 0;
 
 }

12. Fahrenheit to Celsius table

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/* print Fahrenheit-Celsius table for fahr =0,20,40,....,300 */
 
#include<stdio.h>
 
int main()
 
{
  int fahr, celsius;
  int lower, upper, step;
  lower = 0;
  upper = 300;
  step = 20;
 
  fahr = lower;
  while( fahr <= upper)
   {
      celsius = 5 * (fahr - 32) / 9;
      printf("%d\t%d\n", fahr, celsius);
      fahr = fahr + step;
   }
 
return 0;
}

Reference –

https://www.amazon.com/Programming-Language-2nd-Brian-Kernighan/dp/0131103628#reader_0131103628