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 2 – Types, Operators and Expressions

1.Convert to lower case.

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#include<stdio.h>
 
int main(int argc, char *argv[])
 
{
 
  while(*argv[1])
   {
     if(*argv[1] >='A' && *argv[1] <='Z') { putchar(*argv[1] + 'a' -'A'); *++argv[1]; }
     else
      {putchar(*argv[1]); *++argv[1]; }
   }
 
printf("\n");
return 0;
}

2. Get bits

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#include<stdio.h>
 
unsigned getbits(unsigned x,int p, int n);
 
int main()
 
{
   int x=16;
   printf("%d\n",getbits(x,4,3));
 
return 0;
}
 
unsigned getbits(unsigned x, int p, int n)
 {
   return ( x >> (p+1-n)) & ~(~0 << n);
 }

3. Count one bits

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#include<stdio.h>
 
int bitcount(unsigned x);
int main()
 
{
  unsigned short x=38;
 
  printf("%d has %d 1 bits\n",x,bitcount(x));
  return 0;
}
 
int bitcount(unsigned x)
 {
   int b;
   for(b=0; x!=0; x>>=1)
    if (x&1) b++;
  return b;
}

4. Remove character from string

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#include<stdio.h>
 
int main(int argc, char *argv[])
 
{
 
 
if (argc !=3)  { printf("usage: del string char\n"); return -1;}
 
while(*argv[1])
 
{
   if(*argv[1] != *argv[2]) { putchar(*argv[1]); *++argv[1]; }
   else
   { *++argv[1]; continue; }
}
printf("\n");
return 0;
 
}

5. Convert x to binary

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#include<stdio.h>
#define  LEN 16
int main()
 
{
  int x=112,counter=0;
  int binary[LEN]={0};
  while(x)
   {
     binary[counter]=x%2; x/=2; counter++;
   }
while(counter>=0) { printf("%d",binary[counter]); counter--; }
printf("\n");
return 0;
}

6. Convert char to integer

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#include<stdio.h>
 
#define NUM 1
 
int main(int argc, char *argv[])
 
{
 int counter=1,n=0;
 
 if(argc!=2) { printf("usage: atoi arglist\n"); return -1;}
 
 while(*argv[NUM])
   {
      if(*argv[NUM]>='0' && *argv[NUM]<='9') { n=10*n+(*argv[NUM]-'0'); *++argv[NUM]; }
      else
       { *++argv[NUM]; continue; }
   }
 printf("number=%d\n",n);
 return 0;
 
 }

Reference –

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