C programming Language – Code snippets
C Programming Language, 2nd Edition
Compiling and running the sample codes using gcc :
gcc sample.c -o sample
./sample
Chapter 3 – Control Flow
1. Trim whitespace
#include<stdio.h>
#include<string.h>
int main()
{
int n,i=0;
char s[]=" HELLO THERE ";
printf("Before trim:%s\n",s);
for(n=strlen(s)-1; n>=0; n--)
if(s[n]!=' ' && s[n]!='\t' && s[n]!='\n') break;
s[n+1]='\0';
while(isspace(s[i++]));
i=0;
while(s[i]!='\0') s[i++];
s[i]='\0';
printf("After trim:%s\n",s);
return n;
}
2. Binary search
#include<stdio.h>
int binsearch(int x, int v[], int n);
int main(int argc, char *argv[])
{
int size=argc,found;
int counter=0,x, v[size-2];
x=atoi(argv[size-1]);
if (argc<3) {printf("Usage: progname integer-list integer-to-be-searched\n"); return -1; }
while(counter <= size-3)
{ v[counter]=atoi(argv[counter+1]);
counter++; }
(found=binsearch(x,v,size-2))!=-1 ? printf("Found=%d\n",v[found]): printf("Not found\n");
return 0;
}
int binsearch(int x, int v[], int n)
{
int low, high, mid;
low=0;
high=n-1;
while(low<=high)
{
mid=(low+high)/2;
if(x < v[mid]) high=mid-1;
else if (x > v[mid]) low=mid+1;
else
return mid;
}
return -1;
}
3. Integer to string with argument parsing.
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define SIZE 10
void itoa(int n, char s[]);
void reverse(char s[]);
int main(int argc, char *argv[])
{
char s[SIZE];
int n;
if(argc!=2) { printf("Usage: progrname integer\n"); return -1; }
n=atoi(argv[1]);
itoa(n,s);
printf("String:%s\n",s);
return 0;
}
void itoa(int n, char s[])
{
int i, sign;
if((sign=n)<0) n=-n;
i=0;
do {
s[i++]=n%10 + '0';
} while( (n/=10)>0);
if (sign<0) s[i++]='-';
s[i]='\0';
reverse(s);
}
void reverse(char s[])
{
int c, i, j;
for(i=0,j=strlen(s)-1; i<j; i++,j--)
{
c=s[i]; s[i]=s[j]; s[j]=c;
}
}
4. Reverse string and convert integer to string
#include<stdio.h>
#include<string.h>
#define SIZE 1000
void reverse(char s[]);
void itoa(int n, char s[]);
int main()
{
char s[SIZE]="HELLO WORLD!!";
reverse(s);
printf("%s\n",s);
itoa(87690,s);
printf("%s\n",s);
return 0;
}
void reverse(char s[])
{
int c, i, j;
for(i=0,j=strlen(s)-1; i<j; i++,j--)
{
c=s[i]; s[i]=s[j]; s[j]=c;
}
}
void itoa(int n, char s[])
{
int i, sign;
if((sign=n)<0) n=-n;
i=0;
do {
s[i++] = n%10 + '0';
} while((n/=10)>0);
if(sign<0) s[i++] = '-';
s[i]='\0';
reverse(s);
}
5. Command line argument parsing
#include<stdio.h>
int main(int argc, char *argv[])
{
int i,counter;
printf("Number of arguments:%d\n",argc);
printf("Arguments character-by-character\n");
for(counter=0;counter < argc ; counter++)
{ while(*argv[counter])
printf("%c ",*argv[counter]++);
printf("\n");
}
printf("\n");
return 0;
}
6. Reverse a string
#include<stdio.h>
#include<string.h>
#define SIZE 1000
void reverse(char s[]);
int main()
{
char s[SIZE]="HELLO WORLD!";
reverse(s);
printf("%s\n",s);
return 0;
}
void reverse(char s[])
{
int c, i, j;
for(i=0,j=strlen(s)-1; i<j; i++,j--)
{
c=s[i]; s[i]=s[j]; s[j]=c;
}
}
7. Sorting with shell sort method.
#include<stdio.h>
#define SIZE 10
void shellsort(int v[], int n);
int main()
{
int counter;
int v[SIZE]={8,13,9,45,90,24,56,11,20,10};
shellsort(v,SIZE);
for(counter=0; counter<SIZE; counter++)
printf("%d ",v[counter]);
printf("\n");
return 0;
}
void shellsort(int v[], int n)
{
int gap, i, j, temp;
for(gap=n/2; gap>0; gap/=2)
for(i=gap; i<n; i++)
for(j=i-gap; j>=0 && v[j]>v[j+gap]; j-=gap)
{
temp=v[j];
v[j]=v[j+gap];
v[j+gap]=temp;
}
}
8. using switch case
#include<stdio.h>
int main()
{
int c, i, nwhite, nother,alpha, ndigit[10];
nwhite=nother=alpha=0;
for(i=0; i<10; i++) ndigit[i]=0;
while((c=getchar())!=EOF)
{
switch(c)
{
case '0': case '1': case '2': case '3': case '4': case '5':
case '6': case '7': case '8': case '9':
ndigit[c-'0']++; break;
case ' ': case '\n': case '\t': nwhite++; break;
default:
nother++; break;
}
}
printf("Digits =");
for(i=0; i<10; i++) printf(" %d", ndigit[i]);
printf(", white space =%d, other = %d\n", nwhite, nother);
return 0;
}
9. Double input – strip out non integers
#include<stdio.h>
#include<ctype.h>
#define SIZE 10
int atoi(char s[]);
int main(int argc, char *argv[])
{
int counter=0;
char s[SIZE];
if (argc!=2) {
printf("Usage: progname integer\n");
return 1;
}
while(*argv[1]) s[counter++]=(*argv[1]++);
printf("Twice Result=%d\n",2*atoi(s));
return 0;
}
int atoi(char s[])
{
int n, i,sign;
for(i=0; isspace(s[i]); i++);
sign=(s[i]=='-')? -1: 1;
if(s[i] == '+' || s[i] == '-') i++;
for(n=0; isdigit(s[i]); i++)
n=10*n + (s[i]-'0');
return sign*n;
}
Reference –
https://www.amazon.com/Programming-Language-2nd-Brian-Kernighan/dp/0131103628#reader_0131103628
