C programming Language – Code snippets 4
Posted by danielMay 28
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 4 – Functions and Program structure
1. A conditional in the C preprocessor
#include<stdio.h> #define SYSTEM 5 #if SYSTEM == 1 #define HDR 10 #elif SYSTEM == 2 #define HDR 20 #elif SYSTEM == 3 #define HDR 30 /*#else #define HDR 0*/ #endif #if !defined(HDR) #define HDR 50 #endif int main() { printf("HDR = %d \n", HDR); return 0; }
2. Macro definitions
#include<stdio.h> #define max(A,B) ((A)>(B) ? (A) : (B)) #define forever for(;;) #define square(x) ((x)*(x)) #define dprint(expr) printf(#expr " = %g\n", expr) #define paste(front, back) front ## back int main() { char name[]="daniel"; int counter=0,x=4,y=2; printf("Max=%d\n",max(8,9)); forever { printf(" %d ", counter); if ( counter++ >= 10) break; } printf("\n"); printf("Square of 4 is %d\n",square(4)); dprint(x/y); return 0; }
3. Pattern matching
#include<stdio.h> #define MAXLINE 1000 int getline(char line[], int max); int strindex(char source[], char searchfor[]); char pattern[]="dan"; int main() { char line[MAXLINE]; int found=0; while(getline(line,MAXLINE)>0) if(strindex(line,pattern) >= 0) { printf("%s",line); found ++; } return found; } int getline(char s[], int lim) { int c, i; i=0; while(--lim > 0 && (c=getchar()) != EOF && c!='\n') s[i++]=c; if(c=='\n') s[i++]=c; s[i]='\0'; return i; } int strindex(char s[], char t[]) { int i,j,k; for(i=0; s[i]!='\0'; i++) { for(j=i, k=0; t[k]!='\0' && s[j]==t[k]; j++, k++); if(k>0 && t[k] == '\0') return i; } return -1; }
4. Reverse polish calculator
/*reverse Polish calculator */ #include<stdio.h> #include<stdlib.h> #include<ctype.h> #define MAXOP 100 #define NUMBER '0' #define MAXVAL 100 #define BUFSIZE 100 int getch(void); void ungetch(int); int getop(char []); void push(double); double pop(void); int sp = 0; double val[MAXVAL]; char buf[BUFSIZE]; int bufp=0; int main() { int type; double op2; char s[MAXOP]; while((type=getop(s)) != EOF) { switch(type) { case NUMBER: push(atof(s)); break; case '+': push(pop() + pop()); break; case '-': op2=pop(); push(pop() - op2); break; case '*': push(pop() * pop()); break; case '/': op2=pop(); if(op2 != 0.0) push(pop()/op2); else printf("Error: zero divisor\n"); break; case '\n': printf("\t%.8g\n", pop()); break; default: printf("Error: unknown command %s\n", s); break; } } return 0; } void push(double f) { if(sp < MAXVAL) val[sp++] = f; else printf("Error: stack full, can't push %g\n", f); } double pop(void) { if(sp > 0) return val[--sp]; else { printf("Error: stack empty\n"); return 0.0; } } int getop(char s[]) { int i, c; while((s[0] = c = getch()) == ' ' || c == '\t') ; s[1] = '\0'; if(!isdigit(c) && c!= '.') return c; i=0; if(isdigit(c)) while(isdigit(s[++i] = c= getch())) ; if ( c=='.') while(isdigit(s[++i] = c = getch())) ; s[i] = '\0'; if ( c!= EOF) ungetch(c); return NUMBER; } int getch(void) { return (bufp > 0) ? buf[--bufp] : getchar(); } void ungetch(int c) { if (bufp >= BUFSIZE) printf("ungetch: too many characters\n"); else buf[bufp++]=c; }
5. Quick sort
#include<stdio.h> void qsort(int v[], int left, int right); int main() { int i, v[]={9,5,8,12,56,7,1,19,27,99,27,13,3}; for(i=0; i<13; i++) printf(" %d ",v[i]); printf("\n"); qsort(v,0,12); for(i=0; i<13; i++) printf(" %d ",v[i]); printf("\n"); return 0; } void qsort(int v[], int left, int right) { int i, last; void swap(int v[], int i, int j); if(left >= right) return; swap(v, left, (left + right)/2); last = left; for(i=left+1; i<=right; i++) if(v[i] < v[left]) swap(v,++last, i); swap(v, left, last); qsort(v, left, last-1); qsort(v, last+1, right); } void swap(int v[], int i, int j) { int temp; temp = v[i]; v[i] = v[j]; v[j] = temp; }
6. Rudimentary calculator
#include<stdio.h> #include<ctype.h> #define MAXLINE 100 double atof(char s[]); int getline(char line[], int max); int main() { double sum, atof(char []); char line[MAXLINE]; int getline(char line[], int max); sum=0; while(getline(line,MAXLINE) > 0) printf("\t%g\n", sum+=atof(line)); return 0; } double atof(char s[]) { double val, power; int i, sign; for (i=0; isspace(s[i]); i++); sign=(s[i]=='-') ? -1: 1; if(s[i]=='+' || s[i] == '-') i++; for (val=0.0; isdigit(s[i]); i++) val = 10.0 * val + (s[i] - '0'); if(s[i] == '.') i++; for(power=1.0; isdigit(s[i]); i++) { val = 10.0*val + (s[i] - '0'); power*=10; } return (sign*val/power); } int getline(char line[], int max) { int c,i; for(i=0; i<max-1 && (c=getchar())!=EOF && c!='\n'; ++i) line[i]=c; if(c=='\n') { line[i]=c; ++i; } line[i]='\0'; return i; }
7. ASCII string to float conversion
#include<stdio.h> #include<ctype.h> int main() { double val, power; int i, sign; char s[]=" -23.590 "; for (i=0; isspace(s[i]); i++); sign=(s[i]=='-') ? -1: 1; if(s[i]=='+' || s[i] == '-') i++; for (val=0.0; isdigit(s[i]); i++) val = 10.0 * val + (s[i] - '0'); if(s[i] == '.') i++; for(power=1.0; isdigit(s[i]); i++) { val = 10.0*val + (s[i] - '0'); power*=10; } printf("Value = %f\n", (sign*val/power)); return 1; }
References –
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