C Cheat Sheet: Quick and Dirty Guide, Cheat Sheet of C programming

Download C Cheat Sheet: Quick and Dirty Guide and more Cheat Sheet C programming in PDF only on Docsity! Quick and Dirty Guide to C The single best book on C is The C Programming Language by Kernighan and Richie. CODE: Code for execution goes into files with “.c” suffix. Shared decl’s (included using #include “mylib.h”) in “header” files, end in “.h” COMMENTS: Characters to the right of // are not interpreted; they’re a comment. Text between /* and */ (possibly across lines) is commented out. DATA TYPES: Name! ! Size! Description char! ! 1 byte! an ASCII value: e.g. ‘a’ (see: man ascii) int/long! 4 bytes !a signed integer: e.g. 97 or hex 0x61, oct 0x141 long long ! 8 bytes! a longer multi-byte signed integer float! ! 4 bytes! a floating-point (possibly fractional) value double!! 8 bytes !a double length float char, int, and double are most frequently and easily used in small programs sizeof(double) computes the size of a double in addressable units (bytes) Zero values represent logical false, nonzero values are logical true. Math library (#include <math.h>, compile with -lm) prefers double. CASTING: Preceding a primitive expression with an alternate parenthesized type converts or “casts” value to a new value equivalent in new type: int a - (int) 3.131; ! //assigns a=3 without complaint Preceding any other expression with a cast forces new type for unchanged value. double b = 3.131; int a = *(int*)&b; //interprets the double b as an integer (not necessarily 3) STRUCTS and ARRAYS and POINTERS and ADDRESS COMPUTATION: Structs collect several fields into a single logical type: struct { int n; double root;} s; //s has two fields, n and root s.root = sqrt((s.n=7)); //ref fields (N.B. double parens=>assign OK!) Arrays indicated by right associative brackets ([]) in the type declaration int a[10]; //a is a 10int array. a[0] is the first element. a[9] is the last char b[]; //in a function header, b is an array of chars with unknown length int c[2][3]; //c is an array of 2 arrays of three ints. a[1][0] follows a[0][2] Array variables (e.g. a,b,c above) cannot be made to point to other arrays Strings are represented as character arrays terminated by ASCII zero. Pointers are indicated by left associative asterisk (*) in the type declarations: int a*a; // a is a pointer to an integer char *b; // b is a pointer to a character int *c[2]; // c is an array of two pointers to ints (same as int *(c[2]); int (*d)[2]; // d is a pointer to an array of 2 integers Pointers are simply addresses. Pointer variables may be assigned. Adding 1 computes pointer to the next value by adding sizeof(X) for type X General int adds to pointer (even 0 or negative values) behave in the same way Addresses may be computed with the ampersand (&) operator. An array without an index or a struct without field computes its address: int a[10], b[20]; // two arrays int *p = a; // p points to first int of array a p = b; // p now points to the first int of array b An array or pointer with an index n in square brackets returns the nth value: int a[10]; // an array int *p; int i = a[0]; // i is the first element of a i = *a; // pointer dereference p = a; // same as p = &a[0] p++; // same as p = p+1; same as p=&a[1]; same as p = a+1 Bounds are not checked; your responsibility not to run off. Don’t assume. An arrow (-> no spaces!) dereferences a pointer to a field: struct { int n; double root; } s[1]; //s is pointer to struct or array of 1 s->root = sqrt)s->n = 7); //s->root same as (*s).root or s[0].root printf(“%g\n”, s->root); FUNCTIONS: A function is a pointer to some code, parameterized by formal parameters, that may be executed by providing actual parameters. Functions must be declared before they are used, but code may be provided later. A sqrt function for positive n might be declared as: double sqrt(double n) { double guess; for (guess = n/2.0; abs(n-guess*guess)>0.001; guess = (n/guess+guess)/2); return guess; } This function has type double (s*sqrt)(double). printf(“%g\n”, sqrt(7.0)); //calls sqrt; actuals are always passed by value Functions parameters are always passed by value. Functions must return a value. The return value need not be used. Function names with parameters returns the function pointer. Thus, an alias for sqrt may be declared: double (*root)(double) = sqrt; printf(“%g\n”, root(7.0)); Procedures or valueless functions return ‘void’. There must always be a main function that returns an int. int main(int argc, char **argv) OR int main(int argc, char *argv[]) Program arguments may be accessed as strings through main’s array argv with argc elements. First is the program name. Function declarations are never nested. OPERATIONS: +, -, *, /, %! Arithmetic ops. /truncates on integers, % is remainder. ++i --i!! Add or subtract 1 from i, assign result to i, return new val i++ i--!! Remember i, inc or decrement i, return remembered value && || !!! Logical ops. Right side of && and || unless necessary & | ^ ~!! Bit logical ops: and, or, xor, complement. >> <<! ! Shift right and left: int n=10; n <<2 computes 40. = ! ! Assignment is an operator. Result is value assigned. += -= *= etc ! Perform binary op on left and right, assign result to left == != < > <= >= Comparison operators (useful only on primitive types) ?:! ! If-like expression: (x%2==0)?”even”:”odd” ,! ! computing value is last: a, = b,c,d; exec’s b,c,d then a=d STATEMENTS: Angle brackets identify syntactic elements and don’t appear in real statements <expression> ;!! //semicolon indicates end of a simple statement break;!! ! //quits the tightest loop or switch immediately continue;! ! //jumps to next loop test, skipping rest of loop body return x;! ! //quits this function, returns x as value { <statements> } ! //curly-brace groups statements into 1 compound (no ;) if (<condition>) <stmt>!//stmt executed if cond true (nonzero) if (<condition>) <stmt> else <stmt> // two-way condition while (<condition>) <stmt> //repeatedly execute stmt only if condition true do <stmt> while (<condition>); //note the semicolon, executes at least once for (<init>; <condition>; <step>) <statement> switch (<expression>) { ! //traditional “case statement” case <value>: <statement>! // this statement exec’d if val==expr ! ! break;! ! // quit this when value == expression case <value2>: <statement2>! //executed if value2 = expression case <value3>: <statement3> //executed if value3 = expression ! ! break;! ! // quit default: <statement4>!! // if matches no other value; may be first ! ! break;! ! // optional (but encouraged) quit } KEY WORDS unsigned! before primitive type suggests unsigned operations extern!! in global declaration => symbol is for external use static!! in global declaration => symbol is local to this file ! ! in local decl’n => don’t place on stack; keep value betw’n calls typedef! before declaration defines a new type name, not a new variable