First c program
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The document provides an introduction to the basics of writing a C program. It explains that a C program contains functions, with main() being required. The main() function contains statements that are terminated with semicolons. It also describes common data types in C like int, char, and float, and how to declare variables. The document shows how to use literals, initialize variables, and take user input using scanf.
First c program
- 1. A First C Program
- 2. Try#include <stdio.h> C/*Program */ Your First I/O header file pre-processor directive header file – contains I/O routines main() Indicates a { program building block called function comment main must be present in each C program one statement printf(“Hello world ”); statement terminator printf(“Welcome to CSCI230n“); printf(“I am John Smithn”); } A C program contains one or more functions main() is the function name of your main (root) program { }: braces (left & right) to construct a block containing the statements of a function Every statement must end with a ; is called an escape character n is an example of an escape sequence which indicates newline Other escape sequences are: t r a ” Exercise: Use any editor to type and then save your first program as main.c % gcc main.c % a.out and observe its result.
- 3. Variable identifiers Identifiers Begin with a letter or underscore: A-Z, a-z, _ The rest of the name can be letters, underscore, or digits Guarantee that east least the first 8 characters are significant (those come after the 8th character will be ignored) while most of C compiler allows 32 significant characters. Example: _abc ABC Time time _a1 abcdefgh abcdefghi (may be the same as abcdefgh) Case sensitive Keywords: reserved names (lexical tokens) auto double if static break case entry long typedef float else switch char return union int struct extern register do go sizeof continue …
- 4. Fundamental Data Type Four Data Types (assume 2’s complement, byte machine) Data Type Size (byte) Range char 1 -128 ~ 127 unsigned char char Abbreviation 1 0 ~ 255 2 or 4 -215 ~ 215-1 or -231 ~ 231-1 2 or 4 0 ~ 65535 or 0 ~ 232-1 int unsigned int short int short 2 -32768 ~ 32767 unsigned short int unsigned short 2 0 ~ 65535 long int long 4 -231 ~ 231-1 unsigned long int int unsigned unsigned long 4 0 ~ 232-1 float double Note: 4 8 27 = 128, 215 =32768, 231 = 2147483648 Complex and double complex are not available
- 5. Variable Declarations type v1,v2,v3, …, vn Example: int i; int j; float k; char c; short int x; long int y; unsigned int z; int a1, a2, a3, a4, a5;
- 6. Numeric, Char, String Literals Literal Numeric literal fixed-point octal O32 (= 24D) (covered later) hexadecimal OxFE or Oxfe (=254D) (covered later) decimal int 32 long (explicit) 32L or 32l an ordinary integer literal that is too long to fit in an int is also too long for long floating-point No single precision is used; always use double for literal Example: 1.23 123.456e-7 0.12E
- 7. Numeric, Char, String Literals • Character literal (covered later) • American Standard Code for Information Interchange (ASCII) single space 32 ‘0’ - ‘9’ 48 - 57 ‘A’ - ‘Z’ 65 - 90 ‘a’ - ‘z’ • Printable: 97 - 122 • Nonprintable and special meaning chars „n‟ new line „‟ back slash „0‟ null 9 0 „f‟ formfeed 10 „t‟ tab „‟‟ single quote 39 „b‟ back space 12 8 ‟r‟ carriage return „”‟ double quote 34 „ddd‟ arbitrary bit pattern using 1-3 octal digits „Xdd‟ for Hexadecimal mode „017‟ or „17‟ Shift-Ins, ^O „04‟ or „4‟ or „004‟ „033‟ or „X1B‟ 9 <esc> EOT (^D) 13
- 8. Numeric, Char, String Literals String Literal will be covered in Array section String is a array of chars but ended by „0‟ String literal is allocated in a continuous memory space of Data Segment, so it can not be rewritten A B C D „0‟ ... Example: “ABCD” 4 chars but takes 5 byte spaces in memory Question: “I am a string” takes ? Bytes Ans: 13+1 = 14 bytes
- 9. Numeric,literals & ASCII codes: • Character Char, String Literals char x; x=„a‟; /* x = 97*/ Notes: – „a‟ and “a” are different; why? „a‟ is the literal 97 “a” is an array of character literals, { „a‟, „0‟} or {97, 0} – “a” + “b” +”c” is invalid but „a‟+‟b‟+‟c‟ = ? (hint: „a‟ = 97 in ASCII) „a‟ + „b‟ + „c‟ = 97 + 98 + 99 = 294 = 256 + 38 in the memory 1 38 – if the code used is not ASCII code, one should check out each value of character
- 10. Initialization If a variable is not initialized, the value of variable may be either 0 or garbage depending on the storage class of the variable. int i=5; float x=1.23; char c=„A‟; int i=1, j,k=5; char c1 = „A‟, c2 = 97; float x=1.23, y=0.1;
- 11. Memory Concepts Each variable has a name, address, type, and value 1) int x; 2) scanf(“%d”, &x); 3) user inputs 4) x = 200; 10 After the execution of (1) After the execution of (2) x After the execution of (3) x After the execution of (4) x x Previous value of x was overwritten 10 200
- 12. Sample Problem Write a program to take two numbers as input data and print their sum, their difference, their product and their quotient. Problem Inputs float x, y; /* problem Output float sum; /* float difference; x and y */ float product; /* y */ float quotient; /* divided by y */ two items */ sum of x and y */ /* difference of product of x and quotient of x
- 13. Sample Problem (cont.) Pseudo Code: Declare variables of x and y; Prompt user to input the value of x and y; Print the sum of x and y; Print the difference of x and y; Print the product of x and y; If y not equal to zero, print the quotient of x divided by y
- 14. Example Program #include <stdio.h> int main(void) { float x,y; float sum; function • name • list of argument along with their types • return value and its type • Body printf(“Enter the value of x:”); scanf(“%f”, &x); printf(“nEnter the value of y:”); scanf(“%f”, &y); sum = x + y; printf(“nthe sum of x and y is:%f”,sum); printf(“nthe sum of x and y is:%f”,x+y); printf(“nthe difference of x and y is:%f”,x-y); printf(“nthe product of x and y is:%f”,x*y); if (y != 0) printf(“nthe quotient of x divided by y is:%f”,x/y); else printf(“nquotient of x divided by y does not exist!n”); return(0); } inequality operator