Objective: The purpose of this tutorial is learning the usage of -preprocessors -header files -printf(), scanf(), gets() functions -logic operators and conditional cases A preprocessor is a program that processes its input data to produce output to be used as an input for another program. The C preprocessor is the preprocessor for the C programming language. In many C implementations, C preprocessors are separate programs invoked by the C compiler as the first part of translation. The preprocessors handle directives for source file inclusion ( include), macro definitions ( define) and conditional inclusion ( if). Lines that begin with are called preprocessing directives. For example, if the lines #define XVal 100 #define YVal 200 occur in a file that is being compiled, the preprocessor changes the value of XVal to 100 and the value of YVal to 200. The identifiers XVal and YVal are called symbolic constants. An important property of define is; it can be written anywhere in the program but it should be noted that it only affects the lines written after it. The contents of the quoted strings are never changed by the preprocessors. The language of preprocessing directives is not strictly specific to the grammar of C, so the C preprocessor can also be used independently to process other types of files. #include "myheader1.h" is a preprocessing directive which exists at the head of the file and copies the contents of myheader1.h to the file when compilation occurs. An include file, which is also called as a header file, can contain define lines and other include files. The C system provides a number of standard header files. Some examples are stdio.h, string.h, math.h,.... These files contain the declarations of functions in the standard library, macros, structure templates, and other programming elements that are commonly used. The preprocessing directive #include "stdio.h" causes a copy of the standard header file stdio.h to be included in the code when compilation occurs. In ANSI C, whenever the function printf() or scanf() are used, the standard header file stdio.h should be included. This file contains the declarations, or more specifically, the function prototypes, of these functions.
Example 1: Usage of the Header File Header File (myheader1.h): #include "stdio.h" #include "math.h" #include "stdlib.h" #define A 5 #define Pi 3.14 C Source File (example1.c): #include "myheader.h" main() double c; c=pi*a; printf("new Pi value = %f",c); The printf() function is part of the standard C library and is used for output. The arguments of this function are control strings and other arguments, where control string is a string and may contain specifiers. The specifiers differ for different arguments. The prototype of printf function is below; printf("some words %d %f some words etc.",var1,var2,...); where var1 and var2 are arguments. The string may be consist of not only character literals but also format specifiers that control the output of other arguments. Commonly used conversion characters (Specifiers) are given below: The scanf() function is analogous to the function printf() but is used for input rather than output. Its first argument is control string and contains only specifiers. The other arguments are addresses. Its prototype is: scanf("%d %f possible specifiers",&variable1,&variable2,...);
scanf() reads from standard input and converts each argument as specified in the format string. The arguments after the format string must be addresses of variables such as (&var). The function gets() reads characters from standard stream for input (stdin) and stores the characters as a string. The storing process continues until a newline character ( \n )or the Endof-File is reached. The ending newline character ( \n ) is not included in the string. A null character ( \0 ) is automatically appended after the last character copied to str to signal the end of the C string. Notice that, gets() does not let you specify a limit on how many characters are to be read, so you must be careful with the size of the array pointed by str to avoid buffer overflows. Example 2: In this example you are invited to assign a character, a string, an integer and a floating number. Then, your assignments are printed on the screen. #include <stdio.h> void main() int a1, a2; float b1,b2; char c1,c2; char mystring[21]; a1=754; b1=457.5; c1='s'; printf("assign a character and assign a string:"); scanf("%c",&c2); // Character Assignment gets(mystring); // String Assignment printf("assign an Integer:"); scanf("%d",&a2); // Integer Assignment printf("assign a Floating number:"); scanf("%f",&b2); // Float Assignment /* The character \t is used for placing a space */ printf("\n a1=%d \t Your integer assignment=%d\n",a1,a2); printf("\n b1=%2.3f \t Your floating number assignment=%f\n",b1,b2); printf("\n c1=%c \t Your character assignment=%c\n",c1,c2); printf("\n Your string assignment: %s\n",mystring); printf("\n\n"); printf("congratulations!\t"); printf("example 2 is completed\n\n");
Relational, equality and logic operators are used to express the conditions in C programming. These operators return binary bits which indicate whether the comparison is true or not. If the comparison is true, it returns 1, otherwise it returns 0. The and and/or or operators are used to check the multiple conditions. And (&&) operator combines two conditions, and results true if both conditions are true. If one of the condition is false, then the result is false. Or ( ) operator combines two conditions, and results true if at least one of the conditions is true. If both conditions are false, then the result is false. Some of the relational and equality operators are listed below: If statement is used in conditional cases. When the execution of a statement depends on a desired condition, if() structure is used. The statement which is desired to be executed is written after if (condition). In the case, the condition written in the if() is satisfied, the desired statement is executed. Otherwise, program skips to the next statement.
Exercises: i) Write a program that prints out the below structure ************************************* **My Name is ******* **My Surname is ******* **My ID # is ******* ************************************* ii) Write a program that asks the user below questions and wants their replies ******** ID Documentation *********** 1) What is your Name? ******* 2) What is your Surname? ******* 3) What is your Address? ******* **************************************** iii) Guess the outputs of the following program without writing the codes in the case that the integers you assigned are, a) 50 and 50 (i.e. a=50 and b=50). b) 100 and123 (i.e. a=100 and b=123). c) 130 and 20(i.e. a=130 and b=20). #include <stdio.h> int main() int a,b,c; printf("assign two integers seperating them with a space:"); scanf("%d %d",&a, &b); c=a+b; if (c>150) printf("\n Summation is greater than 150\n"); printf("\n Summation is %d\n", c); if (c<=150) printf("\n Summation is less than or equal to 150\n");