03. Printing

Comments :

Comments are used to document our code, they help other programmers what our code is all about.

• Comments are not translated by compiler, they are deleted at time of compilation from output file.
• Source file will still contain comments, note that they are deleted from .exe or .out file

Single Line Comments :

Single line comments are started using double forward slashes and they are automatically terminated at end of line, means for termination you do not use any operator.

Syntax :

int main() {
    // This is a single line comment.
    return 0;
}

Multi-line Comments :

Multi-line comments are used to document code that spans multiple lines.

• Nesting is not allowed in multi-line comments, that a comment cannot contain another comment within it, this happens only in case of multi-line comment.
• They starts with a forward slash and an asterisk symbol.
• They end using asterisk symbol followed by a forward slash.

Syntax :

int main() {
    /* Hello
        This is a multiline comment.
    */

    // Most commonly used as :
    /*
    * First line
    * Second line
    */

    return 0;
}

Why do we need to plan a c program?

• We program in C because we want computer to do some task for us.

How do we program in C?

In order to program in c we have following instructions :

• Input Instructions (scanf)
• Output Instructions (printf)
• Conditional Instructions (while, if, for, loops)
• Declarative Instructions (variables, pointers)

Input Instructions :

• These instructions are required to take input from keyboard within our program.

Output instructions :

• These instructions are required to print output to standard output device, that is monitor.

Conditional Instructions :

• These instructions are used to write repetition code and code that evaluates on conditions.

Declarative Instructions :

• These instructions are used to reserve some memory in OS for our input.

Note : One tab equals 8 spaces.

Structure of C program :

        header files
        global variables

        main function declaration
            {
                body of program.
            }

Example of C program :

        #include<stdio.h> //header file

        int main() {    //main function declaration

            printf("Hello World");  //print output on screen
            return 0;       //returns value back from function.

        }

Addition in printf :

• More than one string passed passed to printf without commas will combine together to form a single string.

        int main() {
            printf("Hello" "Jayant" "Malik");
            return 0;
        }

Escape Sequences in printf :

• Escape sequences are used to shift cursor position at specific location.

        //escape sequences are used with backslash followed by specific letters.

        int main() {
            printf("Hello Jayant 1\n"); // prints a new line at end of text.
            printf("Hello Jayant 2\r"); // carriage return
            printf("Hello Jayant 3\b"); // backspace
            printf("Hello Jayant 4\t"); // tab
            return 0;
        }

Note : Use manual of ANSI C for more escape sequence characters.

Example of new line :

        int main() {
            int a=0;  // local variable
            while(a<=10) {  // while loop
                a++;    // a = a+1
                printf("This is line no : %d\n", a);
            }
        }

Example of carriage return

        int main() {
            int x = 0;
            // in borland compiler use delay(milli_second) function
            // to understand it better or use a higher value of x in loop.
            while(x<=100){
                x++;
                printf("%d\r",x);
            }

            return 0;
        }

Example of Backspace Escape Sequence Character :

        int main() {
            printf("Hello\b\b\b"); // shift cursor three position back.
            printf("AB");
            return 0;
        }

Let's See Borland Compiler Specific Code

        int main() {
            textcolor(10);  // sets text color
            textbackground(4)   // sets textbackground color\
            cprintf("Hello in Color");  // only works in borland
            delay(2000); //sets delay in milliseconds
            gotoxy(30,13); // changes cursor position (col, row)
        }

Let's Clear the Screen

• clrscr is a function used to clear the screen in DOS only.
• Think it as compiler specific code.

        int main() {
            printf("India is great.");
            clrscr();
        }