Getting Started

The only way to learn a new programming language is by writing programs in it. The first program to write is to print most common words we use, when we meet, i.e.:

Sat Sri Akaal 

which is a form of greeting, like “Hello”, or “Good morning”. For this you need to type the program text somewhere, compile it successfully, load it, run it, and find out where your output went. With these mechanical details mastered, everything else is comparatively easy.

In C, the program to print Sat Sri Akaal is:

#include <stdio.h> 

int main(void) 
{ 
    puts("Sat Sri Akaal"); 
    return 0;
} 

Just how to run this program depends on the system you are using. If you are following our instructions at Github, then create the program in a file named main.c in folder source, then compile it with following commands from build directory (folder):

cmake ..
make

If you haven’t fumbled, not commited any mistake, such as omitting a character or misspelling something, then compilation will proceed and you will read a message like:

[100%] Built target main

which mean you are able to built the target with name main, which is the outcome of compilation process. If you run main by typing the command:

./main

it will print

Sat Sri Akaal

On other systems, the rules will be different; check with a local guru / expert / hacker.

Let is try to understand the C program. A computer program written in C language, whatever its size, consists of functions and variables. A function contains statements that specify the computing operations to be done, and variables store values used during the computation. Our example is a function named, main. Normally you are at liberty to give functions whatever names you like, but main is special. Your program begins executing at the beginning of main. This means that every program must have a main somewhere.

main will usually call other functions to help perform its job, some that you wrote, and others from libraries that are provided to you. The first line of the program,

#include <stdio.h> 

tells the compiler to include information about the standard input/output library; this line appears at the beginning of many C source files.

One method of communicating data between functions is for the calling function to provide a list of values, called arguments, to the function it calls. The parentheses (round brackets) after the function name surround the argument list. In this example, main is defined to be a function that expects no arguments, thus void written there (if you wish, you may ommit it).

The statements of a function are enclosed in braces {}. The function main contains only one statement,

puts("Sat Sri Akaal"); 

The first C program

#include <stdio.h>          // include information about standard library 
int main(void)              // define a function named main that receives no argument values
{                           // statements of main are enclosed in braces 
    puts("Sat Sri Akaal");  // main calls library function puts
                            // to print this sequence of characters
    return 0;               // indicate successful execution
}

A function is called by naming it, followed by a parenthesised list of arguments, so this calls the function puts with the argument "Sat Sri Akaal". puts is a library function that prints output, in this case the string of characters between the double quotes.

A sequence of characters in double quotes, like "Sat Sri Akaal", is called a “character string” or “string constant”.

puts("Sat\nSri\nAkaal");

If we change our program as above, then all three world, namely Sat. Sri, and Akaal will in three separate lines.

The sequence \n in the string is C notation for the newline character, which when printed advances the output to the left margin on the next line.

If you try something like

puts("Sat Sri Akaal 

the C compiler will produce an error message.

In place of puts, you may also try another library functon printf. In source file of our first program, replace puts with printf, and observe the similarities and differences.

printf never supplies a newline (\n) automatically, so several calls may be used to build up an output line in stages. Our “first program” could just as well have been written

#include <stdio.h> 
int main(void) 
{ 
    printf("Sat "); 
    printf("Sri "); 
    printf("Akaal"); 
    printf("\n");
    return 0; 
}

to produce identical output.

Notice that \n represents only a single character. An escape sequence like \n provides a general and extensible mechanism for representing hard-to-type or invisible characters. Among the others that C provides are \t for tab, \b for backspace, \" for the double quote, and \\ for the backslash itself, and a few more.

Exercise

1. Run the program to print “Sat Sri Akaal” on your system or on code.gndec.ac.in Experiment with leaving out parts of the program, to see what error messages you get.

2. Experiment to find out what happens when printf’s argument string contains \c, where c is some character not listed above.