Lecture 02 Simple C Programs

Joseph Haugh

University of New Mexico

Attributions

Some slides and code are from Soraya Abad-Mota and Joan Lucas

Simple C Program 1

// Author: Joseph Haugh

/* Forward slash and asterisk to open/close comments */
// Double slash for a single line comment

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

Very simple C program.
A program is a “plain text” document.
File suffix is .c.
Always put your name in a comment at the top of your programs.

Simple C Program 1

// Author: Joseph Haugh

/* Forward slash and asterisk to open/close comments */
// Double slash for a single line comment

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

Every program has a main function.
Functions have open and closing braces.
Functions are a series of statements.
Body of the function is indented.

Simple C Program 1

// Author: Joseph Haugh

/* Forward slash and asterisk to open/close comments */
// Double slash for a single line comment

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

Two types of comments:
- Single-line: //
- Multi-line: /* ... */
printf function is from the stdio.h standard library.
# is the preprocessor directive symbol.

Simple C Program 1

// Author: Joseph Haugh

/* Forward slash and asterisk to open/close comments */
// Double slash for a single line comment

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

Compile and execute the program.
Produces two lines of output.
printf = “formatted print”.
string is enclosed in double quotes (“).
\n indicates that a newline should be printed.

Simple C Program 2

// Author: Joseph Haugh

#include <stdio.h>

int main() {
    printf("He");
    printf("llo, wo");
    printf("rld!\n");
    return 0;
}

Same output as before.
Number of printf statements doesn’t necessarily determine lines of output.
\n is the newline.

Simple C Program 3

// Author: Joseph Haugh

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How  \\are/  \"you\"  today?\n");
    return 0;
}

" (double-quote) has a special meaning as a string delimiter.
\ (back-slash) has a special meaning as the escape char.
back-slash “turns off” the special meaning of the character following it.

Simple C Program 4

// Author: Joseph Haugh

#include <stdio.h>

int main() {
    // C is "stream oriented", each statement can
    // spill over many lines

    printf
              (
        "Hello world!\n"
        
        )
                  ; // every stmt ends with ;
    return 0;
}

C is “stream oriented”.
Stream oriented verse line oriented
The printf statement can span several lines in the source code file.
This is legal, but poor “style”, since this is much harder to read.
Every statement ends with a semi-colon.

Simple C Program 5

// Author: Joseph Haugh

#include <stdio.h>

int main() {
    // C is "stream oriented", each statement can
    // spill over many lines

    printf
              ( // strings cannot be split over a line
        "Hello,
         world!\n"
        
        )
                  ; // every stmt ends with ;
    return 0;
}

Strings cannot be split over a line.
Compiling this code produces errors.

Simple C Program 5

// Author: Joseph Haugh

#include <stdio.h>

int main() {
    // C is "stream oriented", each statement can
    // spill over many lines

    printf
              ( 
        "Hello, "  // adjacent strings are
        "world!\n" // combined into one string
                   // we do NOT use "+"
        )
                  ; // every stmt ends with ;
    return 0;
}

Two adjacent strings are combined into one String by C.
No need to use the + operator, as in:
- "Hello" + "world"
The first homework will be assigned later today.