C

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... a programming language to follow B.

C is the core language of Unix and later GNU/Linux and the liberation of it's compiler software, gcc (the Gnu's alternative to the proprietary Unix C compiler (cc)), a foundation of the Free Software movement.

Key differences from Python

For those coming to C from Python, there are several important differences:

  • All variables have a fixed type (int, char, etc) and must be declared before use
  • Whitespace (spaces, tabs, newlines) does not generally matter in C. Blocks (like for loops, if statements) are always indicated with curly braces {}. Indentation is still recommended for readability however.
  • Source must be compiled first before executing.

Variables

Variables in C are strictly typed meaning they always are one particular kind of representation of information (an integer number, a character, a string of text).

  • int
  • char

int

int's or integers are for whole numbers (no fractional parts).

int i = 0;
printf("%d\n", i);

(short and long are "qualifiers" that then can be used before the word in as in:

short int foo;
long int bar;

In these cases the word int can be left out.)

Strings

Strings in C are arrays of characters.

char text[] = "pioneering jazz electronic organ recordings";
int textlen = strlen(text);
printf("%s id %d chars long, and starts with %c\n", text, textlen, text[0]);

Abstractly a string in C is simply a pointer; that is, a numeric memory location pointing to the first character of the text in the memory.

Loops

while

while (expression)
    statement

real example:

var i=0;
while (i<100) {
    printf("%d", i);
    i = i+1;
}

for

for (expr1; expr2; expr3)
    statement

for is actually just a compact form and is the same as saying:

expr1;
while (expr2) {
  statement
  expr3;
}

A simple counting example:

int i;
for (i=0; i<10; i++) {
    printf("Hello %d\n", i);
}

If-Else

if (expression)
    statement
else
    statement

Else-if allows for more than one possibility:

if (expression)
    statement
else if (expression)
    statement
else if (expression)
    statement
else
    statement