Preliminary understanding of C language

#include <stdio.h>//contains header file, standard input output header file standard input outputs;

#include <math.h>

void Main () {

printf ("This is a C program\n");

}

The main function is the entrance to the C language program.

{} Indicates the starting point of the main function.

printf ("This is a C program\n");//The text within the double quotation marks is printed to the screen.

\ nplease print a carriage return.

Type (data type):

char,unsigned char,signed Char: up to 1 bytes;

short,unsigned Short int: 2 bytes;

int,unsigned int unsigned integer (positive integer): 4 bytes (32-bit machine);

long,unsigned Long Integer: 4 or 8 bytes (length greater than or equal to int);

Float single-precision floating-point number: 4 bytes;

Double double-precision floating-point number: up to 8 bytes;

What the data type means: It means more efficient memory space savings.

SCANF is to obtain data from the keyboard;

printf fetches data from memory;

The rules for variable naming in C language: Each variable must begin with a letter and an underscore, consisting of letters, underscores, and numbers.

The case is two different characters.

Cannot use the keyword of c to do variable name.

The concept of constants:

A constant is a quantity that cannot be changed. Because the literal value of a constant represents its numeric size, it is also called a literal constant. Constants can represent values of various data types. Its data type can also be learned directly from its literal form.

Constants constants:

Const: Add the const keyword before a variable to become a constant.

The value of a constant that cannot be changed once initialized.

Constants must be initialized at the same time as they are created.

The concept of a variable:

A variable is a quantity that can be changed. Variables are made up of two parts: variable names and variable values. Variable teacher an identifier; the value of a variable is a data value.

When defining a variable in the C language: int const and const int are the same or indifferent;

The function of "%-8d" in C language is:

Defines the output format so that the output int data occupies at least 8 positions and is positioned from the leftmost end of the 8 position.

If the displayed data is less than 8 characters, add a space to complement the 8 locations;

If the data displayed is more than 8 characters, the subsequent position continues to occupy.

The function of "\ T" in the C language is the equivalent of a TAB key, which is intended to align the output results.

Here are two simple examples in C language:

Implement subtraction:

#include "stdafx.h"

int main (int argc, char* argv[])

{

int a=0;

int b=0;

printf ("Please input a,b\n");

scanf ("%d", &a);

scanf ("%d", &b);

printf ("%d+%d=", a,b);

printf ("%d\n", a+b);

printf ("%d-%d=", a,b);

printf ("%d\n", a-b);

printf ("%d*%d=", a,b);

printf ("%d\n", a*b);

printf ("%d/%d=", a,b);

if (b!=0) {

printf ("%d\n", A/b);

}else{

printf ("Please re-enter");

}

return 0;

}

The 99 multiplication table in C language:

#include "stdafx.h"

int mian (int argc,char*argv[]) {

int a[9];

int b[9];

int i;

Int J;

for (i=1;i<=9;i++) {

A[i]=i;

printf ("\ n");

for (j=1;j<=i;j++) {

B[j]=j;

printf ("%d*%d=%-3d", B[j],a[i],b[j]*a[i]);

}

}

return 0;

}