C语言编程学习课件 (6).pdf

Programming In CProgramming In C Contents 01 02 constants variables constants and variables The essence of a program is to process the initial information(data)and then obtain the required information and results.Data have different expressions and storage methods in C programs,which involves concepts such as constants,variables,and data types.constants and variables constants A constant is an amount whose value cannot be changed in a program.The compilation system does not allocate storage space for constants,which are usually used to assign values to variables.There are several types of constants depending on the data type：integer constants:10,0,-25 real constants:5.15，-0.23 character constants:A,3,n,0 x8c string constants:”x”,”Welcome to C！”the character constants are usually enclosed in single quotes,such as A,n,0 x8c,etc.;the string constants are enclosed in double quotes,as shown here the x,Welcome to C!,and so on.constants and variables symbolic constant The symbolic constants replace a specific constant value with a symbol,an identifier,to show what the constant value actually means.It makes the program more readable and easier to maintain.Example:Given the radius of a circle,calculate the circumference and area of the circle.We can analyze this problem as follows:both the circumference and area of a circle involve PI(),the value of it is 3.14.Therefore,the symbol PI can be used instead of this constant value to enhance the readability of the program and facilitate the modification of the program when the calculation accuracy needs to be improved.constants and variables#include stdio.h#define PI 3.14 void main()double r,circum,area;r=1.0;circum=2*PI*r;area=PI*r*r;printf(circum=%f,area=%fn,circum,area);Result：Circum=6.280000,area=3.140000 Program codes：constants and variables variables A variable is an amount whose value can change during the execution of a program.The variables are essentially the memory space used to store data.The variables must be declared before use in the form of:：data-type-keyword variable-name;For example,：int a;float area;constants and variables variables The variables can be initialized at the same time as they are defined.int a=3;float area=0;char c=A;/We should note that if a variable is not initialized when it is defined,the value of the variable is generally a random number until an assignment statement or keyboard input statement modifies the value of the variable.constants and variables variables we can also define multiple variables of the same data type in one statement and initialize them at the same time.int x,y,z;int x=1,y=1,z=1;Error：int x=y=z=1 constants and variables variables many compilers require that all variables be defined before the first executable statement,otherwise it will cause compiling errors.#include stdio.h void main()int x;x=1;float y;y=2.8;printf(x=%d,y=%fn,x,y);How can we modify the program to pass the compilation normally?constants and variables variables In fact,we just need to adjust the statement that defines the variable y to the statement that assigns value to the variable x.In this way,the program will be compiled and linked normally and run correctly.Programming In CProgramming In C