Different types of data occupy different storage unit lengths in memory. Take the compilation environment of VC++6.0 as an example, basic integer (int) data is allocated 4 bytes and short integer (short int) data is allocated 2 bytes. Let's take short int as an example. 1 byte is 8 binary bits, and each short integer data is allocated 2 bytes, namely 16 bits. For signed short integers (default), the leftmost bit is the sign bit, 0 means positive, and 1 means negative. The maximum quantity that can be stored is 0111111165438. The minimum number is1000000000000, which is converted into decimal -32768. Beyond this range, it is "overflow". For example:
short int a，b，c，d； a = 32767b = a+ 1； c =-32768； d = b- 1；
printf("b=%d\t "，b)； printf("d=%d\n "，d)； The output result is b=-32768 d=32767.
For unsigned short integers, the minimum value is 00000000000000, and the maximum value is111111. For example:
Unsigned short integer e=65535, f; f = e+ 1；
printf("f=%d\n "，f)； The output result is f=0.
Second, the operator
Arithmetic operators are+,-,*,/,%,++,-. Among them, the * sign in the expression cannot be omitted, such as b2-4ac. The expression is written as b * b-4 * a * c ./ and% should be distinguished,/is the quotient, and% is the remainder. If a is divisible by b, it means that a%b==0. There are two ways to use++.One is i++ and I-. First, use the original value of I, and then add or subtract1with the value of I; The second ++i, -I first adds or subtracts 1 from the value of i, and then uses the new value of i. For example:
int I = 1 1； printf("%d\n "，i++ * 1/3)； The output result is 3.
int I = 1 1； printf("%d\n "，++ I * 1/3)； The output result is 4.
Self-addition and self-subtraction operators will be often used in later learning, so you should understand them well.
The logical operator is&; & amp,||,! . In a logical expression, not all logical operators are executed, but only when the next logical operator must be executed can the solution of the expression be found. A & amp& ampb only judges the value of B when A is true. In other words, if A is false, B will not execute it. Similarly, if a || b and A are true, then B does not need to execute. For example:
int m= 1，n= 1，a= 1，b = 1；
Printf ("expression =% d \ t ",(m = a>b) and amp & amp& amp(n = a & gtb))；); printf("m=%d，n=%d\n "，m，n)；
The output result is the expression =0 m=0, n= 1.
The priority order of common operators is:! , arithmetic operator (++,-higher than *,/,% higher than+,-), relational operator (>; ,>=,<,<= higher than = =,! =), & amp& amp|||, assignment operator, comma operator.
Third, compare the size of the numbers.
For example, write a program to output the maximum value of three integers. Most students who are new to C language can complete this program in computer practice, but their thinking is not very good. Adjust the algorithm ideas to facilitate future programming.
Master ()
{ int a，b，c，maxmax = a；
If (b & gtmax)max = b；; if(c & gt； max)max = c； printf("max=%d\n "，max)； }
Similarly, write a program to output the maximum value of 10 integer.
Master ()
{ int a[ 10]，max，I； for(I = 0； I < = 9; i++) scanf("%d "，& ampa[I])；
max = a[0]； for(I = 1； I < = 9; i++)if(a[I]& gt； max)max = a[I]；
printf("max=%d "，max)； }
Fourth, the switch statement
The processing selection structure includes if statement and switch statement. Switch statement is used to deal with multi-branch selection structure, and there are many points for attention when using it. Two points are emphasized here.
Constants after 1.case cannot be written as expressions.
For example, write a program to judge the grade of students' grades. 90 ~ 100 is a, 80 ~ 90 is b, 70 ~ 80 is c, 60 ~ 70 is d, and below 60 is e.