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What is a variable? Variables are natural and constant are absolute. The constants are 1, 2, 3, 4.5, 10.6. And so on a fixed number, and the variable is based on what we learned in primary school, x is a concept, we can make it 1, or we can make it 2, how much we want it to be is up to our program.

So in the mathematics we learn in primary school, there are several categories, negative numbers, positive numbers, integers and decimals. In the C language, in addition to the differences between the names and what we learn in math, there are no restrictions on the size of the data. What is a little complicated in this center is that the scale of the data in C51 can be the same as that of other programming situations, so the diagram below only represents C51, and other programming situations can be different. Everyone knows that there is such a thing.

The basic data types of C language can be divided into character type, integer type, long integer type and floating point type, as shown in figure 4-1.

Figure 4-1 C speech basic data type

In figure 4-1, there are four basic types, each of which includes two types. Character type, integer type, long integer type, in addition to the differences in the size and size of the values that can be expressed, most of them can only express integers, while those of unsigned type can only express positive integers, and if you want to express negative integers, you must use signed type, if you want to express decimals, you must use floating point type.

For example, in the program that flashed LED lights at the beginning of the last lesson, we used unsigned int iTunes 0; the value scale of this central I is 0mm 65535. In the following for statement, if we change the original person 30000 to 70000, for.

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