C language tutorial (3) - if and loop

Table of Contents

expression

Math Expression

Relational Expression

Logical Expression

if

if

if else

loop

while

for

Ask a question:

---

expression

Math expression

The value of a mathematical expression is a number.such as

1+2;2*3;4-4;5/2;3%2;

For mathematical expressions, 0 is false and non-0 is true.

Relational Expression

Relational expressions can only be one of two values, true and false.such as

1<2;//true 1<21>2; // false 1>21==2;//false 1=21!=2;//true 1≠21<=2;//true 1≤21>=2;//false 1≥2

Logical expression

&& or || or ! in logical expressions

If expression A&&expression B, if expression A is true, execute expression B; if expression A is false, the following does not need to be executed.This situation is called a short circuit.The entire expression is only true if both expression A and expression B are true.

If expression A||expression B, if expression A is true, expression B does not need to be executed, and the following does not need to be executed.This condition is called a short circuit.As long as one expression is true, the whole expression is true.

!: Negative operation.Turning true into false and false into true.

if

if

if can control the selection process, the usage is as follows:

if(expression){code}

If the expression is true, execute the code inside the {} (compound statement).

if else

The usage of if else is as follows:

if(expression){code 1}else{code 2}

If the expression is true, execute code 1, otherwise execute code 2.

loop

How to calculate the sum of the numbers from 0 to 10 in C language?

while

The usage of while is as follows:

while(expression){code}

If the expression is true, loop through the code.Each time through the loop, check whether the expression is true or not.

How to use while to write the above question?The code is as follows:

#includeint main(void){int i=0, num=0;while(i<=10){num += i; //num += i is num = num + ii++; // i++ is i+=1}printf("0+1+2+...+10 is %d\n", num);return 0;}

Results:

0+1+2+...+10 is 55

for

The usage of for is as follows:

for(expression 1 (can not write); expression 2 (can not write); expression 3 (can not write)){code}

Expression 1 is executed once before the loop; if expression 2 is true, the loop executes the code.Once in each loop, check whether expression 2 is true.Expression 3 represents the code to be executed after each loop.

How to use for to write the above question?The code is as follows:

#includeint main(void){int i, num=0;for(i=0;i<=10;i++){num += i; //num += i is num = num + i}printf("0+1+2+...+10 is %d\n", num);return 0;}

Results:

0+1+2+...+10 is 55

A problem:

Is the following loop an infinite loop?

short i;for(i=0; i>-1; i++){}

Please post your answers in the comments section.