What are the three basic statements used to implement loop structures in C language

Three basic loop statements: 1. while loop statement, syntax "while(expression){statement block}"; 2. do-while loop statement, syntax "do{statement block}while(expression );"; 3. For loop statement, the syntax is "for (initialization statement; loop condition; self-increment or self-decrement) {statement block}".

The operating environment of this tutorial: windows7 system, c99 version, Dell G3 computer.

The three basic statements used to implement loop structures in the C language are: while loop statements, do-while loop statements, and for loop statements.

Tutorial recommendation: "c language tutorial video"

while loop statement

The general form of while loop is:

while(表达式){ 语句块 }

means, first calculate the value of "expression", when the value is true (non-0), execute the "statement block"; after executing the "statement block", calculate the value of the expression again, if True, continue to execute the "statement block"... This process will be repeated until the value of the expression is false (0), then exit the loop and execute the code after the while.

We usually call the "expression" a loop condition and the "statement block" a loop body. The entire loop process is the process of constantly judging the loop condition and executing the loop body code.

Use while loop to calculate the value of 1 added to 100:

#include  int main(){ int i=1, sum=0; while(i<=100){ sum+=i; i++; } printf("%d\n",sum); return 0; }

Run result:

5050

Code analysis:

1) When the program runs to while , because i=1 and i

2) Next, we will continue to judge whether i

3) Repeat step 2).

4) When the loop reaches the 100th time, the value of i changes to 101 and the value of sum changes to 5050; because i

The overall idea of the while loop is as follows: Set a loop condition with variables, that is, an expression with variables; add an additional statement to the loop body so that it can change the loop condition The value of the variable. In this way, as the loop continues to execute, the values of the variables in the loop condition will continue to change. There will eventually be a moment when the loop condition is no longer true and the entire loop ends.

What happens if the loop condition does not contain variables?

1) If the loop condition is true, the while loop will continue to execute and never end, becoming an "infinite loop".

2) If the loop condition is not true, the while loop will not be executed even once.

do-while loop

In addition to the while loop, there is also a do-while loop in C language.

The general form of the do-while loop is:

do{ 语句块 }while(表达式);

The difference between the do-while loop and the while loop is that it will first execute the "statement block" and then determine whether the expression is true. , if true, continue the loop; if false, terminate the loop. Therefore, the do-while loop must execute the "block" at least once.

Use do-while to calculate the value of 1 added to 100:

#include  int main(){ int i=1, sum=0; do{ sum+=i; i++; }while(i<=100); printf("%d\n", sum); return 0; }

Running result:

5050

Notewhile(iThe final semicolon;is a must.

for(表达式1; 表达式2; 表达式3){ 语句块 }

#include  int main(){ int i, sum=0; for(i=1; i<=100; i++){ sum+=i; } printf("%d\n",sum); return 0; }

5050