What are the three basic program structures of C language?

The three basic program structures of C language are: 1. Sequential structures, such as expression statements, function call statements, and compound statements; 2. Selection structures, such as if statements; 3. Loop structures, such as for statements , while statement, do while statement.

1. Sequential structure

Expression statement, empty statement, function call statement, compound statement

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Program example:

Input an uppercase letter from the keyboard and request to use lowercase letters for output.

#include<stdio.h>
int main()
{
    char x,y;  
    
    scanf("%c",&x);
    
    if(x >= &#39;A&#39; && x <= &#39;Z&#39;)
    { 
        y=x+32;
    }
    
    else
    {
        printf("this is a erro"); 
    }
    printf("%c\n",y);
    return 0;
}

2. Selection structure

if statement program example:

Input three real numbers a, b, c, and output these three in order from small to large algebraic values number.

#include<stdio.h>
int main()
{
    float a,b,c,tmp;
   
    scanf("%f %f %f",&a,&b,&c);
    if(a > b)
    {
        tmp=b;
        b=a;
        a=tmp;
    }
    if(a > c)
    {
        tmp=c;
        c=a;
        a=tmp;
    }          
    if(b > c)
    {
        tmp=c;
        c=b;
        b=tmp;
    }        
       
    printf("%5.2f %5.2f %5.2f\n",a,b,c);
    return 0;
}

3. Loop structure

while statement, do while statement, for statement

for statement example:

Calculation: 1 2 3... .. 100.

#include<stdio.h>
int main()
{   
    int i,x=1;
    for(i = 2;i <= 100;i++)
    {
        x+=i;
    }
    printf("%d\n",x);
    return 0;
}

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