The C/C++ programming language consists mostly of expressions and statements. In fact, many statements are also expressions and vice versa.

Statements

#include <stdio.h>
int main(int argc, char ** argv) {
    printf("Hello, World!\n");
    return 0;
}

This program will output the constant string "Hello, World!", and every line that is ended with ; is called statement.

printf("Hello, World!\n");
return 0;

Expressions

But actually,

printf("Hello, World!\n");

is also expression, because printf function is returning a value which is the number of the printed characters. So let's assign it to a simple integer variable here.

#include <stdio.h>
int main(int argc, char** argv) {
    int x = printf("Hello, World!\n");
    printf("printf retruned %d\n", x);
    return 0:
}

x = printf returns an integer value. So I can print that with another printf statement, So the output of this program will be

$ gcc hello.c
$ ./a.out
Hello, World!
printf returned 14

So that means the first printf has printed 14 characters. So the expression is a unit of computation and every expression has a value. the statement in another hand is a unit of execution and the statement is terminated by a ;

Compound statement

when multiple statements are grouped together with curly braces. These are called compound statements. They're also sometimes called blocks.

int main(int argc, char** argv) {
    int x = printf("Hello, World!\n");
    printf("printf retruned %d\n", x);
    return 0:
}

every curly braces defining a scope, we will know more about it in the coming topics.