1.3. C language¶

1.3.1. C++ shell¶

C language is chosen for different reasons. It is the king of all programming languages.

In order to try the examples, you can use the online shell: http://www.cpp.sh/. These shell is mainly a C++ compiler. Since C++ is compatible with C, we will use it in order to avoid you to install the compiler on your computer.

C++ online shell

The following code is the main function, the entry point of any C program. For now we are interested in the main function.

C program¶

#include <stdio.h>
int main()
{
  return 0;
}

1.3.1.1. Basic syntax¶

Any programming language borrow some concepts from mathematics: operations, variables, values and functions.

Operations are:

Addition
Subtraction
Multiplications
Division

Values can be:

Integers: 1, 2, 50, -10, ….
Real numbers: 0.2 , 1.5 , 2.5

Variables are like in mathematics, can hold numeric and non numeric values.

In C and other languages (not all), we must declare a variable before using it.

C program¶

#include <stdio.h>
int main()
{
    int a=10;
    int sum;

    sum = a+ 12;

    printf("the sum = %d",sum);

    return 0;
}

C language have different types of numeric variables:

int
double
float

1.3.1.2. Flow control¶

The execution of a program is usually sequential, It begin from the first instruction until the last one. Sometime we need to change the flow of execution. In C we have different contructs for flow control:

if else

switch case

for

while

Following a simple program than compare 2 variables.

If statement¶

#include <stdio.h>
int main()
{
    int a=10;
    int b=30;

    if (a == b)
    {
        printf("a is equal to b");
    }
    else if ( a > b )
    {
        printf("a is bigger than b");
    }
    else
    {
        printf("a is smaller than b");
    }

    return 0;
  }

An equivalent to if is the switch.

Switch statement¶

#include <stdio.h>
int main()
{
    int a=10;

    switch(a){
        case 0:
            printf("a is %d", 0);
            break;
        case 10:
            printf("a is %d", 10);
            break;
        default:
            printf("Value not present");

    }
    return 0;
}

1.3.1.3. Functions¶

Functions are useful to group instructions that can be used more than one time and to make the program more readable. In the follwing example, a function called max is created.

Fucntion¶

#include <stdio.h>

int max(int a, int b)
{
    if (a> b)
        return a;
    else
        return b;
}

int main()
{
    int num =10, num2=20;

    int m;

    m = max(num , num2);
    printf("the maximum is %d", m);

    return 0;
}