problem in c code while(*s)

[engineer khan]

Hello everybody ! please explain the following code to me
whats while(*s) how it works

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Code C - [expand]
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void send_to_modem(char *s){
 while(*s)
 uart1_write(*s++);
 uart1_write(0x0d);
}

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[OYTIS]

The code writes a zero-terminated string to UART1, adding carrier return in the end. "while(*s)" is a short form of "while((*s) != '\0')", which means loop while char, "s" points to is not equal to zero. Note that "s" is incremented on each iteration, so that s points to the next character in the string.

 

[milan.rajik]

Read about strings and pointers in C programming books.

 

[tantalos]

s is a pointer to a location in memory that holds a variable of type char. *s retrieves the variable value that s points to.
As the pointer moves to the next location in memory in the expression *s++ the loop while(*s) { ... } will be executed as long as the value that s points to is not 0.