STL_STUDY

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Part 1. C Language

• In this section we are going to study how to use scanf and printf

scanf / printf

• C language function for standard input and output
• Defined in <stdio.h> header file
• can be used in C++

Formatting

• %d : decimal

int n;  
scanf("%d",&n); // input : 5  
printf("%d\n",n); // output : 5  

• %i : decimal

int n, m;  
scanf("%d %i",&n, &m); // input : 10 10   
printf("%d %d\n",n, m); // output : 10 10  
scanf("%d %i",&n, &m); // input : 10 010   
printf("%d %d\n",n, m); // output : 10 8  
scanf("%d %i",&n, &m); // input : 10 0x10   
printf("%d %d\n",n, m); // output : 10 16  

• %x : hexadecimal
• %o : octal
• %s : string

char s[100];  
scanf("%s", s); // input : hello world!   
printf("%s\n", s); // output : hello  

• %c : character

char c;  
scanf("%c", &c); // input : hello world!   
printf("%s\n", c); // output : h  

• %f : float
• %lf : double
• %Lf : long double

Return value of scanf

• On success, the function returns the number of items of the argument list successfully filled.

while ( scanf("%d %d",&a, &b) == 2 ) // read file to the end

Ignore white space and line break

• scanf ignores white space and line break

for ( int i = 0; i<5; i++) {
    scanf("%d", &n); // input : 10 20 30 40 50
    printf("%d\n",n); // output : 10 20 30 40 50 
}
for ( int i = 0; i<5; i++) {
    scanf("%d", &n);// input : 10 
                    //          20      30 
                    //          40 
                    //              50
    printf("%d\n",n); // output : 10 20 30 40 50 
}

Case Study.

• Reading char right after reading int

int n;
char a,b,c;
scanf("%d", &n); // input : 10
scanf("%c %c %c", &a, &b, &c); // input : A B C
printf("%d\n", n); // output : 10
printf("%c %c %c\n", a, b, c);  // output :  
                                //          A B

Problem

• character variable A read '\n' instead of 'A'

Solution 1. Ignore '\n' with white space before reading character

int n;
char a,b,c;
scanf("%d", &n); // input : 10
scanf(" %c %c %c", &a, &b, &c); // input : A B C
printf("%d\n", n); // output : 10
printf("%c %c %c\n", a, b, c);  // output : A B C

Solution 2. Explicitly read '\n' after reading int

int n;
char a,b,c;
scanf("%d\n", &n); // input : 10
scanf("%c %c %c", &a, &b, &c); // input : A B C
printf("%d\n", n); // output : 10
printf("%c %c %c\n", a, b, c);  // output : A B C