basics of C string and different sample problems with solutions.

1. Structured Programming Language
Strings in C
Mohammad Imam Hossain,
Lecturer, CSE, UIU

2. String
• A String is an array of characters terminated
by a special symbol named as null character
(represented as ‘0’ )
• Null character is also named as string-
termination character and used to identify
the length of the string.
• Logical illustration of a string consisting of n
characters:
X[0] X[1] X[2] … … … X[n-1] ‘0’

3. Defining a String
char string_name[expression];
• string_name  user chosen name for the
string
• expression integer expression indicates
the number of elements in the string,
including the null character
Sample Code:
char name[50];

4. String vs Char Array
Operations string char array
declaration char name[50]; ///max 49 characters char name[50]; ///max 50 characters
initialization char name[50]=“SPL";
or,
char name[50]={'S','P','L','0'};
or,
char name[50]={'S','P','L'};
char name[50]={'S','P','L'};

5. Reading a String
string char array
char str[50];
scanf("%s", str);
Or,
gets(str);
Or,
scanf("%[^n]", str);
char str[50];
int sz;
printf("Enter the size: ");
scanf("%d",&sz);
int i;
for(i=0;i<sz;i++){
scanf("%c",&str[i]);
}

6. Writing a String
string char array
char str[50];
printf("String : %sn",str);
Or,
puts(str);
char str[50];
for(i=0;i<sz;i++){
printf("%c",str[i]);
}
printf("n");

7. String I/O character wise
char str[50];
///reading string character wise
int i=0;
do{
scanf("%c",&str[i]);
i=i+1;
}while(str[i-1]!='n');
str[i-1]='0';
///writing string character wise
i=0;
while(str[i]!='0'){
printf("%c",str[i]);
i=i+1;
}
printf("n");

8. String Processing
• Way 1 using some predefined functions with help of
<string.h> header file
• Way 2 processing all characters individually

9. String Length
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
int i=0;
while(str[i]!='0'){
i++;
}
int length=i;
printf("Length %dn",length);
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
int length=strlen(str);
printf("Length %dn",length);
return 0;
}

10. String Concatenation
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char dest_string[50],src_string[30];
gets(dest_string);
gets(src_string);
printf("%sn",dest_string);
int len1=strlen(dest_string);
int i=0;
while(src_string[i]!='0'){
dest_string[len1+i]=src_string[i];
i++;
}
dest_string[len1+i]='0';
printf("%sn",dest_string);
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char dest_string[50],src_string[30];
gets(dest_string);
gets(src_string);
printf("%sn",dest_string);
strcat(dest_string,src_string);
printf("%sn",dest_string);
return 0;
}

11. String Copy
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char dest_string[50]="hello...",src_string[30];
gets(src_string);///world
int i=0;
while(src_string[i]!='0'){
dest_string[i]=src_string[i];
i++;
}
dest_string[i]='0';
printf("%s",dest_string);///world
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char dest_string[50]="hello…",src_string[30];
gets(src_string);///world
strcpy(dest_string,src_string);
printf("%s",dest_string);///world
return 0;
}

12. String Compare
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char str1[50],str2[50];
gets(str1);
gets(str2);
int i=0;
while(str1[i]!='0' && str2[i]!='0'){
i++;
}
int cmp=str1[i]-str2[i];
if(cmp<0){
printf("str2 is greatern");
}
else if(cmp>0){
printf("str1 is greatern");
}
else if(cmp==0) {
printf("Same stringn");
}
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str1[50],str2[50];
gets(str1);
gets(str2);
if(strcmp(str1,str2)<0){
printf("str2 is greatern");
}
else if(strcmp(str1,str2)>0){
printf("str1 is greatern");
}
else if(strcmp(str1,str2)==0) {
printf("Same stringn");
}
return 0;
}

13. LowerCase Conversion
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("%sn",str);
int i=0;
while(str[i]!='0'){
if(str[i]>='A' && str[i]<='Z'){
str[i]='a'+str[i]-'A';
}
i++;
}
printf("%sn",str);
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("%sn",str);
strlwr(str);
printf("%sn",str);
return 0;
}

14. UpperCase Conversion
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("%sn",str);
strupr(str);
printf("%sn",str);
return 0;
}

15. Reversing a String
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("%sn",str);
int len=strlen(str);
int first=0;
int last=len-1;
while(first<last){
int tmp=str[first];
str[first]=str[last];
str[last]=tmp;
first++;
last--;
}
printf("%sn",str);
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("%sn",str);
strrev(str);
printf("%sn",str);
return 0;
}

16. String to integer
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("string: %sn",str);
int digit=0;
int i=0;
while(str[i]!='0'){
digit=digit*10+str[i]-'0';
i++;
}
printf("integer: %dn",digit);
return 0;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
gets(str);
printf("string: %sn",str);
int digit=atoi(str);
printf("integer: %dn",digit);
return 0;
}

17. Integer to string
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
void int_to_str(int val,char str[], int base)
{
int index=0;
while(val!=0)
{
int rem=val%base;
if(rem>9)
{
rem='a'+rem-10;
str[index]=rem;
}
else str[index]='0'+rem;
val=val/base;
index++;
}
str[index]='0';
strrev(str);
return ;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
int num;
scanf("%d",&num);
printf("integer: %dn",num);
itoa(num,str,10);///value, string name, base of
conversion system
printf("decimal string: %sn",str);
itoa(num,str,2);///converting into binary
printf("binary string: %sn",str);
itoa(num,str,8);///converting into octal
printf("octal string: %sn",str);
itoa(num,str,16);///converting into hexadecimal
printf("hexadecimal string: %sn",str);
return 0;
}

18. Integer to string
Character wise processing Header file <string.h>
#include <stdio.h>
#include <string.h>
void int_to_str(int val,char str[], int base)
{
int index=0;
while(val!=0)
{
int rem=val%base;
if(rem>9)
{
rem='a'+rem-10;
str[index]=rem;
}
else str[index]='0'+rem;
val=val/base;
index++;
}
str[index]='0';
strrev(str);
return ;
}
#include <stdio.h>
#include <string.h>
int main()
{
char str[50];
int num;
scanf("%d",&num);
printf("integer: %dn",num);
itoa(num,str,10);///value, string name, base of
conversion system
printf("decimal string: %sn",str);
itoa(num,str,2);///converting into binary
printf("binary string: %sn",str);
itoa(num,str,8);///converting into octal
printf("octal string: %sn",str);
itoa(num,str,16);///converting into hexadecimal
printf("hexadecimal string: %sn",str);
return 0;
}
int main()
{
char str[50];
int num,base;
printf("Enter number and base to convert: ");
scanf("%d %d",&num,&base);
printf("integer: %dn",num);
int_to_str(num,str,base);
printf("string: %s",str);
return 0;
}

19. References
• Programming with C, Schaum’s outline, 3rd edition,
chapter 10
• https://www.tutorialspoint.com/cprogramming/c_str
ings.htm