This document discusses strings in C programming language. It defines a string as an array of characters terminated by a null character. It explains how to declare and initialize strings, read and write strings, determine string length, concatenate strings, copy strings, compare strings, convert between strings and integers, and various string processing functions like reversing, converting case, etc. It provides examples of implementing these string operations both through character-wise processing and using predefined string header functions.

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