How to replace every specific character to another in a string C? - c

Question

I program in C. I'm supposed to create a program which identifies what is the most common character in a string and what's the second most common character.
I'm not sure why, but it's not working. the program should put into an integer the location of it. Not a pointer but if the most common is str1[i] then it will put into an integer the value of i. And so in the second most common. If it is str1[j] than it should put into an integer the value of j. then, it's supposed to replace the most commons with the second most common. The replacement function works, there's probably a problem in the loops although I can't figure out what is it.
Here's what I have (assume all of the integers and strings are declared in the beginning):
void stringReplace(char str1[], char ch1, char ch2);
int main()
{
char str1[100];
char ch1, ch2;
int i, j, p, n, len, counter1, counter2, first, second, times;
printf("Please enter the string - maximum = 100 characters:\n");
printf("User input: ");
gets(str1);
len = strlen(str1);
for(i = 0 ; i < len ; i++)
{
counter1 = 0;
for(j = 0 ; j < len ; j++)
{
if(str1[i] == str1[j])
{
counter1++;
}
if(counter1 > counter2)
{
first = i;
}
}
counter2 = counter1;
} //character which shows up most - found.
counter2 = 0;
for(p = 0 ; p < len ; p++)
{
for(n = 0 ; n < len ; n++)
{
if(str1[p] == str1[n])
{
counter1++;
}
if(counter1 < first && counter1 > counter2)
{
second = p;
}
}
counter2 = counter1;
}
ch1 = str1[first];
ch2 = str1[second];
stringReplace(str1, ch1, ch2);
puts(str1);
return 0;
}
void stringReplace(char str1[], char ch1, char ch2)
{
int i, j, len;
len = strlen(str1);
for(i = 0 ; i <= len ; i++)
{
if(str1[i] == ch1)
{
str1[i] = ch2;
}
}
}
Where's the problem ?

Answer 1

So you want to find the n max numbers in a string, being n=2, right?
I did a little working example for you. The code differs slightly from yours but it works well.
#include <stdio.h>
int main(int argc, char* argv[])
{
char str[] = "Algorithms Are Funnnn!\0";
int i=0;
int offset=33;
int ocurrs[94] = {0}; //considering from 33 to 126 (valid chars - ASCII Table [0-127]).
int max[2]={0};
while(str[i])
ocurrs[str[i++]-offset]++;
for(i=0; i<94; i++)
if(ocurrs[i]>ocurrs[max[1]]){
max[0] = max[1];
max[1] = i;
}
else if(ocurrs[i]>ocurrs[max[0]])
max[0]=i;
printf("chars '%c'(%d times) and '%c'(%d times) occurred most.\n",
offset+max[1], ocurrs[max[1]], offset+max[0], ocurrs[max[0]]);
return 0;
}
Also, try to stay away from gets as it's totally unsafe.
If you want to grab 100 chars max, use this instead:
char buffer[100];
fgets(buffer, 100, stdin);
Regards.

Answer 2

Can't resist to find an answer with some loops, without the populate occurence technique.
Very fun to code.
#include <string.h>
#include <stdio.h>
int main( void ) {
char szInput[] = "ONE DOES NOT SIMPLY WALK INTO MORDOR!";
int len = strlen( szInput );
int MaxCountSoFar_1 = 0;
int MaxIndexSoFar_1 = -1;
int MaxCountSoFar_2 = 0;
int MaxIndexSoFar_2 = -1;
int i, j, CountThatOne;
for ( i = 0; i < len; ++i ) {
if ( szInput[ i ] == ' ' ) continue;
// count that char
CountThatOne = 1;
// don't start from 0, they are already "counted"
for ( j = i + 1; j < len; ++j ) {
if ( szInput[ i ] == szInput[ j ] ) ++CountThatOne;
}
if ( CountThatOne > MaxCountSoFar_1 ) {
// push old first max to new second max
MaxCountSoFar_2 = MaxCountSoFar_1;
MaxIndexSoFar_2 = MaxIndexSoFar_1;
// new first max
MaxCountSoFar_1 = CountThatOne;
MaxIndexSoFar_1 = i;
} else {
// catch second one, but not if equal to first
if ( CountThatOne > MaxCountSoFar_2 && szInput[ i ] != szInput[ MaxIndexSoFar_1 ] ) {
MaxCountSoFar_2 = CountThatOne;
MaxIndexSoFar_2 = i;
}
}
}
if ( MaxIndexSoFar_1 >= 0 ) {
printf( "Most seen char is %c, first seen at index %d\n", szInput[ MaxIndexSoFar_1 ], MaxIndexSoFar_1 );
if ( MaxIndexSoFar_2 >= 0 ) {
printf( "Second Most seen char is %c, first seen at index %d\n", szInput[ MaxIndexSoFar_2 ], MaxIndexSoFar_2 );
}
}
return 0;
}